Draw-over Anaesthesia - Part 2 - E-safe
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1. be given using an ordinary intravenous drip and a watch with a second hand Prepare a solution of intravenous anaesthetic to a standard concentration e g ketamine 1000mg in a 500 ml bottle or bag of normal saline equal to ketamine 2mg ml You will need to know the number of drops ml of your giving set Prepare Update in Anaesthesia your apparatus give oxygen by facemask and induce anaesthesia with a fast running infusion you will need about 120mg of ketamine 60ml of the above dilution When the patient has lost consciousness give a muscle relaxant and intubate the trachea Reduce the infusion of ketamine to about 2mg min of the above dilution according to clinical signs for maintenance and give further doses of relaxant as necessary You must monitor your infusion continuously if it stops or becomes tissued the patient may become aware At the end of anaesthesia reverse the relaxant stop the ketamine make sure the patient is breathing well and put them in the recovery position Benzodiazepine premedication or postmedication will prevent dreaming and emergence reactions The addition of atropine will reduce excessive secretions You can use a similar technique with other intravenous agents but be warned that recovery after the use of barbiturate infusions may be very prolonged Oxygen Supplies We have already noted some of the problems of oxygen supplies in developing countries hospitals may have to purchase thei2. combination with other volatile anaesthetics If you plan an inhalational induction begin with halothane then change to ether once the patient becomes unconscious this is much quicker and more pleasant for the patient and you will see the contrast between the respiratory depression of halothane and the stimulation of ether Halothane has also been used successfully for military anaesthesia in combination with trich loroethylene using two Oxford Miniature Vaporisers in the Tri service apparatus The agents complement each other since halothane is a good hypnotic but a poor analgesic while the reverse is true of trichloroethylene Use 0 5 trichloro ethylene as a baseline and vary the concentration of halothane to obtain the required depth of anaesthesia Turn the trichloroethylene off a few minutes before the end of the operation as it takes a while to wear off Once again added oxygen is necessary Draw over Without Volatile Anaesthetics Whichever kind of general anaesthetic you use the patient must have a secure airway and adequate breathing There is no reason why you should not use the draw over system to provide these in conjunction with a total intravenous anaesthetic The invention of electronically controlled infusion pumps leads some to suggest that these may one day replace vaporisers for most anaesthetics but in many situations a carefully regulated and monitored intravenous infusion ofa drug suchas ketamine can
3. many simple procedures will prevent or correct breakdown The first rule is not to interfere with apparatus which is working well If you do have to make a repair obtain a copy of the service manual and make sure you have all the necessary spare parts and any special tools before you start Routine Care Like all machines your draw over system requires regular attention to keep it in good reliable working order One of the main advantages of draw over apparatus is that it is relatively simple to carry out these regular checks and simple repairs yourself but remember that vaporisers and valves are precision instruments and need to be handled carefully Never use excessive force Make sure your apparatus is stored in a clean dry place away from dusty environments Wipe it over regularly with a soft moist cloth and a little detergent Close off open ends with corks or plastic caps to prevent dust and insects getting inside Black anti static anaesthetic breathing hoses are liable to perish in humid atmospheres after use they will be wet inside from the water vapour in the patient s breath After use hang them vertically in a cupboard to allow them to dry Inspect them regularly looking especially for cracks in between the corrugations this is where they most often develop leaks If you do not use ether you do not need anti static hoses and white polythene corrugated hoses are both cheaper and moreresistant to humidity Che
4. source such as surgical diathermy a sparking electric socket or especially ina dry climate static electricity Flammable or explosive mixtures must therefore be separated from possible ignition sources there are two ways of doing this Separation in time Healthy patients are most likely to need added oxygen at the beginning of anaesthesia before and just after intubation and at its end before extubation At these times surgical diathermy is not inuse During the operation use ether air without added oxygen unless the patient is very sick old very young or anaemic or there are other indications such as pregnancy cardio respiratory disease or high altitude Separation in space During the use of flammable explosive mixtures no source of ignition is permitted in a zone of risk which extends 30 cm from all points of the breathing system where gas might escape thus no diathermy in the thoracic cavity head and neck or mouth is permitted but diathermy inthe bladder or abdominal cavity is considered safe A simple scavenging system a length of tubing to direct the expired gases away from the site of surgery is helpful In dry climates including air conditioning anti static precautions should also be used It is worth remembering that Western operating theatres are still mostly built with antistatic precautions since even without ether there is a risk of fires and explosions with other substances mixed with oxygen
