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An Introduction to Human Factors in Medical Devices

1. The remainder of this section describes methods used by human factors professionals in designing user interfaces for equipment DOCUMENT REVIEWS Studying documents about human factors and related device issues is valuable early in the development of a product Such information is easy to obtain and is useful in understanding user interface issues and human factors methods The Literature Human factors articles technical reports and textbooks offer substantial information Numerous journals magazines and newsletters report studies and surveys on the combined effects of design environment and work conditions upon 18 Do It By Design device operation Also of value are design case studies and product evaluations Research design and conceptual articles of value also can be found in such human factors publications as Human Factors Ergonomics Ergonomics in Design The Journal Of Applied Ergonomics and the Proceedings of the Human Factors and Ergonomics Society HFES Annual Meetings The proceedings of sessions conducted by the Human Factors and Ergonomics Society HFES Medical Systems and Rehabilitation Technical Group are especially relevant as are those of the Human Engineering Division 21 of the American Psychological Association Textbooks offer a broader view of human factors principles design process environmental factors and humans as device operators Finally technical reports standards and guidelines from governm
2. Callan J R Kozlowski T A Meringola E D amp Meadows S K 1990 Human factors in self monitoring of blood glucose Final report NTIS PB 90 260886 AS San Diego CA Pacific Science amp Engineering Group for the FDA 45 Do It By Design Kortstra J R A 1995 Designing for the user Medical Device Technology Jan Feb pp 22 28 Le Cocq D 1987 Application of human factors engineering in medical product design Journal of Clinical Engineering 12 4 271 277 Loeb G L Jones B R Leonard R A amp Kendra B 1992 Recognition accuracy of current operating room alarms Anesthesia amp Analgesia 75 499 505 Meister D 1985 Behavioral analysis and measurement methods N Y Wiley Meister D 1976 Behavioral foundations of system development N Y Wiley Nielson J 1993 Usability engineering Chestnut Hill MA Academic AP Professional Pickett R M and Triggs T J 1975 Human Factors in Heath Care Papers presented at an international symposim held in Lisbon Portugal June 1974 D C Heath and Company ISBN 0 669 95885 9 Reason J 1990 Human error Cambridge England Cambridge University Press Rouse W B 1980 Systems engineering models of human machine interaction New York North Holland Salvendy G Ed 1987 Handbook of human factors New York John Wiley amp Sons Sanders M S amp McCormick E J 1993 Human factors in engineering design New York
3. and consoles associated with medical devices should fit the user population Data on body dimensions of various populations including arm length body height leg length and numerous other bodily specifications are collected and published in a variety of documents Such data in conjunction with dynamic fitting trials are important in designing equipment so that controls are within reach and seating arrangements are comfortable There are important implications for anesthesia workstations prosthetics and rehabilitative devices these data apply to many home use devices such as wheelchairs in which portability compatibility with structures and compactness are important Knowledge of the clinical or home use environments is extremely important 14 Do It By Design Important but more elusive are the Figure 4 Medical Tools biomechanical characteristics of tools such as hammers dental tools surgical instruments control knobs keyboards and other devices that require substantial dexterity or strength and or involve repetitive motions For example instruments such as those shown in Figure 4 can be difficult to use if they are not tested with users Physicians and dentists often must precisely manipulate instruments in limited spaces There may be problems associated not only with demands on dexterity and Design for fine strength but those related to visibility reach and manipulations is Mery compatibility with other equipme
4. efficient use There have been cases in which patients were seriously injured when a nurse over infused a patient after reading the number 7 as a 1 Because the flow rate readout was recessed in the infusion pump display panel the top of the 7 was blocked from view by the display surface even at modest vertical viewing angles There have been similar reports of flow rates which had been misread when viewed from the side for example 355 ml read as 55 ml These few examples illustrate the fact that seemingly small design flaws can result in serious problems Tailoring a few general human factors guidelines such as those below to particular devices will decrease the risk of such problems Following are some rules of thumb for designing the user interface Rules of Thumb Make all facets of design as consistent with user expectations as possible Both the user s prior experience with medical devices and well established conventions are important considerations Design workstations controls and displays around the basic capabilities of the user such as strength dexterity memory reach vision and hearing Design well organized and uncluttered control and display arrangements Ensure that the association between controls and displays is obvious This facilitates proper identification and reduces the user s memory load Ensure that the intensity and pitch of auditory signals allow them to be heard easily by device users Con
5. individuals from a specified population The sessions are conducted to obtain opinions 22 Do It By Design and ideas regarding a product concept A focus group typically consists of about six to eight healthcare practitioners or lay users These individuals should be prospective users of the new device under consideration Such sessions are best conducted by experienced moderators working from scripts prepared in concert with the design team Well conducted sessions yield numerous ideas about user interface design alternatives and user requirements Remember that users generally have limited knowledge of design alternatives and principles Thus the best approach is to weigh subjective data against known interface characteristics human factors expertise and user performance data Finally because dominant individuals can bias findings it may be wise to also consider one on one sessions Physical Measurements Measuring sound and light will help in the assessment of such design moderated factors as glare contrast and masking by ambient noise Also measurements of both physical reach and visual envelopes are necessary in workstation design Samples from different facilities will produce data to profile typical work environments Summary Observational studies and interviews can pay handsome dividends The design team gains a better appreciation of the user population the working environment potential hazards problems with predicate devi
6. quickly and properly identify controls switches and displays reach and accurately set controls read displays accurately and associate controls with their related displays Desirable features include functional grouping of controls and displays unambiguous labels and easy to operate keys Clear instructions and effective warnings also are important Examples of Errors Related to Hardware Design The following three examples of problems were abstracted from the Medical Device Reporting MDR system and FDA device recalls Aphysician treating a patient with oxygen set the flow control knob as Figure 1 Controls show in Figure 1 between 1 and 2 liters per minute not realizing that the With no flow scale numbers represented discrete between settings rather than continuous settings the user was There was no oxygen flow between tricked into the settings yet the knob rotated dangerous smoothly suggesting that errors intermediate settings were possible The patient an infant became hypoxic before the error was discovered One solution would have been a rotary control that snaps into a discrete setting Some indication of flow also should have been provided There have been numerous reports and recalls associated with defibrillator design These include paddles that are hard to remove from Do It By Design their retaining wells and confusing arrays of poorly labeled controls and displays that inhibit safe
7. 3 Could the consequences of error be serious for the patient or user 4 n doing actual testing s someone integral to the design team focusing on the user related issues Are users involved Are hardware and software designers technical writers and others coordinating their efforts with respect to human factors Hasatest plan been developed e Have user requirements been developed and are they being updated 5 Has the design team checked the literature and company files for useful human factors information 6 What studies analyses and test steps are being performed Are staff examining all relevant issues related to the installation of accessories and operation of the device 7 Has the project team done testing in simulated and or actual environments 8 Have user requirements been met 9 User interface changes can be inadvertantly introduced into production models during manufacturing Have they been accounted for 39 Do It By Design GLOSSARY The definitions in this section are pertinent to this document In some cases they are general and may not coincide with a specific usage or application Administration set intravenous A device used to administer fluids from a container to a patient s vascular system through a needle or catheter inserted into a vein The device may include the needle or catheter tubing flow regulator drip chamber filter stopcock fluid delivery tubing connectors capped si
8. Cognition refers to higher level mental phenomena such as memory information processing use of rules and strategies hypothesis formation and problem solving For example the multiple hierarchical pathways and seemingly unlimited information often found in computerized devices can rapidly exceed the user s memory limits Do It By Design Therefore a designer should develop easy to use retrieval systems taking advantage of well established semantic and symbolic techniques for screen and menu design Expectancies People are predisposed to react to new situations according to established habits Designers can take advantage of existing conventions population stereotypes such as the color red equals danger in the general population as well as the standards and conventions of the medical community Designs consistent with ingrained habits will facilitate performance and reduce training time Designs that conflict with such habits can lead to errors Mental Models Based on experience people form abstract concepts about how complex phenomena actually work For example anesthesiologists form mental representations of patient status based on information about respiration heart rate oxygen levels and other bodily processes Monitors should present such information in a manner consistent with such models There is a need for thorough assessment of how users conceptualize device operation in patient treatment and monitoring This is a com
9. EU ex bee Sd ead Seed x 33 Initiating a Company Human Factors Program eee aee 33 Personnel cncecu cece eave a ak ae ON PRM eRe Ramee eae eee 33 PROSCUNCES ew eret 33 Characterizing the Human Factors Efforts 2 0005 34 EE 35 Recognizing Problems 2 lt 0 c c20 h bed ba ceded dbatececdsaciae nes 35 Evaluating Already Purchased Devices 00 eee eee 36 Evaluating Devices Before Purchase 2200000 ee ees 37 Analyze and Test the Model 0 37 Final COmMent oris a cian isn eve NOCERE SIDE cake QC nc eee ewe 38 Polnis 10 CONSIGEr 52434 5511 ene Pol CR EE ded dco dc ario po Ea 39 GLOSSARY zac ERR ENSE eEEGE Ea xa WERE HEGAVeEVE Ni E ER Ree 40 REFERENCES FOR FURTHER READING 00 0000 43 vii Do It By Design The mention of commercial products their sources or their use in connection with material reported herein is not to be construed as either an actual or implied endorsement of such products by the Department of Health and Human Services Although this guidance document does not create or confer any rights for or on any person and does not operate to bind FDA or the public it does represent the agency s current thinking on guidance for medical devices Where this document reiterates a requirement imposed by statute or regulation the force and effect as law of the requirement is not changed in any way by virtue of its inclus
10. are possible Then they can analytically pinpoint potential causes and draw conclusions about consequences and appropriate design solutions This information may be tabulated to provide a concise overview for further analysis and or input into the design concept and requirements The utility of such an approach is illustrated by electrocutions of infants Figure 8 Electrical Leads amp resulting from the insertion of patient Hazard Analysis electrode leads into AC power cords LED by parents siblings and healthcare 5 professionals see Figure 8 If Aw extension analysts had considered the use environment user populations and x potential errors the hazard probably Electrode would have been identified and the TS appropriate solution such as recessed body leads implemented One should note that hazard analyses may pinpoint low frequency errors not discovered in prototype tests involving users Some hospitals have many unprotected body leads in inventory Hazard analyses can identify the hazards and their solutions Patient Cable Other Analyses Other techniques include time lines and workload analysis Time lines represent sequential and simultaneous responses required of the user which are graphed over time Workload analysis can produce measures ranging from estimated expenditures of energy for physical tasks to subjective and performance measures of the performance requirements imposed on operators Both of these m
