Effects of Mild Hypothermia And Rewarming on Renal Injury Following Coronary Artery Bypass Surgery
Munir Boodhwani, Fraser D. Rubens, Denise Wozny, Howard J. Nathan; University of Ottawa Heart Institute, Ottawa, ON, Canada
Comment on this Abstract
Objective: Hypothermia has been proposed as a potential strategy for visceral organ protection during cardiopulmonary bypass. However, the effects of intraoperative temperature on postoperative renal function are not known. We report data from randomized studies conducted to evaluate the effects of mild hypothermia and rewarming in patients undergoing coronary surgery.
Methods: Patient undergoing non-emergent, isolated coronary artery bypass surgery were enrolled into two separate study protocols. In the first protocol, patients (n = 223) were all cooled to 32°C during CPB and then randomly assigned to rewarming to 37°C (RW-37°) or 34°C (RW-34°). In the second protocol, patients (n = 267) were randomized to sustained mild hypothermia at 34°C (S-34°) or normothermia (S-37°) during the entire operative period without any rewarming. Serum creatinine levels were measured preoperatively and on post-operative days (POD) 0, 1, 2, 4, and later if clinically indicated and creatinine clearance was calculated. Significant renal injury was defined as a 25% increase in serum creatinine (or a 25% decrease in creatinine clearance) in the postoperative period. Repeated measures analyses were employed.
Results: Post-operative serum creatinine levels were persistently higher in the patients rewarmed to 37°C (RW-37°) compared to their hypothermic counterparts (RW-34°, p < 0.01, Fig. 1). Rewarmed patients (RW-37°) also had a higher incidence of renal injury (17% vs. 9%, p = 0.07) compared to hypothermic patients (RW-34°). Sustained mild hypothermia had no beneficial effect on post-operative serum creatinine levels (p = 0.44, Fig. 1) or the incidence of significant renal injury (S-34° vs. S-37°, 20% vs. 15%, p = 0.28). Multivariate analysis identified diabetes (OR [95% CI] - 1.6 [1.3 - 2.1]), prolonged CPB time (1.1 [1.0 - 1.2]), and rewarming (1.4 [1.0 - 1.9]) as independent risk factors for significant renal injury. Renal injury was associated with longer hospital stay (8.4 ± 0.8 vs. 6.8 ± 04 days, p <0.001).
Conclusion: In these randomized trials of patients undergoing isolated coronary surgery, sustained mild hypothermia does not improve renal outcome. However, rewarming on cardiopulmonary bypass is associated with increased renal injury and should be avoided.
Baseline and post-operative serum creatinine levels
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