Authors: Dulfer SE, et al.
Anesthesia & Analgesia. September 05, 2025. doi:10.1213/ANE.0000000000007701
This prospective observational study investigated how blood pressure elevation affects transcranial electrical stimulation muscle-recorded motor evoked potentials (Tc-mMEPs) in 25 patients undergoing spinal surgery. False positive Tc-mMEP warnings are common and often attributed to inadequate blood pressure. Researchers increased mean arterial pressure (MAP) from 60 to 100 mm Hg with norepinephrine and ephedrine, recording amplitudes and area under the curve (AUC) from lower limb and hand muscles every 2 minutes.
A 10 mm Hg increase in MAP correlated with an 11–18% increase in Tc-mMEP amplitude and a 10–17% rise in AUC. The most consistent effects were seen in the abductor hallucis muscle. However, when adjustments were made for bispectral index (BIS), propofol levels, and ephedrine use, many associations weakened, suggesting cortical excitability plays a significant role. Cardiac index changes mirrored MAP effects, while peripheral nerve excitability was unaffected. Notably, MAP elevation also increased BIS values, even after accounting for anesthetic depth.
What You Should Know
• Raising MAP increases Tc-mMEP amplitude and AUC during spinal surgery.
• The abductor hallucis muscle showed the strongest association.
• Adjusting for anesthesia depth attenuates these effects, highlighting cortical excitability.
• MAP elevation also increased BIS values, independent of propofol concentration.
• Peripheral nerve excitability was unaffected.
KEY POINTS
Question: What are the effects of vasopressor-induced arterial blood pressure elevation on transcranial electrical stimulation muscle-recorded motor evoked potentials (Tc-mMEP)?
Findings: Elevation of the mean arterial pressure is associated with significantly higher Tc-mMEP amplitudes, area under the curves, and lower voltage threshold.
Meaning: Elevation of the mean arterial pressure increases Tc-mMEP amplitude and area under the curves (AUC), possibly due to an increase in cortical excitability.
Practice Implication
During spinal surgery, anesthesiologists should recognize that false positive Tc-mMEP warnings may reflect cortical excitability changes rather than inadequate spinal cord perfusion alone. While raising MAP can improve Tc-mMEP signals, it may not always resolve variability. Tailoring vasopressor use alongside careful depth-of-anesthesia management is essential to avoid unnecessary interventions and improve neuromonitoring reliability.
References
Dulfer SE, et al. Anesth Analg. 2025. doi:10.1213/ANE.0000000000007701
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