Comparison of Subdermal Needle and Surface Adhesive Stimulating Electrodes for Somatosensory Evoked Potential Monitoring during Anterior Cervical Discectomy and Fusion.

Introduction: Needle stick injuries remain a physical and psychological burden to healthcare workers. Noninvasive surface adhesive stimulating electrodes used to generate somatosensory evoked potentials can help decrease this risk.

Methods: We performed a retrospective observational study of patients who underwent anterior cervical discectomy and fusion (ACDF) surgery to determine the utility and variability of using surface adhesive stimulating electrodes. Our analysis for utility compared alarm (significant changes) frequency, defined by established alarm criteria, between subdermal needle (Group I) and surface adhesive electrodes (Group II). We compared the variability by comparing the frequency of alarms based on establishing baselines during various stages of the procedure.

Results: Between Group I and Group II, no significant differences were found in demographic, age, number of levels decompressed and fused, and length of surgery variability. However, stimulation intensity was significantly higher in Group II. Significant differences in the mean frequency of alarm of cortical, subcortical, and Erb's somatosensory evoked potential (SSEP) responses for the upper extremities between the two groups were only observed for the upper left Erb's point amplitude (p = 0.03) at retraction and upper right cortical amplitude at incision (p = 0.02). The frequency of alarms of the amplitude of left ulnar cortical responses from SSEPs using surface adhesives when baselines were established at the beginning of the procedure, at the time of incision, and at placement of retractors were 13.83 % (±14.08%), 7.50 % (±7.56%) and 3.42 % (±3.48%), respectively. Comparatively, the frequencies of alarms of the amplitude of left ulnar cortical responses from SSEPs using needle electrodes were 18.07 % (±22.85%), 12.13 % (±17.30%) and 7.37 % (±11.82%), respectively. Similar results were observed from frequency for alarms from the right ulnar SSEPs.

Conclusion: This study found little significant difference between the frequencies of alarm in patients who had SSEP responses obtained using surface adhesive electrodes when compared to needle electrodes. This lack of significant difference was observed even when alarms were established at various stages of the surgery before any major manipulation. For short procedures monitoring the upper extremities only, surface adhesive electrodes may provide a reliable alternative to invasive needle electrodes.