[Measuring muscle relaxation with mivacurium in comparison with mechano- and electromyography]

Based on survey of the literature, methodological problems of electromyographic and mechanomyographic neuromuscular monitoring are presented. Often mechanomyography (MMG) is accompanied by mechanical problems during the registration of the contractions in the operating theatre. In contrast to mechanomyography the registration of electromyographic signals is easier whereas the processing of electromyographic signals is more difficult. In the operating theatre, registration problems can also occur with electromyography (EMG) from artefacts arising from stimulation impulses, high frequency apparatus and alternating current. During neuromuscular monitoring using MMG, a positive drift of the amplitudes of the contractions can be observed, whereas EMG leads to a negative drift of the amplitudes of the action potentials. Both observations can lead to misinterpretation of the degree of neuromuscular block measured by single twitch stimulation during the recovery period. Both the positive and negative drifts can be prevented by single twitch stimulation lasting for up to 10 minutes before the start of the neuromuscular monitoring of the effect of a given dose of a muscle relaxant. Finally, a clinical study of simultaneous registration of the MMG at the M. adductor pollicis and of the EMG at the M. interosseus dorsalis DI under total intravenous anaesthesia using propofol and alfentanil and muscle relaxation with a bolus dose of 75 mg/kg mivacurium is described. During the mechanomyographic studies, a decrease in the preload by an average of 1.2 Newton (N) with a maximum level of 4.0 N occurred. The decrease in preload was less than 25%. The mechanomyographically measured onset time of an ED95 of mivacurium amounted to 3.5 +/- 1.2 minutes on average and the degree of maximum neuromuscular block on average (95.1 +/- 5.6%) tallied very well with the expected value of 95.0%. The electromyographically measured onset time of an ED95 of mivacurium amounted to 4.3 +/- 1.2 minutes on average and the degree of maximum neuromuscular block amounted to only 91.3 +/- 8.1% on average. A comparison of the mechanomyographic values and the electromyographic values leads to the following results: the MMG showed a significantly shorter onset time (p < 0.0001) and a significantly deeper maximum neuromuscular block (p = 0.0004) than the EMG. There were also significant differences between mechanomyographically and electromyographically measured recovery values regarding T1(75) (p = 0.0007), T1(90) (p < 0.0001), TOF0.8 (p = 0.0386) and T1(25-75) (p < 0.0001). On average, an ED95 of mivacurium showed a significantly slower recovery in the mechanomyogram than in the electromyogram.