BNF for Children 2011-2012

BNFC 2011–2012 15.1.2 Inhalational anaesthetics 633gas. To prevent hypoxia, the inspired gas mixture shouldcontain a minimum of 25% oxygen at all times. Higherconcentrations of oxygen (greater than 30%) are usuallyrequired during inhalational anaesthesia with nitrousoxide, see Nitrous Oxide, p. 634.Anaesthesia and skilled tasks See section 15.1.Volatile liquid anaestheticsVolatile liquid anaesthetics can be used for inductionand maintenance of anaesthesia, and following inductionwith an intravenous anaesthetic (section 15.1.1).Volatile liquid anaesthetics can trigger malignant hyperthermia(section 15.1.8) and are contra-indicated inthose susceptible to malignant hyperthermia. Theycan increase cerebrospinal pressure and should beused with caution in those with raised intracranialpressure. They can also cause hepatotoxicity in thosewho are sensitised to halogenated anaesthetics; halothanehas been associated with severe hepatotoxicity(important: see below). In children with neuromusculardisease, inhalational anaesthetics are very rarely associatedwith hyperkalaemia, resulting in cardiac arrhythmiasand death. Cardiorespiratory depression, hypotension,and arrhythmias are common side-effects ofvolatile liquid anaesthetics.Isoflurane is a volatile liquid anaesthetic. Heart rhythmis generally stable during isoflurane anaesthesia, butheart-rate can rise. Systemic arterial pressure and cardiacoutput can fall, owing to a decrease in systemicvascular resistance. Muscle relaxation occurs and theeffects of muscle relaxant drugs are potentiated. Isofluranecan irritate mucous membranes, causing cough,breath-holding, and laryngospasm. Isoflurane is thepreferred inhalational anaesthetic for use in obstetrics.Desflurane is a rapid-acting volatile liquid anaesthetic;it is reported to have about one-fifth the potency ofisoflurane. Emergence and recovery from anaesthesiaare particularly rapid because of its low solubility. Desfluraneis not recommended for induction of anaesthesiaas it is irritant to the upper respiratory tract;cough, breath-holding, apnoea, laryngospasm, andincreased secretions can occur.Sevoflurane is a rapid-acting volatile liquid anaestheticand is more potent than desflurane. Emergence andrecovery are particularly rapid but slower than desflurane.Sevoflurane is non-irritant and is therefore used forinhalational induction of anaesthesia. Sevoflurane caninteract with carbon dioxide absorbents to form compoundA, a potentially nephrotoxic vinyl ether. However,in spite of extensive use, no cases of sevofluraneinducedpermanent renal injury have been reported andthe carbon dioxide absorbents used in the UK producevery low concentrations of compound A, even in lowflowanaesthetic systems.Halothane is a volatile liquid anaesthetic that has largelybeen superseded by newer agents, but is usedoccasionally by very specialised paediatric anaesthetiststo manage difficult airways (with careful monitoring forcardiorespiratory depression and arrhythmias). Itsadvantages are that it is potent, induction is smooth,and the vapour is non-irritant and seldom inducescoughing or breath-holding.Halothane hepatotoxicitySevere hepatotoxicity can follow halothane anaesthesia.It occurs more frequently after repeatedexposure to halothane and has a high mortality.The risk of severe hepatotoxicity appears to beincreased by repeated exposures within a shorttime interval, but even after a long interval (sometimesof several years), susceptible patients havebeen reported to develop jaundice. Since there isno reliable way of identifying patients at risk, thefollowing precautions are recommended before theuse of halothane:. a careful anaesthetic history should be taken todetermine previous exposure and previous reactionsto halothane;. repeated exposure to halothane within a periodof at least 3 months should be avoided unlessthere are overriding clinical circumstances;. a history of unexplained jaundice or pyrexia in apatient following exposure to halothane is anabsolute contra-indication to its future use inthat patient.DESFLURANECautions see notes above; interactions: Appendix 1(anaesthetics, general)Contra-indications see notes abovePregnancy may depress neonatal respiration if usedduring deliveryBreast-feeding breast-feeding can be resumed assoon as mother has recovered sufficiently fromanaesthesiaSide-effects see notes aboveIndication and doseInduction of anaesthesia. By inhalation through specifically calibratedvaporiserChild 12–18 years 4–11%, but not recommended(see notes above)Maintenance of anaesthesia. By inhalation through specifically calibratedvaporiserNeonate 2–6% in nitrous oxide-oxygen; 2.5–8.5%in oxygen or oxygen-enriched airChild 1 month–18 years 2–6% in nitrous oxideoxygen;2.5–8.5% in oxygen or oxygen-enrichedairHALOTHANECautions see notes above (important: see HalothaneHepatoxicity above); avoid for dental procedures inthose under 18 years unless treated in hospital (highrisk of arrhythmia); avoid in acute porphyria (section9.8.2); interactions: Appendix 1 (anaesthetics, general)Contra-indications see notes aboveHepatic impairment avoid if history of unexplainedpyrexia or jaundice following previous exposure tohalothanePregnancy may depress neonatal respiration if usedduring delivery15 Anaesthesia