Effect of mild hypothermia on partial pressure of oxygen in brain tissue and brain temperature in patients with severe head injury.

OBJECTIVE

To study the changes of partial pressure of oxygen in brain tissue (P(bt)O(2)) and brain temperature (BT) in patient s in acute phase of severe head injury, and to study the effect of mild hypothermia on P(bt)O(2) and BT.

METHODS

The P(bt)O(2) and the BT of 18 patients with severe head injury were monitored, and the patients were treated with mild hypothermia within 20 hours after injury. The rectal temperature (RT) of the patients was kept on 31.5-34.9 degrees C for 1-7 days (57.7 hours+/-28.4 hours averagely), simultaneously, the indexes of P(bt)O(2) and BT were monitored for 1-5 days (with an average of 54.8 hours+/-27.0 hours). According to Glasgow Outcome Scale (GOS), the prognosis of the patients was evaluated at 6 months after injury.

RESULTS

Within 24 hours after severe head injury, the P(bt)O(2) was significantly lower (9.6 mm Hg+/-6.8 mm Hg, 1 mm Hg=0.133 kPa) than the normal value (16-40 mm Hg). After treatment of mild hypothermia, the mean P(bt)O(2) increased to 28.7 mm Hg+/-8.8 mm Hg during the first 24 hours, and the P(bt)O(2) was still maintained within the range of normal value at 3 days after injury. The BT was higher than the RT in the patients in acute phase of severe head injury, and the difference between the BT and the RT significantly increased after treatment of mild hypothermia. Hyperventilation (the partial pressure of carbon dioxide in artery (P(a)CO(2)) approximately 25 mm Hg) decreased the high intracranial pressure (ICP) and significantly decreased the P(bt)O(2).

CONCLUSIONS

This study demonstrates that P(pt)O(2) and BT monitoring is a safe, reliable and sensitive diagnostic method to follow cerebral oxygenation. It might become an important tool in our treatment regime for patients in the acute phase of severe head injury requiring hypothermia and hyperventilation.