A comparison of accelerometric monitoring by TOF Watch® SX and electromyographic monitoring by Tetragraph® for recovery from neuromuscular blockade

J Clin Anesth. 2021 Dec;75:110481. doi: 10.1016/j.jclinane.2021.110481. Epub 2021 Aug 10.


Background: Neuromuscular monitoring has become a standard of care for management of anesthesia. While acceleromyography (AMG) is the most common technology used in clinical practice, guidelines suggest that electromyographic (EMG) devices are ideal for quantitative neuromuscular monitoring. The Tetragraph® is an EMG monitor that has recently been marketed.

Study objective: The aim of this study is to assess the agreement during recovery from neuromuscular blockade of this new monitor with the TOF Watch® SX, and to compare intraobserver variability for the two devices.

Design: Single-center, prospective, observational clinical study.

Setting: Operating room.

Patients: Twenty-three patients were enrolled and twenty patients were included in the analysis.

Intervention: A comparison of TOF-ratios measured sequentially from the same hand with the Tetragraph and TOF Watch SX was conducted during spontaneous recovery of neuromuscular function from patients that received rocuronium during surgery.

Main outcome measures: We used Bland-Altman plots for repeated measures to compare TOF-ratios obtained sequentially by the two devices. Subsequent measures with the same device were used to calculate intraobserver variability for each monitor.

Main results: The bias between AMG and EMG for TOF-ratios range between 0.2 and 1.0 was 0.13 (95% CI 0.08 to 0.18) and the limits of agreement (LoA) were - 0.11 (95% CI -0.20 to -0.06) and 0.37 (95% CI 0.32 to 0.46), respectively. Agreement slightly improved for TOF-ratios higher than 0.8 compared with lower TOF-ratios: the bias was 0.12 (95% CI 0.08 to 0.17) and 0.13 (95% CI 0.08 to 0.19), respectively. EMG relative intraobserver variability was lower compared with AMG (2.0%, IQR 0.0% to 4.5% vs. 3.2%, IQR 1.2% to 6.0%, P = 0.001).

Conclusions: Bias between the TOF Watch SX and the Tetragraph TOF-ratios is in line with previous results for AMG and EMG monitors.

Keywords: Anesthesia; MeSH terms; Neuromuscular blockade; Neuromuscular monitoring.

Publication types

  • Observational Study

MeSH terms

  • Anesthesia Recovery Period
  • Humans
  • Neuromuscular Blockade*
  • Neuromuscular Monitoring
  • Neuromuscular Nondepolarizing Agents*
  • Prospective Studies


  • Neuromuscular Nondepolarizing Agents