Area under the curve and amplitude of the compound motor action potential are clinically interchangeable quantitative measures of neuromuscular block: a method comparison study.

Background: Current guidelines recommend quantitative neuromuscular block monitoring during neuromuscular blocking agent administration. Monitors using surface electromyography (EMG) determine compound motor action potential (cMAP) amplitude or area under the curve (AUC). Rigorous evaluation of the interchangeability of these methods is lacking but necessary for clinical and research assurance that EMG interpretations of the depth of neuromuscular block are not affected by the methodology.

Methods: Digitised EMG waveforms were studied from 48 patients given rocuronium during two published studies. The EMG amplitudes and AUCs were calculated pairwise from all cMAPs classified as valid by visual inspection. Ratios of the first twitch (T) to the control T before administration of rocuronium (Tc) and train-of-four ratios (TOFRs) were compared using repeated measures Bland-Altman analysis.

Results: Among the 2419 paired T/Tc differences where the average T/Tc was ≤0.2, eight (0.33%) were outside prespecified clinical limits of agreement (-0.148 to 0.164). Among the 1781 paired TOFR differences where the average TOFR was ≥0.8, 70 (3.93%) were outside the prespecified clinical limits of agreement ((-0.109 to 0.134). Among all 7286 T/Tc paired differences, the mean bias was 0.32 (95% confidence interval 0.202-0.043), and among all 5559 paired TOFR differences, the mean bias was 0.011 (95% confidence interval 0.0050-0.017). Among paired T/Tc and TOFR differences, Lin's concordance correlation coefficients were 0.98 and 0.995, respectively. Repeatability coefficients for T/Tc and TOFR were <0.08, with no differences between methods.

Conclusions: Quantitative assessment neuromuscular block depth is clinically interchangeable when calculated using cMAP amplitude or the AUC.