Is hypothermia simply a marker of shock and injury severity or an independent risk factor for mortality in trauma patients? Analysis of a large national trauma registry

Background: Successful application of induced hypothermia (HT) after stroke and cardiac arrest has led to a resurgence of interest in its potential protective effects in trauma patients. Although clinical studies demonstrate an adverse effect, they consist of small studies from single institutions. We tested the hypothesis that HT is associated with improved survival in trauma patients by analyzing a large, national trauma database. Methods: The study included all patients in the National Trauma Data Bank (1994-2002) aged 18 to 55 years old with temperature at presentation to the emergency department and base deficit (BD) recorded. Hypothermic (temperature, <35 degrees C; n = 3267) patients and patients with normothermia (temperature, >= 35 degrees C; n = 35,283) patients were compared. Two analyses were conducted to control for the association between HT and injury severity. First, hypothermic and normothermic (NT) patients were stratified by injury severity score (ISS) and shock (blood pressure <= 90 mm Hg). Next, logistic regression was used to control for effects of age, sex, mechanism, ISS, head, chest, and abdominal injuries, BP, Glasgow Coma Scale score, and BD, with survival as the dependent and HT as the predictor variable. Results: Although HT was more common in more seriously injured patients, stratified analysis revealed that hypothermic patients have significantly higher mortality than patients with the same severity of injury who remain NT. Even after controlling for injury severity and the other potential confounders listed above, HT remained a strong, independent predictor of mortality (odds ratio, 1.19; 95% confidence interval, 1.05-1.35). Conclusion: There is no apparent protective effect of HT in trauma patients. HT itself, not just its association with shock, injury severity, and other cofactors lead to a significant increase in mortality in injured patients. Continued, aggressive efforts to prevent and treat HT are warranted.