Detection of motor pathway suppression by transcranial and transesophageal motor-evoked potentials during thoracic epidural anesthesia.

PURPOSE: Transcranial motor-evoked potentials (TcMEPs) are widely used to detect intraoperative spinal motor pathway impairment. We developed a novel transesophageal motor-evoked potentials (TeMEPs) technique that directly stimulates the spinal cord from the esophagus at the lower cervical to upper thoracic level. This study compared the ability of TeMEPs and TcMEPs to detect reversible motor pathway suppression.

METHODS

Ten pigs (25.0 ± 0.6 kg) were anesthetized with propofol and remifentanil. Motor pathway suppression was induced using T9-T10 level thoracic epidural anesthesia. After baseline measurements, 3 mL of 0.2% ropivacaine was administered epidurally, and TcMEPs and TeMEPs were recorded every 6 min for 60 min. Subsequently, 0.375% and 0.75% ropivacaine (3 mL each) were administered at 180-min intervals, with recordings continued every 6 min for 120 min after each dose. Changes in MEP amplitudes relative to baseline were quantified using the inhibitory area under the curve (iAUC), and comparisons were made across concentrations and between modalities.

RESULTS

Thoracic epidural anesthesia induced concentration-dependent suppression of MEP amplitudes. TcMEPs exhibited marked suppression in both upper and lower limbs at all concentrations. In contrast, TeMEPs demonstrated pronounced and concentration-dependent suppression in the lower limbs, whereas upper-limb TeMEPs were relatively preserved, even at higher concentrations. iAUC analysis revealed significantly greater overall suppression in TcMEPs compared with TeMEPs, particularly in the upper limbs, whereas lower-limb suppression was comparable between modalities at higher concentrations.

CONCLUSION

TeMEPs and TcMEPs assess different levels of the motor pathway and TeMEPs may provide a stable assessment of lower-limb motor pathway impairment.