244. Impact of inhalational anesthetic agents on the baseline monitorability of motor evoked potentials (MEPs) during spine surgery: A review of 22,755 cervical and lumbar procedures

Abstract

<h3>BACKGROUND CONTEXT</h3> During spine surgery, motor evoked potentials (MEPs) are often utilized to monitor both spinal cord function and spinal nerve root or plexus function. While there are reports evaluating the impact of anesthesia on the reliability of MEPs to monitor spinal cord function, less is known about the impact of anesthetics on the ability of MEPs to monitor spinal nerve root and plexus function. <h3>PURPOSE</h3> To compare the baseline monitorability and amplitude of MEPs during cervical and lumbar procedures between two cohorts based on the maintenance anesthetic regimen: a total intravenous anesthesia (TIVA) vs a regimen balanced with volatile inhalational and intravenous agents. <h3>STUDY DESIGN/SETTING</h3> Baseline MEP data from a total of 16,559 extradural cervical and 6,196 lumbar spine procedures utilizing multimodality intraoperative neuromonitoring (IONM) including MEPs between January 2017 and March 2020 were obtained from a multi-institutional database. Two cohorts were delineated based on the anesthetic regimen: a TIVA cohort and a balanced anesthesia cohort. <h3>PATIENT SAMPLE</h3> Age 18 and older. <h3>OUTCOME MEASURES</h3> Percent monitorability and amplitudes of baseline MEPs. <h3>METHODS</h3> The baseline monitorability of each muscle MEP was evaluated by the IONM team in real time and recorded in the patient's electronic medical record. The relation between anesthetic regimen and baseline monitorability was estimated using mixed effects logistic regression, with distinct models for cervical and lumbar procedures. Subsets of cervical and lumbar procedures from each anesthesia cohort in which all MEPs were deemed monitorable were randomly selected and the average peak-to-trough amplitude of each muscle MEP was retrospectively measured. Mixed-effects linear regression models were estimated (one each for cervical and lumbar procedures) to assess possible differences in average amplitude associated with anesthesia regimen. <h3>RESULTS</h3> At the time of surgery, baseline MEPs were reported as monitorable from all targeted muscles in 86.8% and 83.0% of cervical and lumbar procedures, respectively, for the TIVA cohort, but were reported as monitorable in just 59.3% and 61.0% of cervical and lumbar procedures, respectively, in the Balanced cohort, yielding disparities of 27.5% and 22.0%, respectively. The model-adjusted monitorability disparity between cohorts for a given muscle MEP ranged from 0.2% -16.6% but was smallest for distal intrinsic hand and foot muscle MEPs (0.2%-1.1%) and was largest for proximal muscle MEPs (deltoid: 10.8%, biceps brachii: 8.8%, triceps: 13.0%, quadriceps: 16.6%, gastrocnemius: 7.8%, and tibialis anterior: 3.7%) where the monitorability was significantly decreased in the Balanced cohort relative to the TIVA cohort (P < 0.0001). Relative to the TIVA cohort, the model-adjusted amplitude of an MEP in the Balanced cohort was smaller for all muscles measured, ranging from 27.5%-78.0% smaller. Relative to the TIVA cohort, the model-adjusted amplitude of an MEP was significantly decreased (P <0.01) in the Balanced cohort for the most proximal muscles (percent smaller: deltoid: 74.3%, biceps: 78.0%, triceps: 54.9.0%, quadriceps: 54.8%). <h3>CONCLUSIONS</h3> TIVA is the preferred anesthetic regimen for optimizing MEP monitoring during spine surgery. Inhalational agents significantly decrease MEP monitorability and amplitudes for most muscles, and this effect is especially pronounced for proximal limb muscles such as the deltoid, biceps, triceps, and quadriceps. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.