Summary

Induction of anaesthesia using the vital capacity rapid inhalation induction (VCRI1Two previous studies, in over 200 healthy volunteers, demonstrated the safety and acceptability of using the vital capacity rapid inhalation induction (VCRII) technique to induce anaesthesia with halothane and oxygen. 1,2 In 1986, Wilton and Thomas 3 modified the technique by using halothane in nitrous oxide and oxygen and confirmed, in 100 patients, the acceptability of the technique for rapid inhalation induction of anaesthesia.The VCRII technique has certain advantages over conventional inhalational or intravenous induction of anaesthesia, which include prompt induction without a prolonged excitatory phase, and full recovery without "hangover. '4 We assessed the use of the newly developed agent, sevoflurane, as an alternative to halothane for VCRII.

SummaryThis study compares vital capacity rapid inhalational induction of anaesthesia with sevofurane and isoflurane. Forty-six volunteers undergoing the procedure had one of the two agents: 2.5 had sevoflurane and 21 isc?purune. Subjects were unpremedicated and breathed approximately 1.7 MAC equivalents of either vapour. There were no signifcant diflerences in the patients' monitored cardiovascular, respiratory, and electrocardiographic variables. The mean time for induction of anaesthesia with sevojurane (I20 s) was significantly shorter than with isojurane (145 s), reflecting its higher blood-gas solubility. There were,fewer induction complications in the sevofurane group. Subjects in the sevopurane group found the induction of anaesthesia more pleasant and were more willing to undergo it again compared to subjects in the isoflurane group. We conclude that sevoflurane is superior to isofiurane in vital capacity rapid inhalational induction of anaesthesia, particularly in instances uvhere premedication should be avoided. Key wordsAnaesthetics volatile; isoflurane, sevoflurane. E.witator,v phase; induction.Ruffle and colleagues described the technique of vital capacity rapid inhalational induction (VCRII) in 200 patients [I], who were instructed to take a vital capacity breath of 4% halothane in oxygen, and to hold it in the lungs for 30-90s until loss of consciousness. The VCRII technique had certain advantages over conventional inhalation and intravenous induction of anaesthesia, including prompt induction without a prolonged excitatory phase and full recovery without 'hangover'. An editorial in Lancet acknowledged these advantages, but emphasised the potential for hepatic toxicity in repeated halothane anaesthesia [2].Two studies have described isoflurane as an alternative to halothane for VCRII [3,4]. They showed that isoflurane induced loss of consciousness more rapidly than halothane because of its lower blood-gas solubility and that isoflurane was well tolerated by patients. Sevoflurane, on the other hand, has an even lower blood-gas solubility than isoflurane [5], and could be expected to induce anaesthesia more rapidly. In this study, we compared sevoflurane and isoflurane for VCRII. MethodsThe study was approved by the Clinical Human Research Committee, and informed consent was obtained from each volunteer. Forty-six healthy volunteers were randomly divided into two groups. Twenty-five were assigned to the sevoflurane (S) group and 21 to the isoflurane (I) group, but they were unaware to which group they had been assigned. The groups were demographically similar with no significant differences between them in respect of age, sex, weight, or height. The S group breathed 3% sevoflurane in oxygen, and the I group 2% isoflurane in oxygen. These concentrations represented approximately I .7 MAC equivalents of each agent. None were premedicated.Mixtures of each anaesthetic agent together with oxygen were delivered by an Ohmeda Vapor vaporizer into the circle system of an Ohmeda anaesthesia machine. The insp...

A previous investigation using nitrous oxide with 5% enflurane (3.8 MAC) for single breath induction produced a stage of excitement which may be related to the difference in blood/gas coefficient solubility of these agents. The closer blood/gas solubility coefficient of sevoflurane and nitrous oxide may eliminate this phenomenon. We therefore evaluated 40 volunteers in a randomized study using 7.5% sevoflurane (3.7 MAC) in oxygen (n = 21) or sevoflurane with nitrous oxide (n = 19) using a single breath induction technique. Sevoflurane in nitrous oxide and oxygen reduced induction time by 15% compared to sevoflurane in oxygen alone (41 +/- 16 and 48 +/- 16 sec (s.d.), respectively). This was, however, not statistically significant. There were scarcely induction-related complications, such as coughing, laryngospasm, breath-holding, movements of a limb and excessive salivation, in either group. Thus, the addition of nitrous oxide neither increased the number of complications, nor the speed of induction.

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