11. broader such as novice users should reach high levels of efficiency after a few hours of training Efficiency in terms of errors and time can be hard to determine while the design concept is in flux At some point in development a clearer picture of expected performance levels will emerge and detailed performance criteria need to be defined If possible these should be quantitative and should be linked to safe use and any other goals important to the manufacturer and user population In addition to specific strengths and weakness in device operation a number of other design related measures may be important such as Calibration time accuracy changes in error probability and other measures Various measures are used in testing Errors may be recorded by direct observation videotaping or electronic data logging Speed of operation is based on completion times of tasks and other objective measures may be used such as the number of times the user must refer to the device manual Verbal responses also are important and can be obtained by interviews or by having users state the rationale for their actions as they progress through task sequences Also subjective impressions of usability and potential safety problems are important Facilities Depending on resources and the nature of the test a modest usability laboratory may suffice A limited facility might consist of a room containing a table chairs electrical outlets and adequate light
12. decided to provide the user with the capability to stack flow rates i e to program a sequence of rates that will apply to successive patient administrations A number of questions arise Should flow rate retrieval and administration functions be automatic or manual What happens if one of the queued flow rates is accidentally deleted defaulting to the next flow rate How does the user identify and track the flow rates How does the user access and change a specific flow rate If such questions are addressed early in the product s development the answers will help Figure 7 Ventilator Alarm shape the functional design which in turn will help Control determine the user interface alternatives iJi up tr Some functional issues are complicated by medical practice operating conditions and the preferences of individual healthcare practitioners An example is the degree to which ventilator or anesthesia machine pressure limit alarm settings dele Cie ABE illustrated in Figure 7 should be under the user s control Many practitioners prefer a wide latitude in setting alarms However a very low alarm setting permits the user to effectively disable the alarm Safety implications should be carefully weighed against the user s preferences How much discretion should the user be permitted in setting limits In summary too many functions or too much littlle automation can be problematic depending upon the user population and working e
13. device not the users being tested If this is not made clear users may feel that their performance will be discussed with their superiors and thus they will not be forthcoming about errors and deficiencies related to interface design Also should a device be evaluated during actual use on patients data should be collected over a reasonable length of time not just a day or two In real 37 Do It By Design world settings actual problems often emerge slowly and require repeated observations for identification Findings may prove of great value to both healthcare facilities and manufacturers Final Comment There is much one can do to assess devices already in use as well as those being considered for purchase Let the manufacturer know of uncovered strengths and weaknesses Companies not only are responsive to their customers but they want to market medical devices that meet customers needs for functionality safety and effectiveness 38 Do It By Design APPENDIX Points to Consider In considering the need for and conduct of human factors analysis and testing there are a number of issues and questions to ask 1 Does the device require user interaction with respect to operation maintenance cleaning or parts installation If so do the technology and device functions permit alternative user interface designs 2 Given the combination of user interface user population and operating conditions are errors likely
14. easy installation and connection If properly designed incorrect installations should be impossible extremely difficult or so obvious that they can be easily detected and remedied Userinstructions should be understandable and warnings conspicuous e Ifa hazard cannot be eliminated by a design solution color codes or other markings will help the user achieve proper connections and component or accessory installation Positive locking mechanisms are desirable whenever the integrity of connections may be compromised by such factors as component durability motion or casual contact Protected electrical contacts e g the conductors are recessed are necessary for body leads that can be inadvertently introduced into outlets power cords extension cords or other common connectors If possible exposed contacts should be avoided e Components and accessories should be numbered so that defective ones can be replaced with the proper items 12 Do It By Design e Textual complexity in maintenance manuals should be reduced by adding graphics Summary There is a variety of device components and accessories Potential hazards should be identified and appropriate design and coding techniques should be used to prevent misinstallation ALARMS Alarms and related advisories are intended to alert device users about problems with the patient and device status This seemingly straightforward function often is complex In some en
15. or correction Also software related errors can be subtle For example users become frustrated by cumbersome data entry steps and make errors not directly related to those steps Ambiguous acronyms or abbreviations used in the command structure or on menus may also lead to serious errors Below are examples gathered from incident files recalls and analyses There have been incidents with radiation treatment devices because users failed to enter dosage levels if the device software did not prompt the user for Do It By Design the data Instead the device automatically defaulted to a given value without signaling this value A cardiac output monitor alarm was disabled without the operator s knowledge when the control buttons were pushed in a specific sequence There have been serious infusion pump incidents and recalls involving such deficiencies as poorly signaled operating modes cumbersome operating steps and the presentation of unanticipated warning data on displays normally reserved for other critical information Below are some general considerations that if implemented can prevent many software related design errors Rules of Thumb Do not contradict the user s expectation Rather exploit their prior experience with computerized equipment and consider conventions related to language and symbols Beconsistent and unambiguous in the use and design of headings abbreviations symbols and formats Always keep
16. or even death The application of user interface design principles and participation of healthcare practitioners in design analyses and tests are very important In addition to increased safety an added benefit of such practices is the likelihood that good user interface design will reduce training costs to healthcare facilities This document offers guidance intended to increase the understanding of human factors in device design The Center publishes the results of its work in scientific journals and in its own technical reports Through these reports CDRH also provides assistance to industry and to the medical and healthcare professional communities in complying with the laws and regulations mandated by Congress The reports are sold by the Government Printing Office GPO and by the National Technical Information Service NTIS Many reports are also available on the Internet World Wide Web We welcome your comments and requests for further information 2 eee KS R D Bruce Burlington M D Director Center for Devices and Radiological Health Do It By Design PREFACE Human factors is a discipline that focuses on those variables that affect the performance of individuals using equipment The subject of this primer is the impact of design upon safe and effective use of medical devices Errors in the use of such devices often are caused at least in part by the design of the user interface i e those features with which healthcare pra
17. user interfaces and the company s experience with predecessor devices In the unlikely case that a device has virtually no user interface or functional integrity precludes interface design options a substantial human engineering effort would not be warranted However most devices require substantial user device interaction and the complexity of the interface usually is an issue The greater the impact of errors upon the health and safety of patients the greater the need for thorough analysis and testing If the user interface is similar to that of a previous model the use history of the latter model and the potential impacts of any changes to the new model merit attention The Appendix offers points to consider regarding human factors engineering efforts ADVICE TO HEALTHCARE FACILITIES Recognizing human factors design problems with already purchased devices is important The selection of new equipment that staff can operate safely and effectively also is important This section deals with these issues Recognizing Problems Healthcare professionals are more likely to blame themselves for errors than they are to blame the equipment User interface flaws can be subtle and a physician s or nurse s attention is focused on the patient not the device Also a sense of professional responsibility often precludes healthcare practitioners from blaming the device as a consequence practitioners are often blamed for design induced errors Altho
18. users informed about current device status Provide immediate and clear feedback following user entries Design procedures that entail easy to remember steps Use prompts menus etc to cue the user regarding important steps do not strand the user Give users recourse in the case of an error Provide conspicuous mechanisms for correction and troubleshooting guides Do not overload or confuse users with information that is unformatted densely packed or presented too briefly Consider the use of accepted symbols icons colors and abbreviations to convey information reliably economically and quickly Do not over use software when a simple hardware solution is available e g a stand alone push button for a high priority time driven function 10 Do It By Design Consider using dedicated displays or display sectors for highly critical information In such cases do not display other data in these locations Summary Microprocessing offers outstanding capabilities ready data access manipulation computation speedy accomplishment of functions and information storage Technological sophistication however can work to the user s disadvantage if the software design is done without a thorough understanding of the user At a minimum designers are advised to utilize guidelines for human computer interface HCI do a thorough analysis and conduct usability testing during software development A thorough kno
19. usually will not be able to visualize design concepts in the abstract They react best to existing devices mockups or pictorial drawings of a device interface In the latter instance the operational logic should be clear Allowing people to react to something tangible will provide a wealth of ideas Questions such as those in Figure 6 can help target problems with design Interviewing Supervisors Trainers and Risk Managers Most healthcare supervisors have fairly broad views of device strengths and weaknesses They are aware of serious incidents and device characteristics that are substantial impediments to productivity Training staffs often have detailed knowledge of the effects of design on training time as well as recommendations for instructional manuals Risk managers document incidents that can shed light on specific design problems Interviewing Maintenance Personnel Maintenance personnel may have a unique perspective about device problems Users often bring to them broken devices that in fact are functional but difficult to use For example poor design for installation and examples of misinstalled componen ts may come to light In addition a damaged device may signal a user related problem Finally since recalled devices often are modified on site technicians will know of both hardware and software fixes related to deficiencies in the user interface Conducting Focus Groups Focus group sessions are group interviews of a few
