Causal factors for position-related SSEP changes in spinal surgery.

Abstract

Somatosensory evoked potentials (SSEPs) are effective in detecting upper extremity positional injuries; however, causal factors for which patient population is most at risk are not well established. To review causal factors for intraoperative SSEP changes due to patient positioning. A case series with retrospective chart analysis was performed. 398 patient charts and intraoperative neurophysiological monitoring data from patients who underwent thoracolumbar and lumbosacral spine surgery were reviewed in a consecutive sequence from 2012 to 2013. Adverse events (AE) with the upper extremity SSEP recordings were compared to the independent variables, sex, positioning, length of procedure, and body habitus. Thoracolumbar and lumbosacral spine surgeries using contemporaneous ulnar and median nerve SSEPs were reviewed. The one-way analysis of variance (ANOVA) test, Chi-square, and independent samples t test were used to determine statistical significance in having an upper extremity SSEP AE to the aforementioned independent variables. The sample consisted of 209 males (52.5%) and 189 females (47.5%) (n=398). AE to the upper extremity SSEP was seen in 44 patients. Sex was found to be statistically significant for isolated ulnar nerve AE (P≤0.001) with males being most at risk (87.5%). AE for isolated median nerve SSEP was statistically significant for supine and prone positions (P=0.043). Length of procedure was statically significant for isolated ulnar nerve SSEP AE (P=0.039). BMI was statistically significant for generalized upper extremity SSEP AE (P=0.016), as well as isolated ulnar SSEP AE (P=0.006), isolated median SSEP AE (P≤0.001) and contemporaneous median and ulnar SSEP AE of the same limb (P≤0.001). Sex, patient positioning, length of procedure, and BMI are determinants for upper extremity neural compromise during thoracolumbar and lumbosacral spine surgeries.