Authors: Dulfer SE, et al.
Anesthesia & Analgesia. September 05, 2025. doi:10.1213/ANE.0000000000007701
This prospective observational study investigated how blood pressure elevation with norepinephrine and ephedrine affects transcranial electrical stimulation muscle-recorded motor evoked potentials (Tc-mMEPs) in patients undergoing spinal surgery. False positive Tc-mMEP warnings are common during intraoperative monitoring, often attributed to low blood pressure, leading clinicians to increase mean arterial pressure (MAP) with vasopressors.
In 25 patients, Tc-mMEPs were recorded from abductor hallucis, tibialis anterior, and hand muscles as MAP was increased from ~60 to 100 mm Hg. Across all muscle groups, a 10 mm Hg MAP rise was associated with 11–18% increases in amplitude and 10–17% increases in area under the curve (AUC). However, after adjusting for anesthetic depth, propofol concentration, and ephedrine use, significant associations persisted mainly in the abductor hallucis muscle. BIS values also rose with higher MAP, suggesting that increased blood pressure may enhance cortical excitability rather than purely improving spinal cord perfusion.
What You Should Know
• Raising MAP with vasopressors is linked to higher Tc-mMEP amplitudes and AUCs.
• Adjustments for anesthetic depth and propofol levels reduced these associations, suggesting cortical effects play a role.
• BIS values increased with MAP elevation, reinforcing the role of cortical excitability.
• Low blood pressure may not be the sole explanation for Tc-mMEP variability, cautioning against routine vasopressor escalation without considering anesthetic depth.
Practice Implication: During spinal surgery, anesthesiologists should recognize that vasopressor-driven blood pressure elevation may influence Tc-mMEPs via cortical excitability as well as perfusion. Optimizing anesthetic depth and monitoring BIS alongside MAP can reduce false positives and guide safer intraoperative neurophysiologic monitoring.
References
Dulfer SE, et al. Anesth Analg. 2025. doi:10.1213/ANE.0000000000007701
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