DESFLURANE (I-653) AND SEVOFLURANE - HALOGENATED ANESTHETICS OF THE FUTURE

Sevoflurane is an halogenated methyl isopropyl ether. It is potent, non explosive and non flammable. It reacts with soda lime to form traces of a related ether which has not been shown to have any toxic effect on animals chronically exposed to it in a closed system. Induction of anaesthesia with sevoflurane is rapid and smooth, as predicted by a blood/gas partition coefficient of about 0.6 and an acceptable odour which allows the use of concentrations of up to 10 %. Its MAC has been reported to vary between 1.7 and 2.3 vol %. Sevoflurane causes dose-dependent cardiovascular and respiratory depression. Its effect on the cerebral circulation is similar to that of isoflurane. The extent of biotransformation is similar to that of enflurane, but its low solubility and rapid elimination confine this to the period of inhalation. No toxic effects on the kidneys, liver and haematopoietic system have been found. Desflurane is a fluorinated methyl ether, structurally very similar to isoflurane. It is non flammable and non explosive at clinical concentrations. It is more stable in the presence of soda lime than any of the volatile anaesthetic agents available. This agent must be delivered with a thermostated vaporizer within a closed circle system, as its boiling point is 23.5-degrees-C. Desflurane is less potent than isoflurane. Its MAC has been estimated to be about 7.2 vol % in man. Desflurane did not lead to any liver, lung or kidney injury in laboratory rats, even during hypoxia and enzyme induction. Desflurane undergoes little biotransformation, although the presence of volatile metabolites or covalent tissue-bound products cannot be excluded. It has a low blood/gas partition coefficient of about 0.4. Recovery from anaesthesia is faster than with all the other volatile anaesthetic agents, whatever the duration of anaesthesia or the inspired concentration. In animals, it has been shown that the cardiovascular effects of desflurane mimic those of isoflurane (peripheral vasodilatation, systemic hypotension, myocardial depression, coronary arterial dilatation). Desflurane has little effect on the arrhythmogenic threshold of catecholamines. It causes dose dependent respiratory depression. The central nervous system effects of desflurane are also similar to those of isoflurane.