Methods:

Background: Without active measures to counteract temperature loss, most patients become hypothermic during surgery, initially from redistribution of lower-temperature peripheral blood to core tissues after anesthetic induction, followed by anesthetic-induced widening of thermoregulatory thresholds in the cold operating room environment.

In the PROTECT study, patients ≥45 years of age planning to undergo major noncardiac surgery lasting 2-6 hours at 1 of 12 hospitals in China or at Cleveland Clinic were randomly assigned to a protocol of aggressive intraoperative warming to 37.0°C versus routine thermal management with a target of 35.5°C. Operating room temperature was maintained at 20°C, and temperature was measured in the nasopharynx or distal esophagus.

Patients in the aggressive warming protocol received: 1) prewarming with a forced air cover 30 minutes prior to anesthetic induction to mitigate redistribution-induced temperature loss, 2) application of two forced air covers during surgery as needed to maintain a target core temperature of 37.0°C, and 3) warming of all intravenous (IV) fluids to body temperature prior to administration. Patients in the routine thermal management arm received: 1) no prewarming prior to induction, 2) use of forced air warming during surgery only as needed to prevent core temperature from falling below 35.5°C, and 3) use of room temperature IV fluids.

The primary outcome was a composite of myocardial injury, nonfatal cardiac arrest, or all-cause mortality within 30 days. Secondary outcomes were deep surgical site infection within 30 days, red blood cell transfusion, duration of hospital stay, and hospital readmission within 30 days of surgery. Exploratory outcomes included reduction in hemoglobin on postoperative day 1, mean Quality of Recovery-15 score on postoperative day 3, 30-day superficial wound infection, and myocardial infarction according to the third universal definition.