5. vaporiser Cause metal fatigue after 5 10 years use Remedy order a replacement unit from the manufacturer This is very simple to exchange for the broken unit only a screwdriver needed to loosen 3 screws You will need Screwdriver replacement part 3 Broken window of the filler gauge Warning you must notuse an EMO witha broken filler gauge it will give a dangerously high concentration of ether Cause accidental breakage Remedy order and fit a replacement from the manufacturer Fitting is simple loosen 3 screws remove the old unit and slot in the replacement You will need screwdriver replacement part Problems with the Oxford Miniature Vaporiser OMV s used with halothane gradually become stiff to operate due to the build up of thymol used as a preservative in halothane in the mechanism To clean this off properly you will have to take the top offthe vaporiser First obtain the service manual you will almost certainly need to fit new rubber seals so order these at the same time A temporary repair can be achieved by pouring ether into the inlet and outlet ports and gently working the concentration control from side to side Do notuse excessive force Update in Anaesthesia or you will bend it The thymol will be dissolved by the ether Afterwards tip all the ether out and ventilate with the bellows to dry out the vaporiser before re filling it with the correct agent If you order a new OMV r
6. Update in Anaesthesia DRAW OVER ANAESTHESIA Part 2 Practical Application Dr M B Dobson Consultant Anaesthetist John Radcliffe Hospital Oxford OX3 9DU In the first article on draw over Georg Kamm described the apparatus used in draw over anaesthesia In this issue I want to describe the ways in which draw over apparatus can be used to provide safe high quality anaesthesia We must first recognise that safe anaesthesia is not produced by apparatus alone The essentials for safe anaesthesia in any situation include adequate pre operative assessment preparation and resuscitation of patients reliable intravenous access a pleasant and safe induction a secure airway adequate tissue oxygenation appropriate monitoring and rapid recovery None of these depends on high cost or high technology equipment but all require properly trained and reliable people on whom primary safety depends If you are responsible for anaesthesia in a district hospital and do not have extensive specialist training you are well advised to use a small number of safe widely applicable clinical techniques This will allow you to become thoroughly familiar and confident with them through regular practice No one can be safe or confident when they use an unfamiliar technique Restricting yourself to a small number of techniques also means that you use a limited number of drugs and it is easier to make sure that adequate stocks are held in the hospital which d
7. anometer li Flowmeter Figure 1
8. ck your inflating bellows or Ambu bag for cracks or perishing in the rubber These items are almost impossible to repair so it is wise to have a spare in the supply cupboard Regularly inspect your Ambu or other universal breathing valves and clean them when necessary The inlet and exhaust ports can be unscrewed by hand and the valve rubbers removed by gentle pulling Wash the inside and outside of the valve with warm soapy water and allow the parts to dry thoroughly before carefully re assembling the valve Most Ambu valves can be sterilised either with antiseptics or by autoclaving but sterilisation is only necessary if the valve has been contaminated by use on an infected patient for example one with tuberculosis When using the Oxford inflating bellows with an AMBU or other universal breathing valve ensure that you disable the flap valve nearest the patient using the magnet provided This will prevent the valves from jamming during intermittent positive pressure ventilation If your anaesthetic facemasks have an inflatable margin check the state of the rubber as it is likely to perish in time If the small bung used to retain the air is missing it should be replaced with a suitable substitute do not inflate the mask and tie a knot in the inflating tube Check your stock of endotracheal tubes regularly Red rubber tubes are liable to deteriorate in hot and humid conditions The inflatable cuff is especially vulnerabl
9. e and should be tested before use Special Attention for Vaporisers Drain and discard the contents of your vaporisers once a week to avoid the build up of deposits inside Vaporisers are precision instruments and must be treated with care When complicated repairs are needed the machine must be sent to a competent medical engineer or service centre but there are a number of simple problems which you can deal with yourself First of all write to the manufacturers to obtain a service manual and any replacement parts you will need When these have arrived set aside a time when the vaporiser will not be needed for clinical use and you have time to work on it Below are brief descriptions of some of the operations you should be able to manage on Penlon vaporisers EMO amp OMV the address is Penlon Ltd Radley Road Abingdon OX14 3PH Telephone 44 235 554222 Fax 44 235 555252 Other brands of draw over vaporisers generally need the attention of a service engineer The EMO Vaporiser Common Faults 1 The pointer sticks and is difficult or impossible to move Cause build up of sticky deposits around the internal rotor drum Remedy remove the drum and clean it re assemble the vaporiser You will need Maintenance manual screwdrivers artery forceps penetrating oil ether brass polish vaseline and possibly a new main gasket 2 The thermocompensator breaks only the metal disc is visible in the window on top of the
