Hypothermia and operative mortality during on-pump coronary artery bypass grafting

Abstract

Controversy surrounds the effect of hypothermia on operative mortality during cardiac surgery. The present study accessed a large clinical database of coronary artery bypass graft operations to address the issue. A retrospective review of the Society of Thoracic Surgeons Adult Cardiac Surgery Database identified patients treated with isolated, nonemergency, on-pump coronary artery bypass grafting from July 2011 to December 2012. The patients were divided into 3 groups according to their lowest core temperature during the procedure: moderate hypothermia (≤ 34 °C), mild hypothermia (>34 °C but ≤ 36 °C), and normothermia (>36 °C). The primary endpoint of the study was operative mortality, defined according to the Database criteria. During the study period, 142,541 patients were available for analysis; 94,777 (66.5%) received moderate hypothermia, 42,750 (30.3%) mild hypothermia, and 5014 (3.5%) normothermia. Operative mortality occurred in 1394 patients (1.5%) in the moderate hypothermia, 534 (1.3%) in the mild hypothermia, and 105 (2.1%) in the normothermia group. Multivariate analysis identified hypothermia (both mild [odds ratio, 0.66; 95% confidence interval, 0.54-0.81; P < .0001] and moderate [odds ratio, 0.73; 95% confidence interval, 0.60-0.89; P = .0015]) was protective against operative mortality compared with normothermia. No incremental benefit was noted between the different hypothermia grades (P = .0827). Most patients receive hypothermia during on-pump coronary artery bypass grafting. Hypothermia is protective against operative mortality compared with normothermia in such patients. Moderate hypothermia does not provide additional survival benefit.