20. valuable when assessed in conjunction with performance data and expert opinion Testing in the Real Environment The user interface should be tested under conditions that are as realistic as possible Participants should be reminded that it is the device not themselves being tested Simulating Actual Conditions in the Laboratory Some aspects of actual use conditions are relatively easy to simulate For example adjustable lighting and individual lamps of varying wattage and direction will produce variable levels of illumination and glare Likewise tape recordings from emergency rooms operating rooms and critical care facilities will reproduce decibel and frequency levels that challenge alarm audibility and the user s concentration With home use devices it is important to simulate environmental constraints e g space that pertain to such device characteristics as placement and portability It is more difficult to simulate patient and device status as well as the interactive effects of multiple devices In the monitor example changes in patient and device status could be simulated by programming in ECG changes and alarms In multiple device scenarios test participants might alternate between different devices they typically use on the job Variables might include conflicting user interface designs and problems associated with device attachments Simulations in Healthcare Facilities Even without patients performance testing in hea
21. x DNC An Introduction to Human Factors in Medical Devices By Dick Sawyer Office of Health and Industry Programs CDRH Work Group Kaiser J Aziz Office of Device Evaluation Cathy L Backinger Office of Surveillance and Biometrics Everette T Beers Office of Device Evaluation Andrew Lowery Office of Health and Industry Programs Stephen M Sykes Office of Science and Technology Alvin Thomas Office of Health and Industry Programs Kimberly A Trautman Office of Compliance U S Department of Health and Human Services Public Health Service Food and Drug Administration Center for Devices and Radiological Health Do It By Design FOREWORD The Center for Devices and Radiological Health CDRH part of the Food and Drug Administration FDA develops and implements national programs and regulations to protect the public with respect to devices and radiological health These programs are intended to assure the safety effectiveness and proper labeling of medical and radiation emitting devices An emerging concern of great importance to the Agency is the implementation of good human factors practices in the design of medical devices If device operation is overly complex or counter intuitive safe and efficient use of a medical product can be compromised Both CDRH databases and research findings indicate that lack of attention to human factors during product development may lead to errors that have the potential for patient injury
22. DFW Airport TX 75261 9616 Characterizing the Human Factors Effort Despite substantial variability in human factors engineering efforts the following are essential e a designated individual in the design effort who is responsible for user related issues participants from the user population requirements that the product be designed for safe use 34 Do It By Design studies analyses and tests that assess user performance and identify hazards and data indicating whether or not the user interface meets requirements The best advocate for the device user is someone who works integrally with the design team They participate in the planning and implementation of the appropriate studies analyses and tests Test participants can be drawn from the company s pool of clinical staff and outside healthcare professionals Potential hazards errors and broader usability issues normally are defined from device records user studies and analyses They will help shape initial requirements of the user which will be refined throughout development and will help determine the test criteria and measures Although there is no formula for deciding how extensive a human factors effort should be consideration of some basic variables will help in making decisions Weigh the following the nature of the user device interaction the user population and use environment the likelihood and criticality of errors the feasibility of alternative
23. FZ 230 1350 Piccard Drive Rockville MD 20850 For inquiries about the Quality System Regulation call Kimberly A Trautman Office of Compliance at 301 594 4648 This guidance is available through Internet World Wide Web at http www fda gov and after January 1997 from the National Technical Information Service Springfield Virginia 22161 telephone number 703 487 4650 Lireka P Joseph Dr P H Director Office of Health and Industry Programs Center for Devices and Radiological Health Do It By Design ACKNOWLEDGMENTS A wide range of human factors scientists engineers managers and healthcare professionals in FDA were invaluable for their contributions of time and expertise to this document The Agency acknowledges the following individuals for their efforts Marilyn Sue Bogner Mary W Brady Peter B Carstensen Robert J Cangelosi Art Ciarkowski John J Crowley James E Dillard William D Galloway Brenda A Hayden Ronald D Kay Patricia A Kingsley Michael C Long Bonnie H Malkin Donald E Marlowe Jack McCracken Susan K Meadows Michael Mendelson William H Midgette Gregory W O Connell Christine Parmentier Jay A Rachlin Cornelia A Rooks Walter A Scott Thomas B Shope Nancy Stade Barbara Stratmore Judy L Strojny Carol A Vetter and Catherine P Wentz Many thanks also to Donna Castner Nancy Lowe and Edie Seligson for their secretarial editorial and graphics support Finally a large numb
24. McGraw Hill Inc Sawyer D amp Lowery A 1994 CDRH s role in promoting user oriented design Medical Device amp Diagnostic Industry MD amp DI 16 3 72 82 Schneiderman B 1992 Designing the user Interface Strategies for effective human computer Interaction Reading MA Addison Wesley Spranger D M 1988 April Developing new products Meeting the users needs is the key to profits Health Industry Today 40 44 Van Cott H P amp Kinkade R G Eds 1972 Human engineering guide to equipment design Washington D C U S Government Printing Office Wiklund M E 1991 Usability tests of medical products as prelude to the clinical trial Medical Device amp Diagnostic Industry MD amp DI 3 7 13 7 68 73 46 Do It By Design Wiklund M E 1993 How to implement usability engineering Medical Device amp Diagnostic Industry MD amp DI 15 9 68 73 Wiklund M E 1995 Medical device and equipment design Buffalo Grove IL Interpharm Press Inc Wiklund M E Ed 1994 Usability in practice how companies develop user friendly products Cambridge MA Academic Press Woodson W E 1981 Human factors design handbook New York McGraw Hill 47
25. a fault condition such as air in or blockage of the infusion line and to activate an alarm Infusion pump cassette That part of the set of intravenous tubing that fits into an infusion pump Each cassette is dedicated or designed to fit a specific pump Iterative Prototyping Successive small scale tests on variations of a limited function prototype Such tests permit continual design refinements based upon human performance Interlock To prevent initiation of new operations until current operations are completed computer science To connect in such a way that no part can operate independently MedWatch Form 3500A A form that must be completed by user facilities and manufacturers to report device related adverse events to FDA under the medical device reporting MDR system 21 CFR Parts 803 and 804 Mockup Usually a full sized scale model of a structure used for demonstration study or testing 41 Do It By Design Negative transfer Transfer of training that results in increased likelihood of human error due to changes in the user interface or situations that are not obvious to the user Oxygen concentrator A device that produces a high concentration of oxygen 85 to 95 at clinically useful flow rates up to 5 L min by physical separation of oxygen from ambient air Oxygen concentrators are commonly used in home healthcare and occasionally in general anesthesia Screen print A static image represented on pa
26. aphic and device information are desirable When videotaping a session the tapes can be indexed by critical events and times in order to avoid a time consuming review Another issue is the sampling of participants and operating conditions Within the scope of time and resources available observing different users under varying work conditions is desirable to ensure the generality of the observations 21 Do It By Design Interviews Interviewing is a flexible way of obtaining opinions about specific devices problems and user preferences and ideas about improving user interface design Interviews also can be conducted quickly and in conjunction with observations Below are a few ideas about interviewing personnel in medical facilities Interviewing Users Healthcare practitioners and lay users often hold perceptions that differ greatly from those of the designer Valuable data can be obtained by having physicians nurses or home users do the following e walk through the operational steps Figure 6 Blood Glucose Monitor compare relative strengths and Display Messages weaknesses of different models Pa describe critical incidents involving ii SEI EE a device ERES i ee RUD Labels ifneeded recommend device changes and Are displays and labels legible Are strips easy to clean and insert Is device compact and durable How difficult are timing operations assess a new device concept Remember that interviewees
27. ase deliberate actions by the user do not occur DC Defibrillator A device that delivers an electrical shock for defibrillating restoring to normal heart rhythm the atria or ventricles of the heart or to terminate other cardiac 40 Do It By Design arrhythmias The device delivers the electrical shock through paddles placed directly across the heart or on the surface of the body Enteral Feeding Tube A tube for passing of food or medicines into the stomach Function The action or accomplishment intended of a system where the system consists of a device and a user Alternatively individual primary functions such as installation maintenance operation and monitoring are needed to accomplish the intended use of the user device system Guide wire A catheter guide wire is a coiled wire that is designed to fit inside a percutaneous catheter for the purpose of directing the catheter through a blood vessel Human Factors In the broadest sense a discipline devoted to the effects of user interface design job aiding and personnel training in the operation maintenance and installation of equipment Heart valve leaflets Any of the leaf like flaps of the bicuspid or tricuspid valves of the heart Infusion pump A device used to pump fluids into a patient in a controlled manner The device may use a piston pump roller pump or a peristaltic pump and may be powered electrically or mechanically The device may include means to detect
28. ces and viable alternatives for new designs ANALYSES Analyses of functions tasks and hazards are important to good design and will help shape the user interface by providing information about e user requirements and usability goals other devices in the users environment bottlenecks to potential performance and error inducing factors possible hazards device impact on user training and device operating logic Analyses merit careful attention and should be woven into the development process Functions and Tasks The user and a finished device work together as a system Primary functions are device installation maintenance operation and monitoring The user s functional 23 Do It By Design contributions are referred to as tasks Increasingly devices are multi functional in order to accommodate a wider range of users and to increase the flexibility of applications of the device Such increased capability can impede ease of use unless the respective assignments of functions to the device and tasks to the user are carefully weighed Machines are good at storage and retrieval of coded data rapid computation timing and deductively based activities People perform better in sensory judgmental interpretative and non routine tasks The number of functions and relative device user allocations have important implications for the user interface As a hypothetical example suppose that an infusion pump designer
29. cessfully perform functions and extract information during operation of a device especially during critical events The next section discusses the logic of such user device interactions DEVICE LOGIC AND MICROPROCESSING With modern automation the logical temporal and informational characteristics provided via software are increasingly crucial and error inducing For instance data presented imprecisely ambiguously or in a difficult to read format are likely to be misread Examples are crowded CRT displays cryptic abbreviations or time lags between user input and displayed feedback Such design may overtax the user s memory and decision making capability Characterizing the Shift to Software With a large number of controls and displays the user must identify and integrate spatially disparate information Although such designs are still common the trend is to assign more functions to software This reduces the number of controls and displays but it can increase the burden on the user in other ways This is the case with with many infusion pumps as shown in Figure 2 on the following page Although there are few controls and displays the large amounts of information impose heavy demands on the user s memory Most information must be recalled in sequence thereby precluding simultaneous viewing of related data Users can become lost in the system if sufficient prompts and roadmaps are absent Also users may misinterpret displayed data and
