Intraoperative neurophysiological monitoring using somatosensory evoked potentials has been linked to a reduction in the incidence of neurological deficits during corrective surgery. Nonetheless, quantitative assessments of somatosensory evoked potential waveforms are often difficult to evaluate, because they are affected by anesthesia, injury, and noise. Here, we discuss a novel method that integrates somatosensory evoked potential signals into a single metric by calculating the area under the curve (AUC).
Thirty-two Sprague-Dawley rats underwent a laminectomy procedure and were then randomly assigned to a control group or to receive a contusive spinal cord injury ranging from 100 to 200 kilodynes. Neurophysiological testing was completed at various points perioperatively and postoperatively. Somatosensory evoked potential traces obtained were processed and the AUC metric was calculated.
The AUC significantly decreased to 11% of its baseline value after impact and remained at 25% baseline after 1 hour for the 200-kdyn cohort. Postimpact, AUC for the control versus the 150-kdyn and 200-kdyn groups, and the 150-kdyn versus 200-kdyn groups were significantly higher (P < 0.01, P < 0.001, and P < 0.05, respectively). Across days, the only significant parameter accounting for AUC variability was impact force, P < 0.0001 (subject parameters and number of days were not significant).
The AUC metric can detect an iatrogenic contusive spinal cord injury immediately after its occurrence. Moreover, this metric can detect different iatrogenic injury impact force levels and identify injury in the postoperative period. The AUC integrates multiple Intraoperative neurophysiological monitoring measures into a single metric and thus has the potential to help clinicians and investigators evaluate spinal cord impact injury status.
*Department of Neurological Surgery, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, U.S.A.; and
†Department of Neurosurgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, Arizona, U.S.A.
Address correspondence and reprint requests to Parthasarathy Thirumala, MD, Department of Neurological Surgery, Center of Clinical Neurophysiology, University of Pittsburgh, 3550 Terrace St, Pittsburgh, PA 15213; e-mail: email@example.com.
The Copeland Grant from the Department of Neurological Surgery at the University of Pittsburgh provided funding for this research.
The authors have no conflicts of interest to disclose.