The Influence of Depth of Anesthesia on Motor Evoked Potentials Monitoring During Spinal Surgery in Youth: A Single-Center Prospective Study (SCOL Study)

BACKGROUND: Anesthetic agents or some pathophysiological conditions can affect transcranial motor evoked potentials (TcMEP) monitoring. However, the influence of depth of anesthesia on TcMEP reproducibility in youth remains unclear due to limited data. We tested the hypothesis that a deeper level of total intravenous anesthesia (TIVA) can affect surgeon-directed TcMEP reproducibility and the surgical team's interpretation of TcMEP. METHODS: We conducted a single-center, prospective before-and-after study in 150 youths undergoing TIVA for scoliosis surgery with surgeon-directed TcMEP. A combination of propofol and remifentanil was administered to all patients. TIVA was initially maintained at a set bispectral index (BIS) level: mean (range) 60 (55-65) (BIS60). We deepened the anesthesia to a set BIS level: mean (range) of 40 (55-65) (BIS40) before the skin incision. The surgical team recorded and interpreted TcMEP at both BIS levels. The primary outcome was the effect of anesthesia depth (BIS60 vs BIS40) on TcMEP reproducibility and the surgical team's interpretation. The secondary outcome was to compare changes in relativized TcMEP parameters (amplitude and latency) as a percentage at different levels of anesthesia (BIS60 vs BIS40). RESULTS: Surgeons successfully recorded and interpreted TcMEP in all patients on both levels of depth of anesthesia. The mean ± standard deviation TcMEP amplitudes and latencies at BIS40 were statistically significantly different from the initial TcMEP parameters at BIS60 78.7% ± 15.0 (P < .001) for amplitudes, and 102.7% ± 2.9 (P < .001) for latencies. However, these alterations did not affect the surgical team's interpretation of TcMEP and were therefore not clinically significant. CONCLUSIONS: Keeping TIVA within the recommended BIS mean (range) of 40 to 60 (35-65) did not affect TcMEP reproducibility or surgeons' interpretation of TcMEP. Surgeon-directed TcMEP, along with appropriate depth of anesthesia, may represent a promising alternative when neurophysiologists are unavailable.