Effect of chronic nifedipine therapy on the haemodynamic response to phenylephrine before and during halothane anaesthesia.

We evaluated the effect of chronic oral nifedipine therapy (30-80 mg day-1) on the haemodynamic response to the alpha 1-agonist phenylephrine (PE) in 10 patients before and during halothane anaesthesia. The response was compared to a control group of eight patients not taking any cardiovascular drugs. No patients had ganglionic, beta-adrenergic, or muscarinic pharmacological blockade as in prior studies in the literature, and thus had intact cardiovascular reflexes. In all patients, PE caused a dose-related increase in arterial pressure and fall in heart rate and cardiac index. The response in patients taking nifedipine was not significantly different from that measured in controls. One-per-cent halothane in oxygen did not alter the overall haemodynamic response to PE in either group.