The neuromuscular transmission module versus the relaxometer mechanomyograph for neuromuscular block monitoring

The neuromuscular transmission module (M-NMT) is an integrated piezoelectric motion sensor module incorporated in the AS/3(TM) anesthesia monitor. We compared the neuromuscular block of 0.6 mg/kg rocuronium (twice the 95% effective dose) monitored by the M-NMT with that monitored by the Relaxometer mechanomyograph (MMG). The two monitors were alternately allocated to the left or right hands of 20 patients. T-1%, the first twitch of the train-of-four (TOF), and the TOF ratio (T-4/T-1) were used for evaluating the neuromuscular block. There was no significant difference in the mean (min) +/- SD onset time or time to 0.8 TOF ratio recovery measured by the M-NMT (1.5 +/- 0.3, 49.4 +/- 8.1) compared with MMG (1.8 +/- 0.6, 50.9 +/- 9.9), respectively. However, the time (min) to 25% T-1 recovery was significantly longer when monitored by the M-NMT (25.6 +/- 8) than by the MMG (20.2 +/- 6.3). During recovery from neuromuscular block, the difference between the TOF ratios measured by the two monitors showed a bias of -0.031, and the limits of agreement (bias +/-1.96 SD) were -0.281 and +0.22. The M-NMT monitor could determine the time to tracheal intubation as well as full recovery from neuromuscular block, but it lagged behind the MMG in determining the time to rocuronium repeat dose administration.