Objective: We studied the effect of hypothermia on intracranial pressure, systemic and intracranial hemodynamics, and metabolism in patients with severe traumatic brain injury to clarify the optimal temperature for hypothermia, with a view toward establishing the proper management techniques for such patients.
Methods: The study was performed in 31 patients with severe head injury (Glasgow Coma Scale score as high as 5). All patients were sedated, paralyzed, ventilated, and cooled to 33 degrees C. Brain temperature, core temperature, intracranial pressure, cerebral perfusion pressure, jugular venous oxygen saturation, mixed venous oxygen saturation, cardiac output, oxygen delivery, oxygen consumption, and resting energy expenditure were monitored continuously.
Results: Intracranial pressure decreased significantly at brain temperatures below 37 degrees C and decreased more sharply at temperatures 35 to 36 degrees C, but no differences were observed at temperatures below 35 degrees C. Cerebral perfusion pressure peaked at 35.0 to 35.9 degrees C and decreased with further decreases in temperature. Jugular venous oxygen saturation and mixed venous oxygen saturation remained in the normal range during hypothermia. Resting energy expenditure and cardiac output decreased progressively with hypothermia. Oxygen delivery and oxygen consumption decreased to abnormally low levels at rectal temperatures below 35 degrees C, and the correlation between them became less significant at less than 35 degrees C than that when temperatures were 35 degrees C or higher. Brain temperature was consistently higher than rectal temperature by 0.5 +/- 0.3 degrees C.
Conclusion: These results suggest that, after traumatic brain injury, decreasing body temperature to 35 to 35.5 degrees C can reduce intracranial hypertension while maintaining sufficient cerebral perfusion pressure without cardiac dysfunction or oxygen debt. Thus, 35 to 35.5 degrees C seems to be the optimal temperature at which to treat patients with severe traumatic brain injury.