Comparison of two muscles using a novel electromyographic device to assess recovery from muscle relaxants in patients undergoing general anaesthesia

Abstract

To ensure adequate reversal of neuromuscular blockade, the Australian and New Zealand College of Anaesthetist's recommends quantitative neuromuscular transmission (NMT) monitoring. Residual neuromuscular blockade (RNMB) is the presence of muscular weakness post extubation, with recovery defined as train-of-four ratios (TOFr) >0.9. The TetraGraphTM is a novel electromyographic NMT monitor. TetraGraphTM application to different muscles may affect the precision for monitoring neuromuscular blockade recovery. Aim(s): This study compared the precision, bias and limits of agreement of the TetraGraphTM at the abductor digiti minimi (ADM), and first dorsal interosseous (FDI) muscles, using train-of-four stimulation of the ulnar nerve. We hypothesised that the TetraGraphTM would have higher precision at the FDI compared to the ADM due to the greater amplitude of the muscle action potential at FDI. Method(s): TetraSensTM electrodes were applied to the ADM and FDI on contralateral hands. Calibration of both TetraGraphsTM was performed concurrently prior to administration of neuromuscular blockade. Simultaneous measurements of TOFr at the muscles were repeated every 20 seconds until full spontaneous recovery or reversal agent administration. Data was analysed from TOFr 0.2-1.0. Precision, bias and limits of agreement of the TetragraphTM at the muscles were compared using Bland-Altman analysis. A smaller repeatability coefficient suggests higher precision. A smaller bias with narrower limits of agreement indicates a stronger agreement, and thus interchangeability between the muscles for TetraGraphTM monitoring. Result(s): We collected a total of 119 sets of repeated comparisons from 27 participants. TOFr were more precisely measured by the TetraGraphTM at the FDI (repeatability coefficient 0.034 (95% confidence intervals (CI) 0.030 to 0.039) than ADM (repeatability coefficient 0.045, 95% CI 0.040 to 0.051) (Table 1). Within the range of TOFr values of clinical interest for excluding RNMB (TOFr >0.9), the TOFr measured by the TetraGraphTM demonstrated a bias of 0.017 (95% CI 0.023 to 0.057) at the ADM compared to the FDI, with limits of agreement of 0.095 to 0.129 (Figure 1). Conclusion(s): The TetraGraphTM was more precise when measuring TOFr at the FDI compared to the ADM, with 95% of consecutive measurements differing by 0.034. For TOFr >0.9, the ADM demonstrated a small positive bias (0.017) with wide limits of agreement (-0.095 to 0.129) compared to the FDI. Despite a small bias, TOFr measured by the TetaGraphTM at the muscles are not interchangeable due to the wide limits of agreement. When using the TetraGraphTM monitoring at the FDI is suggested in preference to the ADM.