Epinephrine-aminophylline-induced arrhythmias after midazolam or thiopentone in halothane-anaesthetized dogs.

The purpose of this study was to evaluate epinephrine-aminophylline-induced arrhythmias during halothane anaesthesia after induction with thiopentone or midazolam. Ten mongrel dogs were studied during 1 MAC halothane and 50% N2O:O2 anaesthesia while maintaining constant acid-base status. The minimal arrhythmogenic infusion rate of epinephrine (MAIRE) and the corresponding plasma concentration of epinephrine (MAPC) required to produce ventricular arrhythmias before and after aminophylline were higher following induction of anaesthesia with midazolam than with thiopentone (P less than 0.05); the MAIREs decreased stepwise with aminophylline (P less than 0.05). The correlation coefficient between individual MAIREs and MAPCs was 0.93 (P less than 0.001). Epinephrine alone and in combination with aminophylline was less arrhythmogenic after induction with midazolam than with thiopentone.