EFFECT OF PROPRANOLOL ON ARTERIAL HYPOTENSION INDUCED BY HALOTHANE IN THE DOG UNDER NITROUS OXIDE ANAESTHESIA

The effect of propranolol hydrochloride on arterial hypotensionproduced by halothane has been investigated in atropinized dogsduring nitrous oxide-oxygen anaesthesia. Propranolol alone produceda slight transient fall in blood pressure, but greatly enhancedthe hypotensive action of halothane. Following the applicationof electric shock to the heart to terminate adrenaline-inducedventricular fibrillation during halothane-nitrous oxide anaesthesia,propranolol produced a profound fall in arterial pressure. Ashock-like state associated with marked bradycardia resulted.Therapy with adrenaline and mephentermine produced slow recovery,and the pressor response was not associated with any increasein heart rate. The outcome of pressor therapy was related tothe number of electric shocks applied to the heart. Two dogsin which electric shock was applied thrice failed to recoverin spite of vigorous pressor therapy. It is suggested that cautionshould be exercised when injecting propranolol during halothaneanaesthesia in humans. The use of this drug following the applicationof electric shock to the heart to terminate ventricular fibrillationmay be hazardous and should be avoided.