• J Engbaek.
• Department of Anaesthesiology, Herlev Hospital.
• Dan Med Bull. 1996 Sep 1;43(4):301-16.

AbstractIn this study the applicability of the electromyographical method for monitoring neuromuscular transmission during anaesthesia has been investigated. The purpose was to determine the stability and temperature dependence of the EMG and to evaluate and compare EMG area, amplitude and duration during a non-depolarizing neuromuscular block in the tibialis anterior muscle preparation of the cat. Further, in clinical studies the purpose was to investigate differential hand muscle sensitivity to non-depolarizing neuromuscular blocking agents based on the EMG and the standard adductor pollicis mechanomyogram, and to establish the agreement between the electromyographical and the mechanomyographical methods and their relationship to clinical parameters of residual neuromuscular block. For this purpose a new monitoring equipment was developed for simultaneous recording of the evoked mechanomyogram and the surface compound EMG area, amplitude and duration. In the animal studies the EMG was found to be stable with changes less than 10% during 3 hours of stimulation and with a high degree of reproducibility. In contrast, the mechanomyogram proved unstable over time with changes of 35-50% (positive staircase) within minutes after onset of stimulation followed by a slower decline of the response to 70-75% of control. An inverse relationship was found between temperature and both the mechanomyogram and the EMG, the EMG area and duration being more affected (5-7% per degrees C) than EMG amplitude (2-3% per degrees C). During onset and recovery from non-depolarizing neuromuscular block, EMG area and amplitude of the first major negative deflection and of the total compound response both reflected neuromuscular transmission equally. The EMG duration was found to be unsuitable as a predictor of neuromuscular block. In the clinical studies of the hand muscles (adductor pollicis, hypothenar and first dorsal interosseous muscles) small but clinically insignificant differences in EMG-based sensitivity to pancuronium were observed. There was no difference between EMG area and amplitude in the estimated effective doses of pancuronium and roctronium producing 50% and 90% block, respectively (ED50 and ED90), but EMG-based sensitivity of the adductor pollicis muscle was less than when based on mechanomyography. Comparative analysis of first dorsal interosseous EMG and adductor pollicis mechanomyogram during non-depolarizing neuromuscular block was based on the concept of bias (mean difference between the results by the two methods) and limits of agreement (an estimation of how much results obtained with one method are likely to differ from the results of the other method) and evaluated during TOF nerve stimulation. The two methods agreed within acceptable limits during neuromuscular block with estimated bias being less than 2% during onset. A variable bias of 3-7% was observed during recovery, with EMG overestimating block at 25% recovery and underestimating block at 75% and 90% recovery. Limits of agreement were more narrow during onset (+/- 7-8%) than during recovery (+/- 12-17%), EMG area and amplitude equally reflected the degree of neuromascular block. First dorsal interosseous EMG TOF ratio recovered more slowly than TOF ratio of the adductor pollicis mechanomyogram during early recovery. The relationship between the two methods was described as being log-linear, and during late recovery bias between the TOF ratios of the two methods was zero. However, due to the range of deviations between the EMG and the mechanomyogram, EMG TOF ratios down to 0.55 or up to 0.90 in some patients were found to be compatible with adequate recovery of a mechanomyographical TOF ratio of 0.75. Differences between electromyographical and mechanomyographical TOF ratios in their relation to 5 s sustained headlift were only revealed when the TOF ratio was below 0.50-0.60. More patients were then able to perform the test if the TOF ratio was measured from the EMG.(ABSTRACT T

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