Background: There have been no evidence-based comparisons of motor-evoked potential (MEP) monitoring with no and partial neuromuscular block (NMB). We compared the effects of different levels of NMB including no NMB on MEP parameters.
Methods: MEP-monitored 120 patients undergoing neurosurgery were enrolled. The patients were randomly allocated to four groups: Group A was to maintain two train-of-four (TOF) counts; Group B was to maintain a T(1)/Tc of 0.5; Group C was to maintain a T(2)/Tc of 0.5 (T(1,2), first or second twitch height of TOF; Tc, control twitch height); Group D did not maintain NMB. The mean MEP amplitude, coefficient of variation (CV), the incidence of spontaneous respiration or movement, the efficacy of MEP, and haemodynamic parameters were compared.
Results: The median [inter-quartile range (IQR)] amplitudes of the left leg for Groups A, B, C, and D were 0.23 (0.15-0.57), 0.44 (0.19-0.79), 0.28 (0.15-0.75), and 0.75 (0.39-1.35) mV, respectively. The median (IQR) CVs of the left leg were 71.1 (56.9-88.8), 76.1 (54.2-93.1), 59.8 (48.6-95.6), and 25.2 (17.3-35.0), respectively. The differences between groups of the mean amplitudes of the left arm and both legs were statistically significant (Kruskal-Wallis test, P=0.011 for the left leg). For all limbs, the differences between groups of the CVs were significant (P<0.001, for the left leg). Other parameters were not different.
Conclusions: If NMB is used during MEP monitoring, a target T(2)/Tc of 0.5 is recommended. In terms of the MEP amplitude and variability, no NMB was more desirable than any level of partial NMB.