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 (T₁) to the control T₁ before administration of rocuronium (T₁c) and train-of-four ratios (TOFRs) were compared using repeated measures Bland–Altman analysis.

Results

Among the 2419 paired T₁/T₁c differences where the average T₁/T₁c 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 T₁/T₁c 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 T₁/T₁c and TOFR differences, Lin's concordance correlation coefficients were 0.98 and 0.995, respectively. Repeatability coefficients for T₁/T₁c 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.