Effects of Mild Hypothermia and Alkalizing Agents on Brain Injuries in Rats with Acute Subdural Hematomas

Brain ischemia is the leading pathopysiological mechanism in the development of secondary brain damage after acute subdural hematoma (SDH). Hypothermia has been employed as an effective cerebroprotective treatment on brain injuries, but the control of the general condition is very difficult under hypothermia, and various severe complications have been reported. Cerebral acidosis in the ischemic area is one of the important factors augmenting the brain edema formation. Tris-(hydroxymethyl)-aminomethane (THAM) has been used as an alkalizing agent for acidosis on brain injury and is reported to be effective. In the present study, we used a rat acute SDH model to assess the effect of mild (35°C) hypothermia and THAM combined treatment on brain water content, brain ischemia, and blood-brain barrier (BBB) permeability at 4 h after hematoma induction. Mild hypothermia did not significantly reduce the brain water content beneath the hematoma (79.5 ± 0.2%) compared to normothermia (80.2 ± 0.2%), but mild hypothermia combined to THAM resulted in a significant reduction (78.7 ± 0.0%; p < 0.01). Combined with mild hypothermia, THAM treatment significantly reduced the Evan's blue extravasation(35 ± 7 ng/g wet tissue; p < 0.05) compared to normothermia (63 ± 7 ng/g wet tissue). Furthermore, the volume of infarction at 24 h after the hematoma induction (54 ± 3 mm³;p < 0.01) was significantly smaller by the combined treatment compared with normothermia (70 ± 2 mm³). The present findings indicate that mild hypothermia of 35°C combined with THAM presents a potent cerebroprotective strategy. The protection of the BBB is one of the possible cerebroprotective mechanisms in this rat acute SDH model.