Reversibility of transient focal cerebral ischemia evaluated by somatosensory evoked potentials in cats

We designed this study to determine whether somatosensory evoked potentials (SEP) could be a reliable indicator to detect development of cerebral infarction or to predict reversibility of cerebral ischemia by investigating relationship among SEP, local cerebral blood flow (l-CBF), and histological changes after transient occlusion of the middle cerebral artery (MCA) in 36 cats. In 24 cats (group 1), gradual recovery of the cortical SEP was observed despite continued MCA occlusion, whereas the SEP remained lost in the remaining 12 cats (group 2). In group 1, amplitude of cortical SEP recovered completely 6 hours after recirculation following 30, 60, or 120 minutes of MCA occlusion, and only one developed cortical infarction. In six cats of group 2, the circulation was restored after 30 minutes of MCA occlusion. All showed complete recovery of SEP amplitude and none developed cortical infarction. When the MCA occlusion lasted 60 minutes in the remaining six cats, there was no recovery of the SEP amplitude and large cortical infarction was found in all six cats. Our findings suggest that SEP is a useful monitor for detecting cerebral infarction after MCA occlusion and that the critical time to avoid cerebral infarction would be 30 minutes when cortical SEP remains lost.