A Pressor Effect of Noncardioselective Beta Blockers in Mildly Hypertensive Patients During Surgery Under Anesthesia

Abstract

Sixty-two patients with mild hypertension were randomly assigned to receive no treatment, or 160 mg propranolol, or 200 mg metoprolol daily starting one week before elective surgery under anesthesia. The last dose was given two hours before anesthesia. Anesthesia consisted of induction with midazolam (2.5-5 mg) followed by thiopental (250-500 mg) and was maintained with 60% inspired N₂O in oxygen and 0.4% enflurane inspired. Airway carbon dioxide was monitored continuously by a CO₂ analyzer. Preoperative blood pressures were equally reduced by the two beta blockers. During anesthesia, however, blood pressure further decreased in the metoprolol group but not in the propranolol group.

The authors conclude that propranolol is less effective than metoprolol in mildly hypertensive patients during surgery under anesthesia, owing probably to a pressor response from propranolol during the stress of surgery. They also conclude, however, that the amount of blood pressure reduction by cardioselec tive beta blockade (metoprolol) may not be needed and that anesthesia itself is an effective means of reducing the blood pressure.