Mild hypothermia versus normothermia in patients undergoing cardiac surgery

Temperature during cardiopulmonary bypass (CPB) for cardiac surgery has been controversial. The aim of the current study is to compare the outcomes for patients with mild hypothermia versus normothermic CPB temperatures.

All patients who underwent cardiac surgery with CPB and temperatures ≥32°C from 2011 to 2018 were included, which consisted of mild hypothermia (32°C-35°C) and normothermia (>35°C) cohorts. Propensity matching (1:1) was performed for risk adjustment. Primary outcomes included operative and long-term survival. Secondary outcomes included postoperative complications.

A total of 6525 patients comprised 2 cohorts: mild hypothermia (32°C-35°C; n = 3148) versus normothermia (>35°C; n = 3377). Following adjustment for surgeon preference, there were 1601 propensity-matched patients who had similar baseline characteristics (standard mean difference, ≤0.10), including CPB time, crossclamp time, and intra-aortic balloon pump placement. Kaplan-Meier analysis showed no difference in long-term survival (82.6% vs 81.6%; P = .81). Over a median follow-up of 4.4 years, there were no differences in overall mortality (18.1% vs 18.1%; P = 1.1) or readmission (50.3% vs 48.3%; P = .2). Acute renal failure (3.7% vs 2.4%; P = .03) and intensive care unit hours (46.5 vs 45.1; P = .04) were significantly higher with hypothermia. There was no difference between cohorts for postoperative stroke (2.0% vs 2.0%; P = 1.0), reoperation (5.9% vs 6.0%; P = .9), or operative intra-aortic balloon pump placement (1.7% vs 1.8%; P = .9).

Patients with mild hypothermia during CPB had increased postoperative renal failure and length of intensive care unit stay. Although there was no difference in long-term survival, mild hypothermia does not appear to offer patients appreciable benefits, compared with normothermia.