Inadequacy of nitrous oxide/oxygen mixtures for maintaining anaesthesia in cats: satisfactory alternatives.

Under carefully controlled conditions, nitrous oxide/oxygen mixtures alone, in concentrations up to 80% nitrous oxide, are shown to be unsuitable for maintaining anaesthesia during physiological recording in cats. An alternative technique is described, in which N2O/O2 (72.5% : 27.5%) is supplemented with minimal amounts of intravenous pentobarbitone (averaging 1 mg/kg/hr), following induction and surgical preparation under halothane. The technique is suitable for single unit recording from the CNS of cats in long-term acute experiments, especially those involving immobilisation with muscle relaxants. With appropriate antibiotic prophylaxis the technique is also suitable for shorter-term recording sessions in chronically implanted cats permitted to recover between sessions.