Effect of Compound Muscle Action Potential After Peripheral Nerve Stimulation Normalization on Anesthetic Fade of Intraoperative Transcranial Motor-Evoked Potential

Abstract

Purpose: Anesthetic fade refers to the time-dependent decrease in the amplitude of the intraoperative motor-evoked potential. It is thought to be caused by the accumulation of propofol. The authors examined whether normalization by the compound muscle action potential (CMAP) after peripheral nerve stimulation could compensate for anesthetic fade.Methods: In 1,842 muscles in 578 surgeries, which did not exhibit a motor-neurologic change after the operation, the motor-evoked potential amplitude was normalized by the CMAP amplitude after peripheral nerve stimulation, and the CMAP amplitude and operation times were analyzed.

Anesthetic Fade in Intraoperative Transcranial Motor Evoked Potential Monitoring Is Mainly due to Decreased Synaptic Transmission at the Neuromuscular Junction by Propofol Accumulation

“…The observation that the AF in both craniotomy and spinal surgery could be avoided by CMAP after peripheral nerve stimulation normalization suggests that the main cause of AF is a decrease in synaptic transfer of neuromuscular junctions due to propofol accumulation. 10,20,21 Conclusions AF of tcMEP occurred in both craniotomy and spinal cord surgery, and it was also corrected by CMAP after peripheral nerve stimulation although it is necessary to consider changes in transcranial stimulation conditions due to craniotomy. As we reported previously, AF is considered to be mainly due to a decrease in the synaptic transfer of the neuromuscular junction due to the accumulation of propofol because of the avoidance by CMAP normalization.…”

“…4,11,12 Our report that AF could be avoided by CMAP after peripheral neurostimulation normalization included both spinal and cranial surgery. 10 In this study, AF was examined separately for craniotomy and spinal surgery, and a stronger amplitude reduction of tcMEP was observed earlier in craniotomy than in spinal surgery. In tcMEPs during craniotomy, the elimination of cerebrospinal fluid may cause air to enter apart from the skull and motor cortex, and the amplitude may be significantly reduced.…”

“…Lyon et al reported an increase in the stimulus threshold, 4 but in subsequent examinations, evaluation by lowering the amplitude was carried out. [10][11][12] To date, reports on AF have mostly been about spinal surgery. 4,11,12 Our report that AF could be avoided by CMAP after peripheral neurostimulation normalization included both spinal and cranial surgery.…”

“…As previously mentioned, since AF could be avoided by CMAP after peripheral nerve stimulation, the main cause of AF was the decrease in synaptic transfer at the neuromuscular junction due to propofol accumulation. 10 Although it has generally been thought that propofol has no muscle relaxant effect, there have been several reports of propofol lowering synaptic transfer at neuromuscular junctions. 20,21 The components of tcMEP will be examined in order.…”

“…[5][6][7][8] We previously reported that normalization of tcMEP amplitude by compound muscle action potential (CMAP) after peripheral nerve stimulation prevented the expression of AF, suggesting that AF might be due to reduced synaptic transfer in the neuromuscular junction. 9,10 In addition, although we previously examined a group of patients who underwent both cranial and spinal surgery, studies on AF have been entirely on patients undergoing spinal surgery, and there has been no report on AF in tcMEP monitoring during cranial surgery and in dMEP by stimulation to motor area or spinal cord. 4,[11][12][13] To consider the causes of AF, we compared the expression and avoidance by CMAP normalization of AF in craniotomy versus spinal surgery, and in muscles of the upper versus lower limbs.…”