30. ctitioners and lay users interact Mistakes made during device operation not only can hamper effective patient treatment monitoring or diagnosis but in some cases can lead to injury or death It is important that medical devices be designed with consideration of the impact of design on safe use This primer discusses human factors problems general design principles and human factors engineering methods and uses examples and illustrations for clarification The Food and Drug Administration FDA believes that this information is important because of its implications for patient and user safety Reports received throughout the Medical Device Reporting MDR system recall data and other postmarket information indicate that device design and related use errors are often implicated in adverse events As implied in the language of the design control section of the Quality System Regulation design requirements relating to a device are appropriate and address the intended use of the device including the needs of the user and patient human factors is an important consideration in quality assurance programs Additionally good human factors design is an important consideration in submissions to the Agency prior to device marketing While this guidance represents a final document comments and suggestions about Do It By Design may be submitted at any time for Agency consideration by writing Dick Sawyer Office of Health and Industry Programs H
31. d homes Performance often is compromised by noise poor lighting glare producing surfaces heat dirt improper cleaning products electrical interference humidity and moisture Poorly written procedures stress and fatigue can also degrade performance Compounding the situation is the wide array of equipment that a healthcare practitioner operates A medical device can be used safely and effectively only if the interaction between the operating environment user capabilities stress levels and device design is considered when the manufacturer designs the device The following dimensions of human capability are basic to an understanding of human factors Physical and Sensory Characteristics A person s most basic physical and sensory capacities include vision hearing manual dexterity strength and reach A number of related design factors can interact with them to influence human performance the legibility and discriminability of displayed symbols audibility and distinctiveness of alarms the strength required to make connections and the requirements for reaching controls Perceptual and Cognitive Abilities Perception is the ability to detect identify and recognize sensory input Understanding human limitations and exploiting human strengths in this area is crucial for safe design of equipment Perceptual characteristics are important in the design and arrangement of controls keypads displays information presentation and alarms
32. de to usability testing Norwood N J Ablex Publishing Corporation Emergency Care Research Institute ECRI 1992 Critical alarms Patients at risk Technology for Critical Care Nurses 2 1 1 5 Fischer S C Blowers P A amp Bakowski L S 1993 Using FDA recommendations to develop and test a home user manual Medical Device Diagnostic Industry 15 11 110 114 Gopher D M Badihi Y Cohen G Donchin Y Bieski M and Shamay C 1989 October The nature and cause of human errors in a medical intensive care unit Proceedings of the 33rd Annual Meeting of the Human Factors Society October 1989 Denver CO Human Factors Society Helander M Ed 1991 Handbook of human computer interaction 2nd Edition Amsterdam North Holland Henriksen K Kaye R D Jones R Morisseau D S amp Serig D I 1995 Human factors evaluation of teletherapy Summary and prioritization of issues Volume I NUREG CR 6277 Washington D C U S Nuclear Regulatory Commission Horton W 1990 Designing and writing online documentation New York John Wiley and Sons Inc Hyman W A 1988 Human factors in medical devices In Webster J G Ed Encyclopedia of medical devices and instrumentation Vol 3 pp 1542 1553 New York Wiley Karat C 1992 Cost justifying support on software development projects Human Factors Society Bulletin 35 11 Santa Monica CA Human Factors Society Kelly R T
33. de tube to serve as an injection site and hollow spike to penetrate and connect the tubing to an I V bag or other infusion fluid container Anthropometry The field that involves the measurement of the dimensions and other physical characteristics of people and the application of this information to the design of things they use Blood glucose monitor A device that quantitatively measures glucose concentrations in the blood Calibration To check adjust or standardize systematically the graduations of a quantitative measuring instrument Cardiac monitor including cardiotachometer and rate alarm A device used to measure the heart rate from an analog signal produced by an electrocardiograph vector cardiograph or blood pressure monitor This device may sound an alarm when the heart rate falls outside preset upper and lower limits Catheter A tubular medical device for insertion into canals vessels passageways or body cavities usually to permit injection or withdrawal of fluids or to keep a passage open Coding Identifying objects or events with the use of recognizable symbols typically visual or auditory utilizing readily apparent variables such as color shape size direction pitch or duration Cognition Processing information about the environment and oneself in conscious intellectual activity as in thinking reasoning remembering and imagining Default Parameters that are automatically selected by a machine in c
34. e familiar with the monitor the test team might have them run through the operations at their own pace at any point probing with questions about bottlenecks or apparent 30 Do It By Design problems If critical issues arise the test can focus on these and less on others In addition because devices are often used in very intensive novel situations users can be stressed by minimizing their familiarization with the device and limiting the use of instruction manuals which often are not readily available in real world situations Also consider the possibility of testing novice device users in order to impose a greater burden on the interface Possible performance measures in the sample scenario include set up times number of errors type of errors changes in error raters failures to detect and discriminate alarms task completion time and any observations that indicate performance obstacles In addition if the participants are asked to think aloud as they proceed through the tasks it is important to develop a record of their remarks Finally pre and post testing questionnaires or interview comments likes and dislikes about user interface elements and other comments about overall device safety and usability are valuable One caveat however is that users generally are inexperienced with design principles Although their opinions generally are valuable the subjective preferences of device users for various interface designs are most
35. ecdotal reports or comments asampling of the user population with respect to individual differences ideas for new designs and reactions to design concepts and information necessary for establishing performance test protocols and performance criteria Early studies along with document reviews and task analyses are very important They engender creative thinking and reduce the likelihood of major mistakes in the design process Study Methods Below are some techniques frequently used in early studies They are not independent of one another and techniques discussed elsewhere such as task analysis may also be integrated into these approaches Observations In a medical facility the operating rooms emergency rooms and critical care units are fertile areas for observational studies of associated devices These include the observation of ongoing operations and the inspection of devices following operation especially after prolonged use There are implications for areas such as maintenance cleaning installation and the effects of environmental conditions upon the user interface In the operating environment substances such as dirt water saline solutions alcohol blood and coffee often impede proper use of a device as well as its functioning Non intrusive and systematic observations are best They can be recorded as narrative descriptions and or as entries on data sheets formatted with predetermined data categories Demogr
36. ecial interest and interviewed after the completion of procedures Likewise observations by trained observers are valuable Field Studies Studies of devices already in use offer an excellent opportunity to obtain valuable information once a device is marketed Because there are few time constraints data can be obtained from a wide variety of settings and user groups Such studies can be modified at any point to accommodate changing circumstances The findings will supplement and clarify complaint data as well as provide unanticipated information pertinent to marketing and new development efforts This data should be documented for current and future use Summary Obtaining performance data from actual users is crucial If test participants cannot safely and effectively use a device under test conditions healthcare professionals definitely will have problems with it under actual conditions of use Finally the development of user requirements and thorough testing helps ensure that the final product addresses the needs of healthcare professionals and patients 32 Do It By Design SPECIAL ISSUES INITIATING A COMPANY HUMAN FACTORS PROGRAM Personnel No two product development projects are identical and the same can be said of corporations Size organization and culture vary from firm to firm all will affect the implementation of a human factors program Whether relying primarily on consultants or staff experienced with human factors engi
37. ent and military agencies are useful Complaints and Recall Data A company s recall and device experience data can provide historical information that may lead to important insights about potential problems and design solutions relevant to new product development Reports in FDA s MDR system about problems across a device area may also be enlightening Although use errors and design traditionally have been treated as separate issues one can glean substantial information from this source via careful analysis Such information may identify potential problems during the feasibility phase of a new development project Guidelines Guidelines provide principles data and human factors engineering methods An example of a principle might be the following There usually should be feedback displayed immediately following a user input via a control key switch or other input device Data may include anthropometric dimensions visual and auditory limits etc The most widely recognized guidelines in the medical device community are the ANSI AAMI Human Factors Engineering Guidelines and Preferred Practices for the Design of Medical Devices 1993 Other guidelines published by government agencies include guidelines and military standards They contain useful information about principles and methodology Many textbooks on human factors usability testing and human computer interface HCI design also are applicable Guidelines must be used judiciou
38. er of professionals with universities healthcare facilities human factors and design firms and the medical device manufacturing community provided a great deal of expertise and support We are unable to acknowledge them individually but wish to thank them for their time and effort Do It By Design TABLE OF CONTENTS PORWARO 262222605056 Pa Eiin Obese Couns E AAE a ketenes onere kieed ii PIREFAGDE o RE ERES aae eee eevee a Ra as Red bau ee eek ees eae iii ACKNOWLEDGEMENTS 2322 dra Ck CHEER Ro Det ed a aae pel pee iv NTRODUC TION serpi dub REPRE ERE RIS S EuEEY ERI m n ERR qe Reds 1 HUMAN FACTORS AN HISTORICAL PERSPECTIVE ieeseeeeesse 2 WHY HUMAN FACTORS ENGINEERING IS IMPORTANT ln 3 The Interaction of User characteristics and the Operating Environment 3 Physical and Sensory Characteristics llle 3 Perceptual and Cognitive Abilities 0 0 0 eee ee 3 MOMCAUSE cues redes que sire aeg yew edes Sead po Bea Eo geehrt se e aC E 4 Design Inmplicaupns s icr mca rend aure x RE EUR E PEE TERR TOS EE e Es 4 THE USER INTERFACE 0000 rs 6 Control Display Arrangement and Design l l 6 Examples of errors related to hardware design 000 eee eeuee 6 Rules OF Tub oie den cee sd RE RIDES ERR xe ERE GA RAE GA REEE 7 SUMMON ovoid ades ductus Earn e EI d Enklndi a oped eine dedo qe ERA d qupd Ene 8 a 8 Characterizing the shift to soft
