Increase in extracellular potassium in the brain during circulatory arrest: effects of hypothermia, lidocaine, and thiopental.

The effect of temperature (37 degrees C, 28 degrees C, and 18 degrees C), 160 mg/kg lidocaine, and 40 mg/kg thiopental on the efflux of cellular potassium in the cerebral cortex during complete global ischemia was examined. Cerebral ischemia was induced in dogs on cardiopulmonary bypass circulation by stopping the pump. Potassium concentration was measured on the brain surface by a valino-mycine-membrane electrode, which in its response corresponded well to an inserted microelectrode. Hypothermia reduced the ischemic potassium efflux rate to about 50 per cent at 28 degrees C, and about 25 per cent at 18 degrees C. At all temperature levels lidocaine caused an additional reduction in the potassium efflux rate of about 50 per cent, probably by reducing membrane ion permeability in accordance with its local anesthetic action. Thiopental had no effect on the potassium efflux during ischemia. This study opens the possibility that lidocaine, like hypothermia, may provide protection of the ischemic brain.