Bronchospasm and hypotension during cardiopulmonary bypass after preoperative cimetidine and labetalol therapy

A 64-yr-old asthmatic patient underwent a two-vessel aortocoronary vein grafting. Before surgery, the patient received cimetidine 400 mg and labetalol 650 mg. During the first 60 min of bypass, hypotension (40-45 mm Hg) was observed in spite of phenylephrine 14 mg. This initial hypotension was followed, during rewarming, by a slow increase in arterial pressure to 150 mm Hg. On cessation of bypass, bronchospasm was observed and was protracted. It is assumed that labetalol clearance and metabolism were reduced by cimetidine, that labetalol alpha-antagonism was responsible for the vasodilatation withstanding the phenylephrine, and that a combination of labetalol beta-antagonism and phenylephrine alpha-agonism initiated the bronchospasm. These observations indicate that, after labetalol therapy, higher doses of vasopressor agents such as phenylephrine may be necessary, but that such therapy may lead to bronchospasm in asthmatic patients.