39. erface design is critical to safe and effective equipment operation installation and maintenance Human factors should be considered early in the design process and systematic analysis and hands on testing should be conducted throughout development stages and involve participants from the end user population It is not simply a matter of fine tuning Thorough attention to design will result in safer more usable devices and correspondingly fewer accidents reduced training costs fewer liability problems and less trial and error during device development Because poor user interface design greatly increases the likelihood of error in equipment operation Do It By Design encourages readers to think critically about the impact of device design upon the ability of healthcare professionals to treat patients safely and effectively On a positive note attention to human factors design principles and methods will help greatly in the development of a product that meets the users needs Consider this primer a starting point One should supplement this information with more detailed data principles and methodologies from guidelines standards texts and articles some of which are listed in the References for Further Reading Do It By Design HUMAN FACTORS AN HISTORICAL PERSPECTIVE Human factors is a discipline that seeks to improve human performance in the use of equipment by means of hardware and software design that is compatible with the ab
40. ern depending on the type of device and target population With home use devices participants should be sampled from the lay user population In some cases the effects of medication should be considered provided that safety and ethical standards are met Conducting the Test Below is a scenario that might be used in a fairly comprehensive assessment of the user interface design of the arrhythmia monitor It consists of narrative that requests the participants to perform various tasks This will help the test team obtain data on errors performance times and impressions of device design features Evaluation of the data will answer the kinds of questions listed under the monitor in Figure 9 The participants might be given instructions such as the following Figure 9 Monitor Interface ee ee pe aera reas Are alarms distinctive and obvious waveforms accessible and clear and screens and menus well formatted What is the likely impact of the user interface on training requirements Turn on the monitor and perform the basic setup tasks such as checking and adjusting the calibration amplitude gain and alarm limits When prompted retrieve waveforms and trend data as specified Report any visual alarms such as disconnected lead wires or a low battery Generally the device users selected as test participants should be healthcare professionals who are not trained on the specific model After participants becom
41. ethods are useful in multi task situations which involve the use of more than one device by the user Summary Thorough and continuous analysis is a powerful tool and is necessary throughout the design process Overall the findings can be combined with drawings diagrams user profiles and various other data summaries to help shape alternative user 27 Do It By Design interface designs elucidate flaws in design and provide the focus for human factors tests USABILITY TESTING Testing for ease and accuracy of use is the only way to ensure that users can safely and effectively operate install and maintain devices By means of iterative prototyping individual concepts of design can be tested refined and retested throughout the development process This process culminates with full testing of a model embodying all the user interface characteristics for both hardware and software of a fully functioning device Developing Prototypes Prototypes simulate the user interface as defined by both the hardware and software they are used to select alternative designs and uncover problems A prototype s fidelity or resemblance to a working device is determined by it s physical and or conceptual attributes If installation control and display layout or manual operation e g of surgical tools are of special interest mock ups should be used for physical simulations or games playing Users can perform the procedural steps to co
42. ethods sad ace concha ou tee Peas SEEK eee T CRURA 21 loc TID 25640446 bo epee ded wh EM E a a aa etn h heen E 21 Hil SE VIBWS uris tare ere 3 a enue ab cau STRE 6 ud wh eS ee 22 Conducting Focus Groups Sess d ce See honest ewe O86 Heed X EO 22 Physical Measurements sse 23 SUMMONS sacs bovechee tice XR pE bec bed e We eR ERE seeds 23 EEEE T E E TEES 23 Functions and Tasks os 5 ewes aaa aaaea 23 Analyzing TaSkS Loux xceseer x RERERSAR GS aids soca babe ide 24 Hazard ABdlySes 2cici lt eres bonu aedes dus oa cx bli Er m P M api ae 27 Other Analyses MET 27 SUMMATY carea e e REER LITT oL EER EE E EE R 27 NM 28 Developing Prototypes x uesesite nprekewesestibkerq EE RR REMES RES 28 Developing Scenarios sellsiseeeeeeeeeesr eee 28 Requirements and Measures 000 cc eee eee eens 29 Facilities csists teeters bead a ea eee ieee Shwe bd REE RG 29 Fest Participa tS s CPT 30 Conducting the Test 2 0 55 eee ees 30 Testing in the Real Environment 00002 cee ee eee eee 31 Simulating Actual Conditions in the Laboratory 31 Simulations in Healthcare Facilities ills 31 Simulations in Homes 0 00 cece cece eee 32 CGlm al Trials 24 3 3 b hr R E CERE dE be ede dca dash CECI Ro 32 Bud sisie seia rm 32 SUMMA A TC LC E EEE E EEE i AEE EE a eE 32 Do It By Design SPECIAL ISSUES 22 5cc5so6seeedsie bebe EE
43. idents or near misses can be a warning especially if there are highly competent individuals involved When questioning staff and examining implicated devices look for types of problems mentioned above The December 1995 coding manual for Medical device reporting using mandatory MedWatch FDA Form 3500A contains a number of codes having implications for user interface design These are found under the Device Related Terms Results of Evaluation Codes and Conclusion Codes They are valuable not only for device reporting purposes but also for sensitizing staff to important human factors design issues Evaluating Devices Before Purchase Before buying a new model consider the means of assessing its usability especially if it is a life sustaining or life supporting device Following are some steps to consider Determine whether or not the manufacturer conducted human factors usability testing of the device in question Check with staff and possibly other facilities about predecessor models made by the manufacturer e Check with other facilities that may also be using the new model Check published evaluations of the new model Request a trial period prior to the actual purchase of a new device Analyze and Test the Model When doing analyses and tests on devices being considered for purchase or already in use there are a few guidelines to keep in mind Be careful not to bias the users Staff should be told that it is the
44. ilities of the user population The terms human engineering usability engineering and ergonomics are often used interchangeably for the process utilized to achieve highly usable equipment Historically human factors can be traced to early efforts by industrial engineers psychologists and efficiency experts to streamline manufacturing operations and equipment for better worker efficiency In World War II emphasis shifted from production to personnel safety A special focus was cockpit design of aircraft Poor design of controls and displays often induced pilot errors sometimes leading to crashes Human factors analyses and tests became routine in the design of military and commercial cockpits Through the 1970s the most notable applications of human factors were highly costly complex systems regulated by the Federal government such as military and transportation systems Media coverage of user related accidents like the Three Mile Island nuclear power plant meltdown has done much to increase the recognition of human factors Such disaster stories are by no means a thing of the past Recently a nationally aired television program presented findings related to a disastrous airline crash The investigators concluded that difficult to distinguish operating modes of the guidance system and confusing data displays misled the pilots They thought they were viewing angle of descent information when in fact they were viewing vertical drop
45. in altitude data The plane crashed short of the runway without the crew attempting corrective action Human factors principles increasingly are being applied to commercial products Examples include ergonomically designed automobiles and the development of user friendly computer hardware software and communications products Although some manufacturers now integrate human factors design into their medical devices there exists a need for more widespread applications Do It By Design WHY HUMAN FACTORS ENGINEERING IS IMPORTANT Design induced errors in the use of medical devices can lead to patient injuries and deaths A user s behavior is directly influenced by operating characteristics of the equipment user interfaces that are misleading or illogical can induce errors by even the most skilled users A brief discussion of device users operating conditions adverse events and design implications will show the need for medical device designs that accommodate the necessary range of user capabilities THE INTERACTION OF USERS DESIGN AND OPERATING ENVIRONMENT Healthcare practitioners vary greatly in their physical sensory and mental abilities Lay people who represent an increasing proportion of medical device users are even more variable Medical devices are used in many environments including operating rooms emergency rooms patient units x ray departments laboratories emergency vehicles critical care facilities clinics an
46. in the breathing gas 42 Do It By Design REFERENCES FOR FURTHER READING Standards Association for the Advancement of Medical Instrumentation 1994 Human factors engineering guidelines and preferred practices for the design of medical devices ANSI AAMI 1994 Arlington VA AAMI American National Standards Institue 1988 American National Standard for human factors engineering of visual display terminal workstations ANSI HFS 100 1988 New York ANSI American National Standards Institute 1991 Safety Color Code ANSI Z535 1 1991 New York ANSI American National Standards Institute 1991 Safety color code ANSI Z535 1 1991 New York ANSI American National Standards Institute 1991 Criteria for safety symbols ANSI Z535 3 1991 New York ANSI American National Standards Institute 1991 Product safety signs and labels ANSI Z2535 4 1991 New York ANSI American Society for Testing and Materials 1988 Minimum performance and safety requirements for components and systems of anesthesia gas machines ASTM F1161 1988 Philadelphia ASTM American Society for Testing and Materials 1990 Ventilators intended for use in critical care ASTM F1100 1990 Philadelphia ASTM American Society for Testing and Materials 1993 Standard specification for alarm signals in medical equipment used in anesthesia and respiratory care ASTM F1463 93 1993 Philadelphia ASTM International Electrotechnical Comm
47. in ways that others would not anticipate Resources Some resources already have been discussed the literature guidelines and expertise of current staff Many manufacturers may also need a consultant s help in establishing a human factors program There are many highly qualified human factors consultants available for such purposes They currently apply their expertise to areas ranging from military systems air traffic control and nuclear power plants to office equipment and increasingly medical devices The basic rationale and methodology is the same in all of these areas The societies listed below are clearing houses for consultants Ergonomics Society University of Technology Loughborough LEIC LE11 3TU England 33 Do It By Design Human Factors and Ergonomics Society HFES P O Box 1369 Santa Monica CA 90406 IEEE Systems Man and Cybernetics Society 345 East 47th Street New York NY 10017 Industrial Designers Society of America 1142 E Walker Road Great Falls VA 22066 Society for Information Display 8055 W Manchester Avenue Suite 615 Playa del Rey CA 90293 Society for Technical Communications STC Suite 904 901 North Stuart Street Arlington VA 22203 Special Interest Group on Computer and Human Interaction SIGCHI Association for Computing Machinery P O Box 12115 Church Street Station New York NY 10249 Usability Professionals Association American Airlines STIN P O Box 619616 MD 4230
48. ine to create potentially dangerous situations Rules of Thumb e Consider the wide spectrum of operating environments when designing and testing alarms including other equipment in simultaneous use 13 Do It By Design Be sure that visual and auditory alerts and critical alarms are included in the design requirements for the device Carefully consider the effects of over sensitivity electromagnetic interference and static electricity on alarm functioning Design alarms so they meet or exceed normal hearing and visual limits of the typical user Make sure that both brightness contrast and color contrast are sufficient for legibility under a variety of lighting conditions Use codes such as color that correspond to established conventions Design alarms to be distinguishable from one another and to the extent possible from alarms on other devices used in the same setting Design alarms to activate immediately following the onset of a critical problem It is important that alarms identify the source of the problem Consider giving a priority status to critical alarms Critical alarms should provide redundant auditory and visual signals Design alarms so that when they are silenced they remain silent temporarily They ideally will have visual indicators to indicate status and a mechanism for querying the reason for the alarm OTHER IMPORTANT ISSUES Dimensions Forces and Angles Workstations seating
