Oxygen delivery post-cardiopulmonary bypass may not be compromised by decreases in radial-aortic pressure gradients

Common hemodynamic changes following cardiopulmonary bypass (CPB) include decreases in the radial artery-to-aortic pressure gradient (R-A), decreases in systemic vascular resistance (SVR), and increases in cardiac index (CI). To help evaluate the clinical significance of a decreased R-A gradient, we compared oxygen delivery (DO2) pre- and post-CPB. As a pilot study, data were collected from 20 consecutive patients undergoing routine cardiac surgery. Radial and aortic pressures (R-A gradient), DO2, CI, and SVR were determined five minutes before and after CPB.Average systolic R-A gradients changed from positive pre-CPB (+13.85 mmHg) to negative post-CPB (-3.85) (p< 0.001). Mean pressure gradients showed the same reversal (p < 0.001). CI increased pre- to post-CPB, 2.14 liters min-1 m-2 to 3.02; p< 0.001. SVR decreased, 1342 dynes-sec-cm-5 to 827; p< 0.001. Average DO2 was unchanged (604.4 and 669.8 ml min-1). However, a subgroup of patients showed marked increases in DO2 despite decreases in R-A gradients.