Circulatory effects of pentazocine and pethidine during general anaesthesia with nitrous oxide, oxygen and halothane.

Pentazocine 30 mg and pethidine 30 mg were given intravenously to two groups of patients receiving general anaesthesia with nitrous oxide, oxygen and halothane. The injections were repeated after 10 minutes. The effects on cardiac output, arterial blood pressure, heart rate and central venous pressure were measured. Both drugs caused a transient fall (approximately 20 per cent) in cardiac output and a sustained rise in central venous pressure.