脊椎脊髄手術中MEPモニタリングにおける末梢神経刺激CMAP補正の有用性—特にanesthetic fade補正に関して—

<p>  Background : We normalized the amplitude of motor-evoked potential (MEP) monitoring using compound muscle action potential (CMAP) generated by peripheral nerve stimulation. Anesthetic fade refers to a time-dependent decrease in the amplitude of intraoperative MEP. It is thought to result from the accumulation of propofol. We examined whether normalization by CMAP after peripheral nerve stimulation could increase the sensitivity and specificity of MEP monitoring and compensate for anesthetic fade during spinal surgery. </p><p>  Methods : Intraoperative MEP monitoring was performed in 382 spinal operations in patients without distinct preoperative motor palsy. Sensitivities and specificities with or without CMAP normalization were calculated using the receiver operating characteristic (ROC) analysis. In 1400 muscles in 378 spinal surgeries, which did not exhibit neurological motor changes after the operation, the MEP amplitude and the CMAP amplitude according to operation times were analyzed.</p><p>  Results : In 382 spinal surgeries for patients without distinct preoperative motor palsy, amplitude reductions of 77.9% and 80.6% as cutoff points for motor palsy with and without CMAP normalization resulted in a sensitivity of 100% and specificity of 96.8% and 96.5%, respectively. In 1400 muscles in 378 spinal surgeries, which did not exhibit neurological motor changes after the operation, the amplitudes of both MEP and CMAP increased over time after peripheral nerve stimulation due to the disappearance of muscle-relaxant action. After peripheral nerve stimulation, CMAP significantly increased from the beginning to the end of the operation. Anesthetic fade in transcranial MEP monitoring seemed to occur at more than 300min of surgery based on the results of a ROC analysis of the operation time and relative amplitudes. While the mean amplitude without CMAP normalization at more than 300min was significantly lower than that at less than 300min, the mean amplitude with normalization by CMAP after peripheral nerve stimulation for more than 300min was not significantly different from that at less than 300min.</p><p>  Conclusions : Although CMAP after peripheral nerve stimulation normalization did not increase the sensitivity and specificity of MEP monitoring during spinal surgery, it was able to avoid the effect of anesthetic fade. Anesthetic fade seemed to result from a decrease in synaptic transmission at the neuromuscular junction due to propofol accumulation.</p>