Effects of Mild Hypothermia and Rewarming on Renal Function After Coronary Artery Bypass Grafting

Background. Hypothermia is a potential strategy for visceral organ protection during cardiopulmonary bypass (CPB). We report data from two randomized studies evaluating mild hypothermia and rewarming on postoperative renal function in cardiac surgical patients. Methods. Patients undergoing nonemergency, isolated coronary artery bypass grafting were enrolled into two studies. In the first, 223 patients were cooled to 32 degrees C during CPB and randomly assigned to rewarming to 37 degrees C (RW-37 degrees) or 34 degrees C (RW-34 degrees). The second study randomized 267 patients to sustained mild hypothermia at 34 degrees C (S-34 degrees) or normothermia (S-37 degrees) without rewarming. Serum creatinine levels were measured. Creatinine clearance was calculated. Significant renal dysfunction was defined as a 25% increase in serum creatinine or a 25% decrease in creatinine clearance postoperatively. Results. Postoperative serum creatinine levels were persistently higher in the RW-37 degrees patients than in the RW-34 degrees group (p < 0.01). RW-37 degrees patients had a higher incidence of renal dysfunction (17%) than RW-34 degrees patients (9%, p = 0.07). Sustained mild hypothermia had no beneficial effect on postoperative serum creatinine levels (p = 0.44) or significant renal dysfunction: S-34 degrees, 20% vs S-37 degrees, 15% (p = 0.28). Diabetes (odds ratio [OR], 1.6; 95% confidence interval [CI] 1.3 to 2.1), prolonged CPB time (OR, 1.1; 95% CI, 1.0 to 1.2), and rewarming (OR, 1.4; 95% CI, 1.0 to 1.9) were independent risk factors for significant renal dysfunction. Renal dysfunction was associated with longer hospital stay (8.4 +/- 0.8 vs 6.8 +/- 04 days, p < 0.001). Conclusions. Sustained mild hypothermia does not improve renal outcome. However, rewarming on CPB is associated with increased renal injury and should be avoided.