Abstract
We studied brain temperature and the effect of mild hypothermia in 58 patients after severe head injury (SHI). Brain tissue oxygen tension (p
ti
O
2
), carbon dioxide tension (p
ti
CO
2
), tissuie pH (pH
ti
) and temperature (T
br
) were measured using a multiparameter probe. Microdialysis was performed to measure glucose, lactate, glutamate, and aspartate in the extracellular fluid. Mild hypothermia (34° - 36°C) was employed in 33 selected patients who had persistent increased intracranial pressure (ICP > 20 mmHg). Mild induced hypothermia decreased brain oxygen significantly from 33 ± 24 mmHg to 30 ± 22 mmHg (p < 0.05). The p
ti
CO
2
(46 ± 8 mmHg) was also significantly lower during mild hypothermia (40.4 ± 4.0 mmHg), p < 0.0001). The pH
i
increased from 7.13 ± 0.15 to 7.24 ± 0.10 (p < 0.0001) under hypothermic conditions. Induced hypothermia may protect patients from secondary ischemic events by lowering the critical p
ti
O
2
threshold, reducing anaerobic metabolism, and decreasing the release of excitatory aminoacids. However, patients with spontaneous brain hypothermia on admission (T
br
< 36.0°C) showed significantly higher levels of glutamate as well as lactate, compared to all other patients, and had a worse outcome. Spontaneous brain hypothermia carries a poor prognosis, and was characterized by markedly abnormal brain metabolic indices. [Neurol Res 2002; 24: 161-168]
