SOMATOSENSORY-EVOKED POTENTIAL MONITORING IN CERVICAL SURGERY - IDENTIFICATION OF PREOPERATIVE AND INTRAOPERATIVE RISK-FACTORS ASSOCIATED WITH NEUROLOGICAL DETERIORATION

Cortical and subcortical somatosensory evoked potentials (SSEPs) were noninvasively monitored in 191 surgical procedures involving the cervi cal spine. In nine patients in the poorest neurological condition, SSE Ps could not be monitored. Lower limb SSEPs were often too degraded to be useful. Upper limb responses were reliably recorded in 182 procedu res, with a sensitivity of 99% and a specificity of 27% in 10 patients who developed neurological signs postsurgery. The aim of monitoring w as to detect changes in spinal cord function at a time when neurologic al deterioration could be prevented or reversed, and these studies ale rted the authors to certain clinical and SSEP risk factors associated with deterioration. Clinical and operative risk factors were: 1) poor preoperative neurological function (one-third of Ranawat Class IIIb pa tients deteriorated); 2) use of instrumentation (the risk doubled in p reoperatively unimpaired patients); 3) upper cervical and clival surge ry (the risk tripled); and 4) and multisegmental surgery (increased ri sk with each additional level). There were SSEP changes in 33 patients . Fifty percent of patients with a complete loss had neurological dama ge, unlike those who had incomplete loss or whose electrical changes h ad recovered by the end of surgery. In the authors' view these ''false positives'' may represent real physiological changes, the effects of which might have been minimized by an alteration in the surgeon's resp onse as a result of the warning. Although these initial studies have m ade this surgical team more alert to potential problems, the role of i ntraoperative SSEP monitoring is still being debated.