80<strong>Update</strong> <strong>in</strong> <strong>Anaesthesia</strong>What agents are available?The <strong>in</strong>halation agents that are commonly used <strong>in</strong> Africaand other places where resources are limited are etherand halothane. When it is available, trichloroethylene isalso used.In the West halothane has been displaced by newer agents:isoflurane and sevoflurane. (Halothane is still widely used<strong>in</strong> paediatric anaesthesia.) These are far more costly thanhalothane and will not be considered <strong>in</strong> detail, though ifyou get the chance to use isoflurane you will be impressedhow good the recovery is compared to halothane. Ether,of course, is never used <strong>in</strong> the western world andtrichloroethylene has a dim<strong>in</strong>ish<strong>in</strong>g number of users worldwideand is hard to get. Laboratory grade is still available.The <strong>in</strong>dividual agents that are used all over Africa andelsewhere will be described now <strong>in</strong> detail:ETHER (diethyl ether)This is a very cheap agent as it is non-halogenated, madefrom sugar cane via ethanol us<strong>in</strong>g recycled sulphuric acid.With suitable fire precautions, it could easily be made locally<strong>in</strong> any country with the will to be self-sufficient.W.T.G.Morton demonstrated its effects on a famousoccasion <strong>in</strong> Boston, USA, <strong>in</strong> 1846 and this event hasbecome recognised world-wide as the “first anaesthetic”.Physical properties: Low boil<strong>in</strong>g po<strong>in</strong>t: 35 deg C. HighSVP at 20 deg C : 425 mm Hg. Blood/Gas partitioncoefficient: 12 (high), MAC: 1.92% (low potency). Cost:from US$10/litre, accord<strong>in</strong>g to supplier. Ether is highlyvolatile and <strong>in</strong>flammable. In oxygen, it is explosive. It hasa very strong and characteristic smell.Advantages: stimulates respiration and cardiac output,ma<strong>in</strong>ta<strong>in</strong><strong>in</strong>g blood pressure and causes bronchodilatation,all due to its sympathomimetic effect mediated byTable 1Volatile agents and their physical properties.AGENT SVP <strong>in</strong> mmHg MAC Blood/Gas coefficient CommentsEther 425 1.92% 12 High volatilityLow potencyHigh solubilityTrichloroethylene 60 0.17% 9 Low volatilityHigh potencyHigh solubilityHalothane 243 0.75% 2.3 VolatileLow potencyLow solubilitySevoflurane 160 1.7 - 2% 0.6 VolatileLow potencyInsolubleIsoflurane 250 1.15% 1.4 VolatilePotentLow solubility
<strong>Update</strong> <strong>in</strong> <strong>Anaesthesia</strong> 81adrenal<strong>in</strong>e release. A good sole anaesthetic agent becauseof its analgesic effect. Does not relax the uterus likehalothane but gives good abdom<strong>in</strong>al relaxation. A safeagent.Disadvantages: flammable, slow onset, slow recovery,secretions +++ need<strong>in</strong>g atrop<strong>in</strong>e. Bronchial irritation, so<strong>in</strong>halation <strong>in</strong>duction of anaesthesia by mask is very difficultbecause of cough<strong>in</strong>g. PONV (postoperative nausea andvomit<strong>in</strong>g) is sometimes seen <strong>in</strong> Africa but is a majordisadvantage <strong>in</strong> the West, where patients vomit much more.Indications: Any general anaesthetic, but especially goodfor Caesarean section (because the baby tolerates it andthe uterus contracts well), and major cases with <strong>in</strong>tubation.It is life sav<strong>in</strong>g for poor risk cases us<strong>in</strong>g a low dose. Also<strong>in</strong>dicated when no supplementary oxygen is available.Contra-<strong>in</strong>dications: There are no absolute contra<strong>in</strong>dicationsfor ether.Scaveng<strong>in</strong>g should be carried out (where possible) to avoidcontact between heavy <strong>in</strong>flammable ether vapour anddiathermy apparatus or other electrical devices that mayspark and also to prevent exhaled vapour blow<strong>in</strong>g at thesurgeon.Practice po<strong>in</strong>ts: The best method is to give a highconcentration to a paralysed, <strong>in</strong>tubated patient. Thus afteratrop<strong>in</strong>e, thiopentone, suxamethonium and <strong>in</strong>tubation,generous IPPV is commenced with ether 