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.
Boodhwani
Munir
M
Division of Cardiac Surgery, University of Ottawa Heart Institute, Ottawa, Ontario, Canada.
Rubens
Fraser D
FD
Wozny
Denise
D
Nathan
Howard J
HJ
D000368:Aged; D000704:Analysis of Variance; D002315:Cardiopulmonary Bypass / Q000379:methods; D016001:Confidence Intervals; D001026:Coronary Artery Bypass / Q000379:methods* / Q000401:mortality; D023921:Coronary Stenosis / Q000000981:diagnostic imaging / Q000401:mortality / Q000601:surgery*; D003404:Creatinine / Q000652:urine*; D017558:Elective Surgical Procedures / Q000379:methods; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007036:Hypothermia, Induced / Q000379:methods*; D007677:Kidney Function Tests; D007902:Length of Stay; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D011182:Postoperative Care; D011336:Probability; D011859:Radiography; D016032:Randomized Controlled Trials as Topic; D012016:Reference Values; D017694:Rewarming / Q000009:adverse effects / Q000379:methods*; D018570:Risk Assessment; D018709:Statistics, Nonparametric; D016019:Survival Analysis; D016896:Treatment Outcome
D003404:Creatinine