Influence of rewarming conditions after hypothermia in gerbils with transient forebrain ischemia

Object. Recently, several studies have demonstrated that hypothermia has a beneficial effect on clinical outcome, however, it is difficult to determin e the appropriate rewarming conditions in clinical use. The pul pose of the present study was to examine the influence of rewarming conditions in gerb ils with transient forebrain ischemia. Methods. Ischemia was induced in the gerbils by a 5-minute bilateral common carotid artery occlusion, after which the animals were immediately subject ed to moderate or deep hypothermia. After moderate hypothermia (30.5 degree s C for 4 hours) the animals were rewarmed over standard, fast. or slow tim e periods. After deep hypothermia (24 degrees C for 2 hours) the animals we re rewarmed in a standard, fast, slow, or stepwise manner. Cerebral blood f low (CBF), extracellular glutamate, and lactate were monitored. Hippocampal CA1 cell damage was assessed 7 days after induction of ischemia. In animals treated with moderate hypothermia, the rewarming rate had no inf luence on the number of surviving neurons. However, fast rewarming from dee p hypothermia (to 37 degrees C for 30 minutes) failed to provide the neurop rotective effect of hypothermia. Furthermore, this group showed a poor reco very of CBF (p < 0.01) and, consequently, an increase in extracellular glut amate (p < 0.01) and lactate (p < 0.01) in the hippocampus. Conclusions. The results of this study indicate a transient uncoupling of C BF and cerebral metabolism during fast rewarming from deep hypothermia, whe reas slow and stepwise rewarming periods were found to be useful for protec tion against uncoupling of CBF and cerebral metabolism Juring rewarming.