Effects of therapeutic hypothermia on intracranial pressure and outcome in patients with severe head injury

Objective: Therapeutic hypothermia may improve outcome in patients with severe head injury, but clinical studies have produced conflicting results. We hypothesised that the severe side effects of artificial cooling might have masked the positive effects in earlier studies, and we treated a large group of patients with severe head injury with hypothermia using a strict protocol to prevent the occurrence of cooling-induced side effects. Design: Prospective clinical trial. Setting: University teaching hospital. Patients: Hundred thirty-six consecutive patients admitted to our hospital with severe head injury (Glasgow Coma Scale (GCS) less than or equal to8). Measurements and results: Patients included are the 136 patients with a GCS of 8 or less on admission in whom intracranial pressure (ICP) remained above 20 mmHg in spite of therapy according to a step-up protocol. Those who responded to the last step of our protocol (barbiturate coma) constituted the control group (n=72). Those who did not respond to barbiturate coma (n=64) were treated with moderate hypothermia (32-34degreesC). Average APACHE II scores were higher (28.9 +/- 44.4 vs 25.2 +/- 12.1, p<0.01) and average GCS at admission slightly lower (5.37 +/- 1.8 vs 5.9 +/- 2.1, p<0.05) in the hypothermia group, indicating greater severity of illness and more severe neurological injury. Predicted mortality was 86% for the hypothermia group versus 80% in controls (p<0.01). Actual mortality rates were significantly lower: 62% versus 72%; the difference in mortality between hypothermic patients and controls was significant (p<0.05). The number of patients with good neurological outcome was also higher in the hypothermia group: 15.7% versus 9.7% for hypothermic patients versus controls, respectively (p<0.02). These differences were explained almost entirely by the subgroup of patients with GCS of 5 or 6 at admission (mortality 52% vs 76%, p<0.01; good neurological outcome 29% vs 8%, p<0.01). Conclusions: Artificial cooling can significantly improve survival and neurological outcome in patients with severe head injury when used in a protocol with great attention to the prevention of side effects. Because there is likely to have been bias against the hypothermia group in this study, the positive effects of hypothermia might even have been underestimated. In addition, our results confirm the value of therapeutic hypothermia in treating refractory intracranial hypertension.