Etomidate by infusion for neuroanaesthesia. Kinetic and dynamic interactions with nitrous oxide

An etomidate infusion was used to anaesthetise twelve patients for spinal surgery; six (group I) with 67% nitrous oxide and six (group II) with oxygen enriched air. Anaesthesia was induced with infused etomidate at a rate of 100 micrograms/kg/minute for 10 minutes and maintained at a rate of 10 micrograms/kg/minute. Recovery was assessed as the time to opening eyes on command (t1) and the time to giving correct date of birth (t2). In group I, mean value for t1 was 37.9 minutes and t2 59.1 minutes which is significantly longer than in group II where mean value for t1 was 9.0 minutes and t2 15.1 minutes. Blood was taken for estimation of etomidate levels. In group I the maintenance level was 501 ng/ml and the plasma clearance 20.9 ml/kg/minute. In group II the maintenance level was 367 ng/ml and plasma clearance 27.3 ml/kg/minute. Etomidate infusion appears to be a suitable alternative for neuroanaesthesia when nitrous oxide is contra-indicated.