Feasibility of F-Waves Monitoring Under General Anesthesia With Remimazolam: A Prospective Observational Study.

BACKGROUND: F-waves are produced by the re-excitation of spinal anterior horn cells following distal electrical stimulation without being mediated through a conventional monosynaptic reflex pathway. F-waves can often be recorded even when voluntary motor output is limited and have been investigated as an adjunctive modality for intraoperative neurophysiological monitoring. However, some anesthetic agents affect intraoperative spinal neuromonitoring. Remimazolam is a novel, relatively safe anesthetic agent, especially for older adults, and its effects on F-waves are unclear. Therefore, we aimed to assess F-waves in patients undergoing spine and spinal cord surgery under remimazolam anesthesia. METHODS: We prospectively evaluated 25 patients scheduled for prolonged spine or spinal cord surgery (≥3 h). F-waves were intraoperatively recorded from the left abductor hallucis at baseline and hourly thereafter. The persistence, normalized minimum latency, and amplitudes of the F-waves and F/M amplitude ratio were determined. In addition, their longitudinal changes under remimazolam anesthesia were assessed using linear mixed-effects models. Multivariable linear regression analysis was performed to identify factors associated with a change in F-wave persistence at 3 hours. Age, preoperative manual muscle test score, and baseline persistence were included as covariates. RESULTS: None of the F-wave parameters showed significant time-dependent changes. The preoperative manual muscle test result was not an independent predictor of the change in F-wave persistence observed in the multivariable model. CONCLUSIONS: F-waves remained recordable without significant time-dependent changes in most patients under remimazolam anesthesia for up to 3 hours, suggesting that remimazolam has minimal effects on F-wave recordings.