49. ing An increasingly elaborate setup would include a one way mirror observation room video camera s adjustable lighting tape player for noise presentation an automated data logging system a microphone and other medical equipment Finally testing in medical facilities is another possibility 29 Do It By Design Test Participants In the case of small iterative prototype evaluations conducted throughout development two or three participants per test may be sufficient Employees such as Clinical staff may be used although repeated use of the same individuals can bias the findings Full usability tests require larger samples drawn directly from the user population If a device is intended for a fairly homogenous population data obtained with about 10 individuals representative of that population may be sufficient to eliminate most problems However it is important to note that the cumulative number of participants over the course of development can be substantial given the iterative small tests mentioned earlier In general the test team should consider the extent to which additional problems are uncovered as more participants are added and or as more tests are run Witha more heterogenous population or in competitive device testing larger samples are desirable The user interface can be maximally stressed by using new healthcare practitioners However the preexisting habits of experienced individuals also may be an important conc
50. ion in this document viii Do It By Design INTRODUCTION The purpose of this primer is to encourage manufacturers to improve the safety of medical devices and equipment by reducing the likelihood of user error This can be accomplished by the systematic and careful design of the user interface i e the hardware and software features that define the interaction between users and equipment This document contains background information about human factors as a discipline descriptions and illustrations of device problems and a discussion of human factors principles and methods In addition the final section of this document contains recommendations for manufacturers and healthcare facilities The primer is directed to the following audiences Manufacturers Employees of the Food and Drug Administration FDA Healthcare professionals Because many designers engineers scientists and healthcare professionals may be unfamiliar with human factors this primer is written as a basic educational tool and assumes little background in the subject At the same time much of the content may serve as a resource for those individuals who have had experience with human factors issues The information in this document will be useful in planning human factors programs that involve testing incident analysis or staff training In addition to providing technical information it also discusses various human factors resources Good user int
51. ission 1988 Graphical symbols for electrical equipment in medical practice IEC 878 1988 Geneva Switzerland National Committee for Clinical Laboratory Standards 1996 Laboratory instruments and data management systems Design of software user interfaces and end user software systems validation operation and monitoring NCCLS GP 19 P Villanora PA NCCLS 43 Do It By Design U S Department of Defense 1991 Anthropometry of U S military personnel DOD HDBK 743A Washington D C DOD U S Department of Defense 1992 Human engineering design criteria for military systems equipment and facilities MIL STD 1472D Washington D C DOD Textbooks Reports amp Articles Backinger C amp Kingsley P 1993 Write it right Recommendations for developing user instruction manuals for medical devices used in home health care HHS Pub FDA 93 4258 Rockville MD U S Department of Health and Human Services Food and Drug Administration Bailey R W 1989 Human performance engineering using human factors ergonomics to achieve computer system usability 2nd Edition Englewood Cliffs Prentice Hall Bias R amp Mayhew D 1994 Cost justifying usability Cambridge MA Academic Press Bogner M S Ed 1994 Human error In medicine Hillsdale NJ Lawrence Erlbaum Associates Brennan T A 1991 Incidence of adverse events and negligence in hospitalized patients Results of the harvard medica
52. l practice study New England Jounel of Medicine Vol 324 No 6 Brown C M 1989 Human computer interface design guidelines Norwood NJ Ablex Publishing Company Callan J R amp Gwynne J W 1993 Human factors principles for medical device labeling San Diego CA Pacific Sciences amp Engineering Group Callan J R Kelly R T Gwynne J W Muckler F A Saunders W M Lepage R P Chin E Schoenfield amp Serig D I 1995 Human factors evaluation of remote afterloading brachytherapy function and task analysis NUREG CR 6125 Vol 2 Washington D C U S Nuclear Regulatory Commission Cangelosi R Carstensen P Crowley J et al 1989 An analysis of medical device related reporting of anesthesiology related deaths Rockville MD Food and Drug Administration Internal Report Carstensen P 1986 FDA Issues Pre Use Checkout Anesthesia Patient Safety Foundations Newsletter 1 13 17 44 Do It By Design Cook R I Woods D D Howie M B Horrow J C amp Gaba D M 1992 Unintentional delivery of vasoactive drugs with an electromechanical infusion device Journal of Cardiothoracic and Vascular Anesthesia 6 2 238 244 Dray S M amp Karat C 1994 Human factors cost justification for an internal development project In Bias G amp Mayhew D J Eds Cost justifying ssability pp 111 122 Boston Academic Press Dumas J amp Redish J C 1993 A practical gui
53. lets Originally cotton was used to accomplish this separation but in a number of instances surgeons had neglected to remove the cotton spacer prior to installing the heart valve There were several deaths due to the formation of massive clots associated with residue from the cotton The integral spacer precludes such accidents Summary Implicit in the discussion of errors is the importance of implementing good design principles Rarely do human factors principles fully cover all design situations Good design practice entails the involvement of medical device users in studies analyses and tests to achieve optimal design The next section on human factors engineering discusses these methods 16 Do It By Design HUMAN FACTORS ENGINEERING Human factors engineering is a methodology that is crucial to effective user interface design it entails the iterative application of various procedures and tools throughout the design cycle as illustrated in Figure 5 Participation of individuals from the user population is integral to this process The developers of high technology products have adopted and refined such methods calling their approach usability engineering Of particular note is their emphasis on user studies and computerized testing prototypes Figure 5 Human Factors Engineering Process Conduct Develop Analyze Design Perform Develop Exploratory Concept amp Tasks User Usability Final Studies Requirements Hazards a
54. lthcare facilities adds substantial realism If on duty physicians and nurses are tested on devices that effectively simulate device interfaces and functions the effects of stress and fatigue on use of the device can be assessed especially if the tests are conducted at the end of shifts Testing in emergency rooms operating rooms or 31 Do It By Design critical care facilities is difficult if not impossible Testing in many cases should be performed during breaks and be limited to especially problematic design issues The exception would be a study in which a medical team performs a lengthy simulated procedure Then the facility essentially becomes a laboratory Simulations in Homes Medical devices intended for home use should be tested in that environment This can be especially useful in assessing devices that pose problems associated with space portability availability of electrical outlets lighting noise and operational complexity Lay users should participate if possible Clinical Trials Ideally one could do full testing during clinical trials however there are definite limits First manipulating the healthcare practitioner s behavior by running scenarios would be disruptive and could endanger patients Second the user interface design should be at least adequate prior to clinical trials However these factors do not preclude additional evaluation at this stage Physicians and nurses can be alerted to design issues of sp
55. mp Interface Tests Specification Functions j Resources amp Tools Literature Device Users Drawings Guidelines Subject MatteiExperts Mock Ups Device Data Consultants Predicate Devices Storyboards Prototypes Usability Labs Medical Facilities The rationale embodied in Figure 5 may be characterized as designing in the user Designers usually are too familiar with and too close to their designs to understand all of the potential impacts upon users Early consultation with the user population is necessary for assessing needs and developing requirements Users also are critical for analytical work and testing throughout product development With marketed products field testing and feedback to manufacturers are highly desirable Ideally hardware and software designers engineers human factors practitioners document writers and clinical staff coordinate their efforts to achieve a user interface design that lends itself to safe device assembly installation operation and maintenance The following factors will influence the flow of a given project pre existing data complexity of the device criticality of errors human factors expertise 17 Do It By Design experience with other devices similarity of a product to an existing one organizational culture and competitive market pressures When developing a device that automates previously manual tasks o
56. ne might start by analyzing the performance of such tasks by healthcare professionals in a clinical setting A competitive benchmark test of already marketed models also might be conducted to uncover strengths and weaknesses of existing designs Or a project could start with an examination of existing devices and manuals for design modifications markings or notations These may indicate that users attempted to compensate for design deficiencies Sometimes a new design represents a small departure from an existing one as in many product improvement efforts However even small hardware or software changes may have substantial impacts on the user interface Therefore potential impacts of change are important even when the use history of the predecessor device is indicative of good design Although there is latitude with respect to what analyses tests and tools are implemented the process should not be haphazard The rationale for human factors engineering lies in the repetitive analysis testing and refinement of design concepts all with input from users There is some trial and error but the bigger problems are detected and eliminated during the earlier stages before the design is frozen Finally information collected during these efforts can help reduce errors time and costs in future projects involving similar products The development of an in house human factors guidance notebook for a family of devices should be considered
57. neering integrating them into project design teams is crucial Educating both technical and managerial staff about human factors also provides long term benefits to the organization The target audience for training should include engineers designers manual and training developers risk managers quality managers and corporate executives Staff should know what a human factors program is and why it is important One should consider having a human factors professional give seminars which would include one or more of the following 1 discussion of human factors principles problems and methods 2 demonstrations or 3 case studies Involving a company s own designers and products will greatly increase the effectiveness of seminars Likewise the first hand experience of human factors practitioners with development efforts design principles liability issues and the literature is valuable There also are established professional short courses in human factors and many universities offer degree programs in this discipline There is a caveat however casual armchair approaches do not work training and experience are necessary Effective human factors programs consist of ongoing training that provides feedback for continuous improvement Finally depending on the manufacturer s capabilities and corporate resources management should consider hiring human factors staff Trained human factors practitioners can expand solutions to problems
58. nfirm or repudiate the design or layout details If underlying machine logic and information presentation are of concern story boards screen prints interactive computer models and working models can be used to evaluate user efficiency with a given interface design An early test might consist of users completing tasks by performing data entry operations on a sequence of screen prints The test participants would indicate their selected keys while verbally describing each action Each user input is followed by the presentation of a new print showing the appropriate feedback prompts or status change With more sophisticated computerized prototypes key panels and controls are represented graphically on a computer with the program having limited functionality Thus for example a finger press on a specific button simulated on a touch screen results in apparent button movement followed by displayed feedback The program then sets up the contingencies for the next operator response Horizontal prototypes present an overview of top level features but do not permit much operational depth Vertical approaches allow more in depth operation of fewer functions and greater data access Scenario prototypes combine features of both approaches allowing test participants to perform a limited number of tasks of particular interest at a given point in development Based on the findings the design is refined and the prototype is then retested Such p
