Cerebral hypoperfusion in immediate postoperative period following coronary artery bypass grafting, heart valve, and abdominal aortic surgery

Abstract

Perioperative levels of jugular bulb oxyhaemoglobin saturation (SjO2) and lactate concentration (Lj), and postoperative duration of SjO2<50% were compared between patients undergoing coronary artery bypass grafting (CABG) (n=86), heart valve (n=14) and abdominal aortic (n=16) surgery. Radial artery and jugular bulb blood samples were aspirated after induction of anaesthesia, during re-warming on cardiopulmonary bypass (CPB) (36°C), on arrival in the intensive care unit (ICU) and, subsequently, at 1, 2 and 6 h after ICU admission. Most patients having heart surgery were hypocapnic at 36°C on CPB. Following CABG and heart valve surgery, many patients were hypocapnic whereas after abdominal aortic surgery, most were hypercapnic. During CPB and postoperatively, SjO2 and Lj were significantly correlated to PaCO2 and the arterial concentration of lactate (La) respectively (P<0.05). After correction for arterial carbon dioxide tension (PaCO2) and La, there were no significant changes in SjO2 or Lj on CPB. Postoperatively, having corrected for PaCO2, there were significant effects on SjO2 over all groups as a result of time from surgery (P<0.001) and its interaction with operation type (P<0.001). Following correction for La, there were no postoperative effects on Lj. No significant differences (P=0.2) in duration of SjO2<50% existed between patients undergoing CABG (1054 (82) min), abdominal aortic (893 (113) min) and heart valve (1073 (91) min) surgery. The lack of significant reciprocal effects on Lj combined with the frequency of hypocapnia and strong influence of PaCO2 on SjO2, suggest that SjO2 <50% during CPB and after cardiac surgery represents hypoperfusion as a consequence of hypocapnia rather than cerebral ischaemia.