Intravenous labetalol versus sodium nitroprusside for treatment of hypertension postcoronary bypass surgery

Abstract

Hypertension is common following coronary artery bypass surgery. The safety of labetalol, a recently released combined α1- and β-adrenergic blocking agent for treatment of hypertension in this clinical situation is controversial. The authors compared the hemodynamic effects of labetalol with those of sodium nitroprusside (SNP) in 91 patients with good left ventricular function and equally severe coronary artery disease and in whom coronary artery bypass surgery had been just completed. They were anesthetized using fentanyl, diazepam, and enflurane. If hypertension developed postoperatively, patients were randomized to receive labetalol, 2 mg/min to a maximum of 300 mg (20 patients) or sodium nitroprusside in 0.5 μg·kg-1·min-1 increments by infusion (20 patients) to return blood pressure to normal. Compared with control values, labetalol brought about significant (P < 0.05) reductions in heart rate, and cardiac index. No change was noted in stroke volume or systemic vascular resistance, but slight increases were found in central venous pressure and pulmonary capillary wedge pressure. Sodium nitroprusside treatment caused significant increases in heart rate and cardiac index while reducing diastolic blood pressure, central venous pressure, and pulmonary capillary wedge pressure. Stroke volume remained unchanged. Follwing the study period, blood pressure was controlled in all patients with SNP. Total doses of SNP in the 16 h following the study period were significantly less in the labetalol group (46.6 ± 11.7 mg) versus (116.1 ± 10.3 mg) in the SNP group (P < 0.05). In this clinical circumstance, labetalol can be safe and effective for controlling hypertension, but its mechanism of achieving this effect varies from that for sodium nitroprusside. Labetalol may improve myocardial oxygen balance and allow for reduced cumulative doses of sodium nitroprusside in this clinical setting.