59. nt important Transfer of Training Product developers often are encouraged to design products that incorporate unique distinctive features These can have performance and training impacts upon users in hospital units where physicians and nurses have become accustomed to a particular device model For example if two models have very similar look alike user interface configurations but require conflicting operator actions habits established with one device can interfere with user performance on the other This greatly increases the likelihood of errors For example if the ON OFF switch positions are reversed on two very similar devices a user transferring from one to the other could easily revert to the switch operation habits learned with the first device The same concern applies to a device that is retrofitted or redesigned This discussion is not intended to discourage innovation but rather to encourage designers to carefully evaluate the impact of user interface changes on user performance Device Maintainability Medical devices should be designed for simple maintenance because poor maintenance can hinder safe reliable operation Maintenance personnel often encounter the following problems e poor component labeling coding or numbering inadequate self diagnostic capability e parts that are hard to locate visually or by touch Screws and other parts that are difficult to reach or manipulate confusing compone
60. nt arrangements 15 Do It By Design requirements for difficult to find tools inadequate design for easy cleaning and materials that are not durable and degrade the user interface Possible signs of inadequate attention to human factors include improperly connected wires stripped threads unreliabe operation dirty displays and sticking keys Not only are devices that are difficult to maintain usually out of use for long periods of time but maintenance personnel may modify the devices to compensate for deficiencies possibly creating new problems for the user Device Packaging Packaging sometimes affects operation of a device For example there have been incidents resulting from packaging materials enclosed in such a way that users failed to detect and remove them In some cases this impaired functioning of the device With one infusion pump serious accidents occurred when unremoved packaging materials increased flow rates On the other hand packaging also can be designed to facilitate removal of devices or accessories and or to make storage easier Sometimes package design can reduce the likelihood of error For example catheters and compatible guide wires usually are packaged together The same is true of needles and syringes some infusion pumps and dedicated administration sets and various contact lens accessories A unique example is a customized container cover having an integral spacer that separates heart valve leaf
61. nvironment The appropriate tradeoffs should be considered at an early stage in the evolution of the design concept Analyzing Tasks Task analysis is critical to good human factors engineering and can be performed throughout the development phase At various points the design team should perform detailed sequential analyses of those tasks that comprise assembly installation operation and maintenance In the early conceptual stages critical tasks can be identified and described by observing and or questioning healthcare professionals who use the type of device under development When design concepts are initially formulated the analyses should be conducted as paper and pencil exercises As 24 Do It By Design development progresses analyses can be performed with such tools as device descriptions drawings existing devices and prototypes There are many methodological variations but task analysis is basically straightforward Depending upon the scope and purpose the analyst usually will do some or all of the following list the major tasks such as calibration entering operating parameters attaching the device to patient and cleaning parts describe the necessary information for each task user actions required decisions and related accessories describe the device response for each action or step record observations and inferences about design factors which potentially impact the user e list the effects of en
62. per which is used to show how a computer program will appear on a monitor Storyboard One page in a series of paper representations of the sequence of actions possible in a system Story boards representing a computer program could show keys prompts and changes in status Task The steps or work activities required of the user in order to perform functions Task analysis ldentification and analysis of the key user tasks and steps for a device The analysis may be conducted as a paper and pencil exercise for a device concept or by running through the procedures on a prototype or actual device Transfer of training The automatic application of skills habits or expectations to a new situation that appears similar to the one in which the skills and expectations were originally developed Usability Test A test of either an actual device or an advanced prototype with a fully functional user interface Data obtained includes user performance time errors and accuracy and subjective responses of test participants User performance data Information describing human behaviors and responses during task performance Examples of the criteria measured are frequency of accomplishing a task time required for task accomplishment and changes in performance with practice Ventilator A continuous ventilator respirator is a device intended to mechanically control or assist patient breathing by delivering a predetermined percentage of oxygen
63. plex issue because individuals differ in how they mentally integrate and conceptualize data that change over time Home use Lay people increasingly use medical devices Because of illness poor reading ability inadequate facilities insufficient assistance and inexperience this population often represents a special challenge to designers Decrements in vision hearing strength manual dexterity and memory are to be expected with age and illness Also many patients often are unfamiliar with automated devices and may be afraid to use them An additional concern is the potential effects of medications upon a patient s use of medical equipment For these reasons as well as lack of medical training the lay user s operation of highly complex devices is problematic Some devices that are difficult for physicians and nurses to operate find their way into the home where the problems are further compounded by power outages insufficient electrical outlets electromagnetic interference narrow doors the use of accessories e g batteries and other factors DESIGN IMPLICATIONS Obviously completely designing out all problems associated with human limitations environmental factors and stress is impossible Regardless the cumulative and interactive effects of user errors can be serious and even disastrous Designing the interface with the user in mind usually will result in a device that accommodates a wide range of users working under va
64. plugged battery light icon glows Battery and power lights are so small and If plugged in power light glows poorly positioned that the user probably will not notice power status Select Mode message appears for brief interval of 3 seconds User likely will miss mode indication and leave device in previous default mode Flow rate and volume displays show 0 even if there is a default value Many other pumps show default value from last use User may assume no default value with this pump see step 3 2 Press pump mode Mode light glows Mode lights do not blink are small and can button easily be missed Each is close to a key with no functional relationship Incorrect association is very possible 3 Press rate Flow rate displays default value from User experienced with another pump may button previous administration assume a 0 value by this point and miss default value see step 1 4 Enter flow rate As first value e g 100 ml is entered A distracted user not observing display values in device beeps and 100 is displayed User may intentionally or accidentally enter ml per hour can scroll in increments of 100 and more values without any auditory feedback successive values are displayed but no to indicate entry more beeps With constant pressure on key values may scroll up to 300 ml for example in 1 sec The research team visited a hospital after performing this analysis and by chance this
65. pump was used in the unit visited The head nurse stated that she had selected it because it seemed user friendly Unfortunately the unit staff found it so difficult to use that the head nurse now considers the pump not only an inconvenience to users but an impediment to safety and effectiveness If task analyses had been performed in the preceding example a set of guiding principles for pump setup might have emerged such as the following e Status indication and feedback should be precise and unambiguous Displayed alerts should be attention getting and in view until an action is taken Flow rate and volume entry mechanisms should be convenient for the user without sacrificing accuracy e g over scrolling Specific keys should operate in a consistent manner across modes 26 Do It By Design Hazard Analyses Human factors should be integrated into procedures used to isolate hazardous device failures Although these analyses conventionally deal with electrical and mechanical problems potential hazards associated with the user also should be evaluated One should assume that if errors can occur they will occur and that design may be a factor Hazard analysis meetings provided an excellent collection point for possible hazards uncovered from complaint files during earlier studies as well as from tests user studies and task analyses As a first step by considering errors as failures analysts can hypothesize what errors
66. rceptual physical and cognitive capabilities and limitations of individuals environmental interactions with human performance especially as mediated by user interface design human factors principles and methods generic problems associated with types of devices and Strengths and weakness of existing devices and the one under development Document reviews help one to ask the right questions avoid pitfalls and get the product design process off on the right track EXPLORATORY STUDIES Obtaining first hand information from physicians nurses and lay users is important in assessing the strengths and weaknesses of a device design Other potential participants to consider are risk managers clinical engineers maintenance personnel trainers and supervisors Questionnaires on duty observations interviews and focus groups are ways to assess design concepts mockups or predicate devices Why Do Such Studies Direct contact with the user population is essential for good human factors work It should be initiated in the earliest stages of product design Observations remarks 20 Do It By Design and anecdotal comments about existing devices desirable design features and working conditions can provide the following asnapshot of how healthcare professionals use devices a picture of how operating conditions including the multi device environment affect use asnapshot of what problems are encountered an
67. respond inappropriately if not given precise feedback and indications of functional status Do It By Design Product developers often incorporate multiple of functions into a device to provide flexibility and to serve a wider user community However extensive functional capability may well impose an unreasonable cognitive load on the user unless considerable effort is devoted to the design of the user interface The following are some problems that apply to many medical devices and can lead to errors Figure 2 Infusion Pump e illogical or cumbersome control sequences Flow rates Volume Dosage Status Indications Error Messages Etc unfamiliar language symbols or codes e inconsistencies among display formats e conventions that contradict user expectations uncertain or no feedback after input With current models users often must retrieve and remember large amounts e functions that are hidden from the user of information missing or ambiguous prompts symbols or icons unsignalled resets or defaults po status information missing lock outs or interlocks and requirements for complex mental calculations Examples of Errors Related to Software Design Many use errors induced by software design are incorrectly attributed to other factors because such errors are not easily remembered or recreated for post hoc analysis