10. emember that there are many different models be sure to specify which you want The air inlet can be on the right usually for draw over or left for a compressed gas machine and the tapers can be either 22mm ISO draw over or 23mm cagemount compressed gas machine Make sure you know what you want before you order A video tape of the servicing of EMO and OMV vaporisers can be obtained from Dr Roger Eltringham Department of Anaesthetics Gloucestershire Royal Hospital Gloucester UK Technical Queries Dr Ray Towey from Tanzania writes to ask Q Isit possible to connect the outlet ofthe Puritan Bennett oxygen concentrator to an Oxford Miniature Vaporiser OMV to provide a continuous gas flow for an Ayres T piece paediatric breathing system My concern is that the outlet pressure of gas from the concentrator is too low to permit IPPV from an Ayre s T piece Short answer No problem but the flow from the concentrator of 4 litres minute means that with a fresh gas requirement of 150ml kg min you will be limited to using this system on patients under about 20kg if you exceed this rebreathing will be a problem Long answer There are actually 2 questions to answer Q1 Does the OMV work efficiently with a continuous gas flow of 4 litres min or less Answer The OMV works best in the intermittent flow of a draw over system but with continuous flows its performance at 4 litres min is satisfactory If the flow is red
11. enflurane trichloroethylene alcohol etc Using Other Volatile Anaesthetic Agents Halothane is widely available and has a number of advantages It is non flammable has a pleasant non irritant smell and induces unconsciousness more quickly than ether Its disadvantages are that it depresses the cardiovascular and respiratory systems resulting in hypotension and hypoxia It is more potent than ether and must never be given by open drop techniques Halothane should never be put in an EMO vaporiser as it attacks the metal from which these vaporisers are made and the vaporiser will be wrecked The most suitable draw over vaporiser for halothane is the Oxford Miniature Vaporiser which can also be used for other volatile anaesthetics if these are available e g trichloroethylene enflurane etc Halothane can be used alone for anaesthesia its main disadvantages in this situation is the respiratory depression which it causes and supplementary Update in Anaesthesia oxygen should always be used throughout the procedure If oxygen is not available ventilation should be assisted or controlled to prevent hypoxia Halothane sensitises the heart to adrenaline and you should warn the surgeon not to infiltrate the wound with adrenaline containing solutions when halothane is in use Some anaesthetists allow infiltration of up to 20 ml of 1 200 000 adrenaline provided the pulse is closely monitored Halothane may be very useful in
12. o not run out A draw over system is most suitable for the needs of district hospitals It is simple to understand robust independent of compressed gases and can be repaired on site if necessary In a draw over system the carrier gas air with or without oxygen enrichment passes through a low resistance vaporiser through a self inflating bag or bellows and reaches the patient via a universal breathing valve which ensures that expired gases are directed into the atmosphere and do not re enter the anaesthetic system Ether as an Anaesthetic Agent Ether has largely disappeared from anaesthetic practice in Western countries because of a number of apparent disadvantages it has a pungent smell and this combined with its high blood solubility prolongs the induction of anaesthesia with ether alone Ithas also been associated with post operative vomiting and people are concerned about possible dangers of fires and explosions Nevertheless ether has many important advantages it increases cardiac output and is a respiratory stimulant and is therefore the only volatile agent which can safely be used for spontaneously breathing patients if oxygen is not available It is certainly the safest volatile anaesthetic in the hands of the inexperienced or occasional anaesthetist and the experienced anaesthetist can easily use ether as part of amore sophisticated technique which avoids the problems of slow induction vomiting and delayed rec
13. overy Most of the disadvantages of ether are seen when it is used alone for induction ofanaesthesia They include aslow onset an unpleasant smell for the patient with coughing breath holding and laryngeal irritability salivation swallowing and sometimes vomiting In the vast majority of patients these problems can be easily and safely avoided by intravenous induction of anaesthesia with drugs such as thiopentone or ketamine Insertion of an endotracheal tube secures the airway and allows the concentration of ether to be increased rapidly to maintenance levels with no risk of laryngospasm If a muscle relaxant is used inhaled ether concentrations of 3 4 are enough to ensure unconsciousness and wake up reasonably rapidly at the end of surgery Ether also provides a considerably longer period of post operative analgesia than other volatile anaesthetics Thus the clinical disadvantages of ether can be overcome allowing us to make use of its advantages in safety availability and economy Asummary ofa suitable technique for ether anaesthesia is shown in Table 1 Page 20 The only problem remaining is the question of its flammability Ether is flammable will burn but not explode when mixed with air In this respect you can compare it with alcohol but not with petrol which will explode when ignited in air The addition of oxygen or nitrous oxide to ether does produce an explosive mixture in which ignition could be caused by a
