Blood pressure after cardiopulmonary bypass: which technique is accurate?

To evaluate the accuracy with which a patient's aortic blood pressure can be estimated upon separating from cardiopulmonary bypass (CPB), simultaneously recorded radial artery pressure, oscillometric brachial artery pressure, pressure in the CPB circuit, and the surgeon's estimate of blood pressure by aortic palpation were compared to directly measured aortic root pressure. After obtaining institutional approval and written informed consent, 20 patients requiring CPB for cardiac operations were studied. General anesthesia was induced and maintained with fentanyl, vecuronium, and enflurane. Blood pressure measurements were made before CPB and repeated 2, 5, and 10 minutes after discontinuation of CPB. Radial artery systolic pressure before CPB and radial artery mean pressure 10 minutes after CPB were different from the aortic root pressures (P < 0.05). Although the other radial artery pressures and the surgeon's estimate of systolic aortic pressure were statistically similar to the aortic root pressures, the range of differences was clinically significant. The oscillometric technique and CPB line were poor estimates of aortic root pressure. Of the techniques used to estimate aortic blood pressure, including radial arterial, oscillometric, aortic line of the CPB circuit, and digital palpation, the radial arterial was the best, and the aortic line from the CPB machine and palpation by the surgeon were the worst. When a clinician is unsure of the blood pressure during separation from CPB, direct measurement of central aortic blood pressure is advised.