VENTRICULAR ARRHYTHMOGENIC DOSE OF ADRENALINE DURING SEVOFLURANE, ISOFLURANE, AND HALOTHANE ANESTHESIA EITHER WITH OR WITHOUT KETAMINE OR THIOPENTONE IN CATS

The doses of adrenaline required to induce ventricular arrhythmia duri ng sevoflurane, isoflurane and halothane anaesthesia, either with or w ithout infusions of ketamine (76 mu g kg(-1) min(-1)) or thiopentone ( 0.5 mg kg(-1) min(-1)), were determined in cats. Groups of six to eigh t cats were maintained at end-tidal concentrations equivalent to 1.25 times the minimal alveolar concentration of each anaesthetic. The mean dose of adrenaline required to induce arrhythmia during sevoflurane a naesthesia (19.0 mu g kg(-1)) was approximately 11 times higher than t hat required during halothane anaesthesia (1.66 mu g kg(-1)) and the s ame as that required during isoflurane anaesthesia (19.0 mu g kg(-1)). Ketamine tended to decrease the requirement of adrenaline during halo thane anaesthesia, but not significantly, and did not change the requi rement during isoflurane or sevoflurane anaesthesia. Thiopentone did n ot change the requirement for adrenaline during halothane, isoflurane or sevoflurane anaesthesia. It was concluded that either with or witho ut ketamine or thiopentone, the effect of sevoflurane on the sensitisa tion of the feline myocardium to the arrhythmogenic effects of adrenal ine was significantly less than that of halothane and not different fr om that of isoflurane.