The Effects of ??-Adrenoreceptor Blockade on Oxygen Consumption During Cardiopulmonary Bypass

Abstract

The effect of chronic beta-adrenoreceptor blockade (beta-blockade) on hemodynamics and oxygen consumption (VO2) during cardiopulmonary bypass (CPB) in mild hypothermia (34 degrees C) was studied in 34 patients. The study group included 17 patients who received beta-adrenergic blocking drugs for at least 1 mo prior to the study. Seventeen patients who did not receive beta-adrenergic blockers served as controls. Demographic data in the two groups were comparable. Prior to induction of anesthesia, the heart rate was slower in the beta-adrenergic blocker group as compared to the control group. During CPB, measurements were made at two pump flow rates: 2.4 L.min-1.m-2 and 3.0 L.min-1.m-2. Oxygen delivery was similar in the two groups (beta-adrenergic blocker vs control) but the oxygen consumption was significantly lower in the beta-adrenergic blocker group as compared to the control group at both flow rates (P = 0.009). Increasing the flow rate from 2.4 L.min-1.m-2 to 3.0 L.min-1.m-2 produced a similar increase (P = 0.0001) in oxygen consumption in both groups. Increasing flow rate increased mean arterial pressure (MAP) and central venous pressure (CVP) and decreased systemic vascular resistance index (SVRI) and reservoir volume similarly in both groups. Thus, compared to the control group, patients on chronic beta-adrenergic blocker medication have a lower VO2 during CPB.