15-20% andthen accord<strong>in</strong>g to the patient’s needs, the ether is reducedafter about 5 m<strong>in</strong>utes to 6-8%. Remember vaporiserperformance is variable. Poor risk, septic or shockedpatients may need only 2%. Switch off well before theend of the operation to avoid a prolonged recovery. Withskill you can have your patients almost awake as they moveoff the table. If you have a big strong man for a herniarepair, save yourself a lot of embarrassment and give hima sp<strong>in</strong>al <strong>in</strong>stead!It seems to be purely fortuitous, but the patients that benefitmost from ether anaesthesia, such as Caesarean sectionand emergency laparotomy (which comprise over 90%of all major surgery <strong>in</strong> Africa 2 ) do not need diathermy.Where diathermy is essential, eg. <strong>in</strong> paediatric surgery,halothane is a better drug, so the conflict between etherand diathermy rarely arises. At our hospital, we do notallow ether to be used with diathermy.HALOTHANE (“Fluothane”)Physical properties: Boils at 50 o C, SVP at 20 o C:243mmHg. Blood /Gas partition coefficient:2.3, MAC0.75%. Cost: US$ 140/litre.Advantages: Well tolerated, non-irritant, potent (lowMAC) agent, which is relatively <strong>in</strong>soluble <strong>in</strong> blood, giv<strong>in</strong>grapid <strong>in</strong>duction, low dose ma<strong>in</strong>tenance and rapid recovery.There is predictable, dose-related depression of therespiratory and cardiovascular systems. The ideal <strong>in</strong>halation<strong>in</strong>duction agent.Disadvantages: Perhaps too potent, and overdose iseasy. Poor analgesic properties necessitat<strong>in</strong>g deep planesof anaesthesia before surgery and especially <strong>in</strong>tubation canbe tolerated. No post-operative analgesia. Uter<strong>in</strong>erelaxation and haemorrhage at concentrations above 2%.Hypotension, dysrhythmias and especially dangerous withadrenal<strong>in</strong>e where cardiac arrest <strong>in</strong> VF readily occurs. Postoperativeshiver<strong>in</strong>g. “Halothane hepatitis” may very rarelyoccur (I have never seen a case <strong>in</strong> Africa). It is extensivelymetabolised <strong>in</strong> the body and is best avoided with<strong>in</strong> threemonths of a previous halothane anaesthetic unless the<strong>in</strong>dications to use halothane are considered to overridethe risk of this rare condition.Indications: almost all general anaesthesia, especiallypaediatrics. Inhalation <strong>in</strong>duction especially <strong>in</strong> upper airwayobstruction.Contra-<strong>in</strong>dications: simultaneous adm<strong>in</strong>istration withadrenal<strong>in</strong>e, especially dur<strong>in</strong>g spontaneous breath<strong>in</strong>g. Highdose for Caesarean section or uter<strong>in</strong>e evacuation. Historyof unexpla<strong>in</strong>ed hepatitis follow<strong>in</strong>g a previous anaesthetic.Dosage: Induction with 3%, reduc<strong>in</strong>g to 1.5% forma<strong>in</strong>tenance. Children need 2% for ma<strong>in</strong>tenance. Over4% for more than a few m<strong>in</strong>utes will produce an overdose.Practice Po<strong>in</strong>ts: Halothane alone is not ideal because ithas no analgesic properties. You need high concentrationsto abolish reflex activity, eg. stra<strong>in</strong><strong>in</strong>g on the endotrachealtube. This becomes expensive and may also be unsafe.The common cl<strong>in</strong>ical situation of an <strong>in</strong>tubated patientbreath<strong>in</strong>g spontaneously high concentrations of halothane<strong>in</strong> oxygen and air is potentially hazardous <strong>in</strong> the presenceof heart disease. Many anaesthetists get away with it <strong>in</strong>ignorance, but only because heart disease is uncommon<strong>in</strong> Africa.A common arrangement is to have two draw-overvaporisers <strong>in</strong> series conta<strong>in</strong><strong>in</strong>g halothane andtrichloroethylene. Where available, nitrous oxide iscommonly used for analgesia; opioids or regional blocksare alternatives.Supplementary oxygen is mandatory when us<strong>in</strong>g halothaneto avoid hypoxia.
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