14. r own cylinders and many of these go missing when sent for re filling With the draw over system missing cylinders do not cause the anaesthetic service to collapse but oxygen is still very desirable especially if your patient is very young old anaemic or ill The use of a T piece see Fig 1 to enrich a draw over system is very economical and allows you to make the most of your supplies A flow of 1 litre min provides an inspired concentration of 30 40 oxygen 4 litres min provides 60 80 To make the best use of oxygen post operatively or in cases of breathing difficulty due to respiratory infections etc use a nasopharyngeal catheter eg a 8 10FG rubber or plastic catheter inserted into the nasopharynx with a flow of 1 litre min for a child or 2 litres min for an adult giving an inspired concentration of about 40 oxygen It is desirable to humidify the flow of oxygen and vital to check that the catheter is not inserted too far e g into the oesophagus or gastric dilatation could result As well as its economy this method is preferred by many patients as it allows them to talk cough expectorate and eat all difficult to do with a conventional facemask Other sources of oxygen are worth considering Industrial welding oxygen is normally made by the same process as Medical oxygen and indeed industrial oxygen is often made to a higher degree of purity You must check your own local specification O
15. ss and preoxygenate the patient Give a sleep dose of thiopentone or ketamine Give 1mg kg suxamethonium i v Intubate the trachea Ventilate the lungs manually with 3 ether in air Increase this during the first 5 minutes to 6 10 to settle the patient Halothane 1 1 5 can be used instead of ether When breathing returns usually after 3 5 minutes allow the patient to breathe 6 8 ether in air or 1 1 5 halothane in oxygen enriched air or if available give a long term relaxant eg alcuronium or gallamine and continue to ventilate the lungs manually at an appropriate concentration of volatile agent This technique allows rapid recovery At the end of surgery reverse long acting muscle relaxants if given with neostigmine and atropine continuing to ventilate the lungs until breathing resumes turn the patient on his side and remove the tube when the patient is awake This universal technique can be used for almost all types of surgery and for both elective and emergency cases Update in Anaesthesia DRAW OVER ANAESTHESIA Part 3 Looking After Your Own Apparatus Dr M B Dobson Consultant Anaesthetist Oxford UK If you work in a district hospital it is unlikely that you will have the help of a skilled technician to look after your apparatus and the responsibility is therefore yours No apparatus will work reliably unless it is properly and regularly inspected and cared for Draw over apparatus is not difficult to understand and
16. uced to 2 litres min it will give significantly less than indicated I therefore recommend that you keep the flow at 4 l min for all sizes of patients up to 20kg Q2 Does the back pressure generated by IPPV with a T piece reduce the flow from the concentrator significantly Answer No Small concentrators like the Update in Anaesthesia Puritan Bennett and other WHO approved models Healthdyne amp DeVilbiss produce oxygen at a pressure of up to 5 p s i 0 35 bar 260 mmHg 340cm water The back pressure generated by IPPV is unlikely to exceed 30 cm water which is only a tenth of that available I have checked this in the laboratory using a P B concentrator and measuring the flow delivered through a high precision flowmeter while producing back pressure by applying a gate clamp to the oxygen tubing see figure 1 with the concentrator flow control set to deliver 4 l min Conclusions 1 Flow from the concentrator is well maintained 2 Even with significant back pressure the flow indicated onthe concentrator s flowmeter is areliable guide to the flow actually being delivered Concentrator until back pressure reaches 60 100 mmHg 75 130 cm Water Results are shown in Table 1 below The results obtained were as follows Table 1 Flow from Concentrator Back pressure Actual flow applied delivered 0 4 25 15 mmHg 30 mmHg 45 mmHg 60 mmHg 100 mmHg 200 mmHg 300 mmHg 500 mmHg D Nn M
17. xygen concentrators see Update No 1 can also provide a supply for draw over or ward use Concentrators compress room air to a pressure of 4 bar then pass it though a zeolite column which absorbs the nitrogen leaving up to 96 oxygen the rest is argon If excessive flows are demanded the concentration delivered falls off Small concentrators which meet the World Health Organisation s WHO standards can deliver 4 litres min of oxygen gt 90 witha power consumption of around 350 watts mains electricity or AC generator required Concentrators are usually the cheapest way of getting oxygen often 30 50 of the cost of cylinders They require simple servicing every 5000 hours and an overhaul every 20 000 equivalent in running time to about half a million miles for a car For details of WHO approved concentrators write to the author Low flow oxygen enrichment Room air A Open ended oxygen reservoir tube to Patient Vaporiser Figure 1 Adding oxygen to a drawover circuit Update in Anaesthesia Table 1 Suggested plan for General Anaesthesia Is General anaesthesia required for this case gt NO gt _ Useregional technique YES Is the anaesthetist trained in endotracheal gt NO gt Use ketamine or spinal intubation YES Has the patient a difficult airway gt YES Use regional or seek expert help lo Proceed as follows Check your apparatus and drugs Obtain intravenous acce
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