Relationship between evoked potentials and clinical status in spinal cord ischemia.

Abstract

Sciatic neurogenic motor-evoked potentials (sciatic-NMEP), spinal-evoked potentials (spinal-EP), and somatosensory-evoked potentials (SEP) were recorded in the lumbar cord during progressive ligation of segmental arteries. Relationship between electrophysiologic assessment and clinical status was studied. In 12 anesthetized dogs that had arterial ischemia of the lumbar cord produced by ligation of segmental arteries, the aforementioned evoked potentials were recorded, and their presence or absence was compared with the clinical status of repeated wake-up tests. Both sciatic-NMEP loss and ligation level producing cord ischemia were not associated with severity of wake-up test. Sciatic-NMEPs were lost earlier than spinal-EP and SEPs after progressive ligation. The false-negative rate of sciatic-NMEP, SEP at high spine and at low spine was 12.5%, 20.8%, and 41.7%, respectively. The waveform morphology of potentials by cord ischemia decreased in amplitude and in the number of peaks without a shift of latency. First, baseline NMEPs and SEPs were obtained, lumbar arteries were ligated, evoked potentials were recorded continuously, and wake-up test was administered. If sciatic-NMEPs were not lost, intercostal arteries were ligated, and potentials and clinical status were reassessed. Though these results were complicated, sciatic-NMEP was more sensitive to the spinal cord ischemia and a better predictor of clinical outcome than spinal-EP and SEP. However, the presence was not a guarantee of normal function. Somatosensory-evoked potentials are not a good predictor of clinical motor status. The initial morphologic change of these potentials secondary to ischemia consisted of a decrease in amplitude and in the number of peaks without a shift of latency. The peripheral-NMEP is a better warning system to spinal cord ischemia and its adoption may prevent cord ischemia during surgery, whereas SEP and spinal-EP can not be indicies.