Effect of mild hypothermia on brain dialysate lactate after fluid percussion brain injury in rodents

OBJECTIVE: To investigate the effects of mild hypothermia on brain microdialysate lactate after fluid percussion traumatic brain injury (TBI) in rats. METHODS: Brain dialysate lactate before and after fluid percussion brain injury (2.1 +/- 0.2 atm) was measured in rats with preinjury mild hypothermia (32degreesC), postinjury mild hypothermia (32degreesC), injury normothermia (37degrees), and the sham control group. Mild hypothermia (32degreesC) was induced by partial immersion in a water bath (0degreesC) under general anesthesia and maintained for 2 hours. RESULTS: In the normothermia TBI group, brain extracellular fluid lactate increased from 0.311 +/- 0.03 to 1.275 +/- 0.08 mmol/L within 30 minutes after TBI (P < 0.01) and remained at a high level (0.546 +/- 0.05 mmol/L) (P < 0.01) at 2 hours after injury. In the postinjury mild hypothermic group, brain extracellular fluid lactate increased from 0.303 +/- 0.03 to 0.875 +/- 0.05 mmol/L at 15 minutes after TBI (P < 0.01) and then gradually decreased to 0.316 +/- 0.04 mmol/L at 2 hours after TBI (P > 0.05). In the preinjury mild hypothermic group, brain extracellular fluid lactate remained at normal levels after injury (P > 0.05). CONCLUSION: The cerebral extracellular fluid lactate level increases significantly after fluid percussion brain injury. Preinjury mild hypothermia completely inhibits the cerebral lactate accumulation, and early postinjury mild hypothermia significantly blunts the increase of cerebral lactate level after fluid percussion injury.