Hypothermia is a major problem in patients who have sustained trauma. We reviewed the cases of 100 consecutive trauma patients transferred directly to the operating room (OR) from the Emergency Department (ED) in a Level I trauma center; 26 cases could not be evaluated. Forty-two patients (57%) became hypothermic at some time between injury and leaving the OR. Fifty-five patients (74%) had a temperature (T) recorded on arrival to the ED; but only 7 (12%) were hypothermic (34.7 degrees +/- 1.5 degrees C). In contrast, 34 patients (46%) arrived in the OR hypothermic (34.8 degrees +/- 0.9 degrees C) and 26 (76%) of these left the OR hypothermic (34.8 degrees +/- 0.9 degrees C). Eight additional patients (20%) arriving in the OR with a T greater than 35.9 degrees C left the OR hypothermic (35.1 degrees +/- 0.4 degrees C). The mean T loss in the ED was significantly greater than that lost in the OR (-0.8 degrees +/- 0.7 degrees C vs. 0.0 degrees +/- 0.6 degrees C; p less than 0.0001, ANOVA). Ninety-two percent of the patients lost temperature in the ED, while 43% of the patients gained temperature in the OR. Hypothermia was associated with lower Trauma Scores, and those patients who were severely hypothermic received more intravenous fluids. However, the impact of fluid infusion was not independent from Trauma Score and did not fully explain the magnitude of the heat loss. These data suggest that hypothermia in trauma patients has a multifactoral etiology related to the magnitude of injury and that the major T loss occurs in the ED rather than in the OR.(ABSTRACT TRUNCATED AT 250 WORDS)