The effect of profound levels of hypothermia (below 14 degrees C) on canine cerebral metabolism.

The goal of this study was to determine the temperature coefficient (Q10) for canine CMRO2 at temperatures below 14 degrees C. Eight dogs were anesthetized with halothane for surgical preparation. The animals were placed on total cardiopulmonary bypass and CBF was measured by direct sagittal sinus outflow. Duplicate measurements were taken at 37, 13, and 7 degrees C. The EEG became isoelectric at a temperature of 12.0 +/- 0.8 degrees C. The Q10 between 13 and 7 degrees C was 2.19 +/- 0.59. With rewarming to 37 degrees C, cerebral metabolic variables returned to control levels. Brain biopsies taken at the end of the study yielded normal values for brain energy stores. We conclude that the Q10 for CMRO2 at temperatures between 7 and 37 degrees C can be profoundly affected by the state of cerebral function as reflected by the EEG. In the absence of EEG activity, an expected Q10 value of 2.2 reflects only the direct effect of temperature on the rates of biologic reactions.