A comparison of radial, brachial, and aortic pressures after cardiopulmonary bypass

Abstract

Previous investigations have identified falsely low radial artery pressures after cardiopulmonary bypass (CPB). The present study investigates the relationship among radial, brachial, and aortic arterial pressures in 33 cardiac surgical patients following CPB. Two minutes after separation from CPB, clinically important (≥10 mmHg) underestimation of systolic aortic pressures occurred in 17 of 33 (52%) radial artery catheters, while occurring in seven of 33 (21%) brachial artery catheters. Radial artery mean pressure underestimated aortic mean pressure by ≥5 mmHg in 21 of 33 (61 %) patients two minutes after CPB, while an equivalent aortic-to-brachial artery mean arterial pressure difference occurred in nine of 33 (27%) patients. The incidence of aorticto-radial mean arterial pressure differences ≥5 mmHg decreased to 40% (four of ten patients) by ten minutes after CPB, although interpretation is complicated by decreased availability of aortic pressure measurements. Multivariate analysis failed to identify factors predisposed to central-to-peripheral pressure gradients. Radial and brachial arterial pressures were compared both before and after CPB in all 33 patients. Brachial artery systolic and mean pressures were higher than corresponding radial artery measurements two minutes after CPB ( P < 0.05), followed by gradual resumption of a normal brachial-to-radial pressure relationship over 60 minutes. Either vasospasm in the brachial and radial arteries or profound arteriolar vasodilation in the upper extremity might cause the observed central-to-peripheral arterial pressure differences. The progressive central-to-peripheral decrease in mean arterial pressure favors the latter mechanism. Since radial artery pressures reproduce aortic pressure unpredictably immediately after CPB, blood pressure should be measured more centrally (eg, ascending aorta or femoral artery) before initiating vasopressor therapy for hypotension upon separation from CPB. Brachial artery pressure underestimates post-CPB aortic pressure less frequently and less severely than radial artery pressure, but reproduction of aortic pressure was too inconsistent to warrant substitution of brachial artery catheters for radial artery catheters. Alternatives to radial artery pressures appear most advantageous for the first 20 minutes after CPB separation, but occasionally they facilitate accurate diagnosis of blood pressure abnormalities well beyond that period.