Oxygen metabolism during and after cardiac surgery: role of CPB

Background Cardiopulmonary bypass (CPB) has been reported to increase oxygen metabolism and to influence the relation between oxygen consumption (V 2) and delivery (DO2) in the early hours after cardiac surgery. To investigate the role of CPB, we studied oxygen metabolism in coronary artery bypass procedures performed on-pump (CABG) and off-pump (OPCAB). Methods Twenty-five patients were randomized to undergo CABG (n = 14) or OPCAB (n = 11). All patients received the same anesthetic management. Oxygen metabolism variables were assessed before induction of anesthesia and up to 18-hours after surgery. Results At baseline, before induction of anesthesia, there were no differences between CABG and OPCAB in oxygen consumption (VO2), delivery (DO2), or extraction (ExO2). After surgery VO2 and ExO2 increased in both groups, while DO2 decreased. No significant differences between CABG and OPCAB were detected in postoperative VO2, DO2, and ExO2 levels. The relation between VO2 and DO2 was very similar in CABG and OPCAB patients throughout the study, and no significant differences were detected in slopes and intercepts of the regression lines between CABG and OPCAB at all time points. There was, however, a significant effect of time on the relation between VO2 and DO2: this relation was stronger in the postoperative period, and the slope of this relation increased over time as well. Conclusions A hypermetabolic state and progressive and significant increases in the strength of the relationship between VO2 and DO2 and in the slope of this relationship occur after both CABG and OPCAB. Cardiopulmonary bypass is not responsible for these changes in oxygen metabolism.