The effect of hyperoxia during cardiopulmonary bypass on blood cell rheology and postoperative morbidity associated with cardiac surgery

Abstract

In a prospective randomized open study, 48 patients underwent coronary bypass operation using cardiopulmonary bypass (CPB), with the same type of membrane oxygenator. Twenty-four patients were oxygenated during CPB by high PO2 level between 190 and 300 mmHg (H-PO2) and in the remaining patients the PO2 was maintained low between 75 and 112 mmHg (L-PO2.) The groups were comparable regarding age, sex, perfusion time, aortic occlusion time and preoperative blood cell rheological status. The effect of possible oxygen toxicity was assessed by monitoring blood cell rheology and analyzing the postoperative complications. Blood cell rheology was studied using standard microfiltration methods and samples were taken regularly during CPB. There was a significant reduction in blood cell rheology in both groups during CPB in a time-dependent manner. The L-PO2 group had significantly better rheology than the H-PO2 group, which was first noted at 60 min for red cells (p<0.01). Following operation, the time spent on the respirator was significantly lower in the L-PO2 compared to the H-PO2 (5.3 h ± 1.8 h vs. 7.2 h ± 2.5 h, p<0.01). There was significantly more bleeding in the H-PO2 group (p<0.05) and the use of blood products was significantly raised (p<0.01). The total number of complications requiring treatment (arrhythmias, myocardial infarction, cardiovascular accidents and respiratory insufficiency) showed a significantly higher frequency in the H-PO2 (16/24 vs. 6/24; p<0.01) compared to the L-PO2. There were three cases of mild renal failure in the H-PO2 group which was managed with conservative treatment. A significantly higher liver enzymes (p<0.01) and creatinine levels (p<0.05) were seen in the H-PO2 group. This study suggests that the use of high PO2 levels during CPB might lead to increased morbidity postoperatively and should be avoided.