Propofol Sensitivity Alone Can Cause Alert Level Loss of TcMEP During Corrective Surgery for Adolescent Idiopathic Scoliosis

Introduction: This study aims to investigate the safety and efficacy of a Transcranial motor evoked potential (TcMEP) protocol incorporating the maintenance of intraoperative mean arterial pressure (MAP) >65 and hematocrit (HCT) >25; obtaining a baseline TcMEP prior to incision, and progressive dosing of propofol.

Methods: From 2009-2022, consecutive Adolescent Idiopathic Scoliosis (AIS) patients undergoing deformity corrections using a TcMEP protocol were studied. Inclusion criteria: age (11-49 years), and ≥5 spinal fusion levels. Exclusion criteria: previous surgery, fusion to the pelvis, neurogenic scoliosis, and other deformity related diagnoses.

Results: 510 patients met inclusion criteria with mean age 15.4 (±3.5) years. 86% were female. Mean spinal levels treated and OR time were 9.6(±3.3) and 346.2(±89.4) min, respectively. There were 21 TcMEP alerts (4.1%). Of these, 3 were hypotension related, 9 occurred during deformity correction, 7 were Propofol dose related and 2 indeterminate. None were related to screw placement. In 4 manipulation related alerts, any rod-based deformity correction triggered an alert, leading to placement of in situ contoured rods. These patients were staged, and successful correction achieved 3 weeks later. In all 7 of the Propofol dose related alerts, there were no concurrent confounding factors. Initiation, but not completion, of a wake-up test resolved the alert. Propofol was restarted at a lower dose. No post-op neurologic deficits were encountered. None of our patients reported intra-operative awareness.

Conclusion : For reliable TcMEP monitoring during AIS surgery, our protocol incorporated hemodynamic support, baseline TcMEP reading prior to incision, and progressive Propofol titration. Successful monitoring was achieved in all 510 patients. There were no post-op neurologic deficits or episodes of intro-operative awareness. Of the 21 TcMEP alerts, in 7 cases, Propofol dose reduction led to restoration of baseline potentials. Propofol was determined to be the sole cause of TcMEP loss, and initiation, but not completion of the Wake-Up test, with reduction of the propofol dose, resolved the issue.