68. riable often stressful conditions Do It By Design is less prone to user error and requires less user training In general human capability and limitations are extremely important considerations in device design The next section describes the kinds of user interface issues frequently encountered with medical devices Do It By Design THE USER INTERFACE This section describes and discusses problems related to human factors Hopefully the material will foster an appreciation of the impact of considering the user interface during design and provide the reader with the rationale and basic principles of human factors Brief summaries of serious incidents taken from the Food and Drug Administration s Medical Device Reporting MDR system illustrate the problems The summary principles found in the Rules of Thumb in each subsection are by no means exhaustive e g no detailed data on control dimensions and forces body dimensions audition vision or menu and screen design are included Consult guidelines textbooks articles and conference proceedings such as those listed in the References for Further Reading Finally design principles alone do not solve every user interface problem the human engineering process discussed later is vital to such solutions CONTROL DISPLAY ARRANGEMENT AND DESIGN Many devices have large consoles with rows of mechanical controls and displays The designer should consider the ability of users to
69. rototypes permit a great deal of flexibility in evaluating alternative designs prior to the final stages of development Developing Scenarios Written scenarios help provide the structure for what test participants actually will do A scenario generally is a written description of what the participants are expected 28 Do It By Design to accomplish and may be narrow or broad in focus depending upon the purpose of the test and the functionality of the prototype For example the participant might be asked to turn on an infusion pump and set it up for drug administration by keying in the appropriate flow rate and volume to be infused parameters A more advanced scenario might include other tasks such as installing the administration set performing primary and secondary infusion changing parameters and reacting to an emergency In all cases scenarios should be clearly written to help ensure consistency across participants and test conditions Healthcare professionals are of great use in creating scenarios and checking them for realism and accuracy Requirements and Measures User requirements are based primarily on earlier interviews observations manufacturer s experience analyses and literature reviews Some requirements are specific such as installation should take no more than 30 minutes At the conclusion of the test the actual performance times can be compared to these criteria In other instances initial requirements will be
70. sider the effects of ambient noise Ensure that the brightness of visual signals is sufficient to be perceived by users working under various conditions of ambient illumination Also brightness contrast and color contrast can help to optimize legibility Make labels and displays so that they can be easily read from typical viewing angles and distances Symbol size contrast color and display depth are important considerations Ensure that the abbreviations symbols text and acronyms placed on or displayed by the device are also used consistently in the instructional manual They also should correspond to standard nomenclature if possible Do It By Design Design control knobs and switches so that they correspond to the conventions of the user population as determined by user studies and existing medical device standards Arrange and design knobs switches and keys in a way that reduces the likelihood of inadvertent activation Use color and shape coding where appropriate to facilitate the rapid identification of controls and displays Colors and codes should not conflict with universal industry conventions e Space keys switches and control knobs sufficiently apart for easy manipulation This will also reduce the likelihood of inadvertent activation Make sure that controls provide tactile feedback Summary In summary the layout and design of controls and displays greatly affect the user s ability to suc
71. sly They are not intended as cookbooks The effectiveness of a guideline is in part determined by the education and skill of the person using it Understanding the rationale behind principles is important because the applicability of some principles may depend in part on the specific design in question as well as analytical research and test data Manuals Review of user instruction manuals may provide information about pitfalls to avoid and possible features to include when considering the development of a new product For example a warning such as be careful of automatic flow rate defaults may 19 Do It By Design indicate that such defaults are not clearly signaled or possibly may not be desirable in the first place The review and comparison of the written operating procedures and control panel illustrations may also point to a number of strengths or weaknesses in key layout operating logic and other user interface concerns during new product development Ideally once the user interface concept begins to take shape concurrent work on the instruction manual should begin Manual development should not be delayed until after the design effort is well under way or completed If manual development is coordinated closely with the design effort the very process of developing the new manual may uncover design problems Summary Review of the above types of documents can provide a clearer picture of the following sensory pe
72. ths occurred because users inserted a cassette from one infusion pump model into a different model for which the set was not compatible The resultant medication volumes were incorrect although pump operation and data display did not reflect this error 11 Do It By Design Numerous injuries deaths and near misses with ventilators have occurred because of disconnections of the breathing tubes due to poor tube and connector design The situation is exacerbated because many manufacturers sell a wide range of accessories for a given type of device There are a great variety of cables leads connectors valves and tubing on the market Accessories for different models are often similar in Figure 3 Connectors appearance and or difficult to install leading to misinstallations and disconnections Figure 3 illustrates the kinds of confusion that can lead to n ac installation errors However such accidents can A often be prevented through design solutions When conducting user studies tests and simulations it is crucial that device components and accessories be regarded as part of a system not isolated elements Improper connections are frequent causes of accidents Rules of Thumb The following are general considerations for reducing the likelihood of confusion between similar components and accessories and making improper connections Cables tubing connectors leuers and other hardware should be designed for
73. ugh problems with user interface do not negate one s responsibility for proper training and careful operation of a device poor design can greatly increase the 35 Do It By Design likelihood of errors Such errors can have serious consequences and cannot simply be trained away If there are serious flaws with the design of a device patterns may emerge Ask users about operational problems they have experienced with a given device Try to determine how widespread the problem is Biomedical engineers and other maintenance personnel constitute a valuable source of information In addition to individual interviews try a focus group or questionnaire approach Evaluating Already Purchased Devices Below are some indications of problems Observations Training has been slow and arduous Only a few staff members seem able to use the device Staff tends to modify the equipment or takes shortcuts Staff refuses to use the device Installation Problem e Staff finds installation of accessories difficult confusing or overly time consuming Alarms and batteries often fail Incorrect accessories sometimes are installed Parts often become detached Complaints Displays are difficult to read or understand Controls are poorly located or labeled Alarms are difficult to hear or distinguish 36 Do It By Design Device alarms are very annoying Device operation is illogical and confusing Incidents Acc
74. vironmental conditions and other devices on the user interface and performance and list the impact of the user interface on training requirements The following table shows a few steps from an analysis of a marketed infusion pump conducted by FDA The analysts were troubleshooting the user interface design In this example the human factors team found that performing the initial setup steps was quite easy but shortly into the exercise problems arose First the team had been operating on the assumption that the pump was plugged in when in fact it was not Because the battery and AC power icons were poorly located and very small they appeared as tiny dots at normal viewing distances and angles Therefore they were easily overlooked The team also discovered that users could miss important status information and prompts due to a very brief display of data When the keys for entering flow rates were depressed for more than a fraction of a second the values scrolled past the desired one In addition there was auditory feedback only after the initial key press not following each of the scrolled values Inconsistencies across operating modes in the operation of a double function key were found and these could be very confusing to the user 25 Do It By Design Sample of Task Analysis Steps from Analysis of an Actual Pump Troubleshooting the User Interface User Action Device Response Observed Problem 1 Push On button If un
75. vironments alarms sounding simultaneously or intermittently on one or more devices make proper identification difficult and staff may become distracted Alarms may be considered a nuisance or part of the background they also can induce stress Ambient noise and numerous visual displays can mask the output from a particular auditory or visual display overly loud alarms can mask other alarms Compounding the above problems are alarm failures and false alarms due to electro magnetic interference EMI static electricity or over sensitivity It is critical to test alarms in the environments in which they will be activated Problems and Examples Alarm problems include the following false alarms delayed alarms too sensitive or insensitive alarms alarms drowned out by noise ambiguous meanings inappropriate silencing and accidental disabling The two incidents below resulted from relatively common problems A patient receiving oxygen died when a concentrator pressure hose loosen ed The alarm was not loud enough to be heard over the drone of the device e A patient on a ventilator died following accidental detachment of the breathing tube from the humidifier The alarm did not sound because the pressure limit setting apparently was so low that it was essentially non functional Variations of these scenarios are common Low alarm intensity high ambient noise low battery conditions inappropriate alarm settings and other factors comb
76. ware 0 8 Examples of errors related to software design 0 000 eee eee 9 Rules OF WUMD s oae dee m eoe pokRUU RR ES TIN ES hanes CP RESI EU EE E 10 SUITS AUCRRPRRETICICTIDPCCDT TP 11 n 14 Problems and examples 54 2 cases XCR nO E ROIG RUE REG do OREL D cio VR 11 Rules of thumb oes ou ex oec pa ehh eed ERE Ron adem dete rex Rome ds eee tend 12 SUNIMONY uesda ku er ges Iicc X4 G3 x RR RES NEECK exe REN Rcs teks 13 13 Problems and examples 0000 cece eee teeta 13 Rules OF NUM 200406 pheGhectetees Seba inke rE e EAO EE saad she 13 Do It By Design Other Important Issues 0 0 0 0 000 ee ee eee eee 14 Dimensions forces and angles 2020 e cece eens 14 Transier of WAMNING esc or woke 001 70157 70 12127727 1T E 15 Device maintainability 0 0 0 0 cc eee 15 Device packaging auexeesvecersvedaiveeusaree lee een ees er e ri acid 16 SUMMAN MEET me ccs ee nese eee see tee EE TITIO 16 17 A E A deer ate 18 The Literature cc pure Pewee Re eee owen ewe cea we de hae waa D 18 Complaints and Recall Data 0 0 00 es 19 SII sssi sinh Ske Cees Oe SN eee COE Dede Ee ER ha eee ex 19 Manuals M r ccer mm 19 SUMMON ao cie x rau RE a cues 6 duet ed Nue Rus eain aes E od qos Eu fe d dos 20 Deeg ne ate e eee ogee a teens 20 Why Do Such Studies ues uq RR Pipes eo diced G3 cake ee bias eee 20 Study M
77. wledge of the user population is necessary Finally software designers need to coordinate their efforts closely with hardware designers COMPONENT INSTALLATION Among the most common errors reported to FDA are improper installations of device accessories Although erroneous installation often is not obvious before an accident design related installation problems frequently can be detected upon examination following an accident Proper installation is critical to safe device operation Problems and Examples Some commonly reported errors are tubing connected to the wrong port loose connections accidental disconnections electrical leads inserted into an improper power source batteries or bulbs inserted incorrectly and valves or other hardware installed backward or upside down The following MDR reports are illustrative Acomponent of an oxygen machine was installed upside down resulting in a patient death because of impeded air flow A ventilator was recalled after a low pressure alarm had short circuited on several occasions The failures were traced to misinstalled batteries resulting from design of the battery ports Three deaths were reported due to the introduction of a feeding solution from an enteral feeding tube into an IV tubing used for medication This happened because an adaptor intended to introduce medication from an IV tube into the enteral feeding system permitted the reverse operation Several injuries and dea

An Introduction to Human Factors in Medical Devices

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