Correlation between somatosensory evoked potentials and neuronal ischemic changes following middle cerebral artery occlusion.

In an attempt to determine the usefulness of evoked potentials as a measure of focal cerebral ischemia, we examined somatosensory evoked potentials (SEP's) and morphological neuronal changes in cats following unilateral middle cerebral artery (MCA) occlusion. Fifteen adult cats underwent transorbital occlusion of the MCA under halothane anesthesia. In seven cats the ipsilateral SEP's were abolished after middle cerebral artery occlusion, and did not show any recovery after 6 hours. The same seven cats showed the greatest area of moderate and severe ischemic neuronal changes, ranging from 21 to 64% (mean 39 +/- 14%) of the total ipsilateral cortical area. The remaining eight cats showed a complete flattening or decreased amplitude of the SEP after occlusion, but demonstrated a considerable recovery in the amplitude of the primary cortical potential during the six hours of the study. All these cats had ischemic areas of less than 15% (mean 9 +/- 3%) of the total ipsilateral cortex. These results demonstrate that the disappearance of the SEP and their failure to recover correlate with the extent and degree of histological cerebral ischemia.