Somatosensory evoked responses during and after graded brain ischaemia in goats

Somatosensory evoked potentials (SEPs) were studied during graded incomplete cerebral ischaemia in eight goats and for the following 2 h. Anaesthesia was maintained with etomidate 1-1.5 mg kg-1 h-1 and 50% nitrous oxide in oxygen. Global cerebral blood flow (gCBF) was measured by a magnetic flow transducer at one internal maxillary artery after surgical occlusion of all other major extracranial cerebral arteries. CBF was reduced every 30 min by 25% with a lower limit of 15-20 ml 100 g-1 min-1. Regional cerebral blood flow (rCBF) in the brainstem and cortex was measured by the microsphere technique. The main findings were: (a) a graded decline in cortical SEP and a concurrent prolongation of the central conduction time (CCT) at gCBF values below 35 ml 100 g-1 min-1 and (b) an incomplete recovery of cortical SEP components during recirculation. Reduction of gCBF affected cortical rCBF more severely than brainstem rCBF. As a result, only cortical SEPs were changed. Our data suggest that reduced cerebral perfusion may result in altered cortical brain electrical activity that may be monitored by SEP recordings.