This review includes twenty-three randomised controlled trials involving 1614 patients with traumatic head injury. In each trial, the patients were randomly divided into two groups: one group remained at normal body temperature, and the other group was cooled to a maximum of 35 degrees Celsius (or 95 degrees Fahrenheit) for at least 12 consecutive hours. Cooling could be of the whole body (e.g. with a blanket with circulating cold water), or just the head (e.g. with a helmet with circulating cold water). Information on death, disability, and pneumonia were evaluated for each trial.
The review authors found that fewer people died or became severely disabled if they were treated with hypothermia, but this finding may be due to chance. It was also found that patients given hypothermia were more likely to develop pneumonia, and some patients died from pneumonia, but the increased risk of pneumonia could also be due to chance.
Some of the trials included in the review were of low methodological quality. Low quality trials have a tendency to overestimate the effect of a treatment. In this review, the lower quality trials showed hypothermia treatment to be somewhat effective in reducing death and disability among patients with head injury. However, the good quality trials showed no decrease in the likelihood of death with hypothermia treatment and a reduced likelihood of pneumonia. Some of the findings in this review are therefore contradictory, and this is probably due to the inclusion of data from low quality trials.
The review authors conclude that there is no evidence that hypothermia is beneficial in the treatment of head injury. Most of the positive and negative effects found may be due to chance. Hypothermia should not be used except in the context of a randomised controlled trial with good allocation concealment.