Objective: To determine the predictors of core temperature on arrival in the intensive care unit (ICU) after cardiac surgery.

Design: Prospective, randomized trial.

Setting: Tertiary care medical center, operating rooms (ORs), and ICU.

Patients: 72 patients presenting for coronary artery bypass surgery.

Interventions: Randomized assignment for ambient OR temperature (16–18°C vs. 21–23°C) and rewarming endpoint on cardiopulmonary bypass (CPB; nasopharyngeal and urinary bladder temperatures ≥36.5°C and 34.0°C, respectively, vs. nasopharyngeal and urinary bladder temperatures ≥37.5°C and 36.0°C, respectively) at the time of separation from bypass.

Measurements and Main Results: The best (and only significant) predictor of core temperature on arrival in the ICU was rewarming endpoint at the time of separation from CPB (p = 0.004). Patient weight, height, body habitus, and nitroprusside administration did not significantly predict core temperature. Ambient temperature affected only body temperature when the duration of time in the OR after separation from bypass was prolonged (>90 min). A weighted average body temperature was a better predictor of complete rewarming than was any single monitoring site.

Conclusions: To reduce the incidence of hypothermia after cardiac surgery, the most important variable is rewarming endpoint achieved before separation from bypass. A warm ambient temperature (>21°C) may be beneficial if the duration of time in the OR after bypass is prolonged (>90 min).