# The electromyographic single twitch stimulation for monitoring the effect of rocuronium on vocal cord opening – a randomised controlled trial

## TL;DR

This study shows that electromyographic single twitch stimulation can reliably predict vocal cord opening after using the drug rocuronium during anesthesia.

## Contribution

The study demonstrates that single twitch amplitude is a reliable, quantitative predictor of vocal cord aperture following rocuronium administration.

## Key findings

- Single twitch amplitude strongly correlates with vocal cord aperture (Pearson’s coefficients -0.58 and -0.74 for 0.3 and 0.9 mg/kg rocuronium, respectively).
- Higher rocuronium doses showed stronger correlations and less inter-patient variability in twitch amplitude decrease.
- Maximum vocal cord aperture was comparable between the two rocuronium dose groups.

## Abstract

The European Society of Anaesthesiology and Intensive Care recommends the use of neuromuscular blocking drugs for tracheal intubation, but the monitoring is difficult, because the parameters are mostly relative values (e.g. Train-of-four ratio), which show no or only weak correlations to the vocal cord aperture. We investigated the predictive effect of the quantitative single twitch (0.3 ms duration supramaximal stimulus, frequency 0.1 Hz) to estimate vocal cord aperture (primary endpoint). Secondarily, we focused on rocuronium dose-related differences between single twitch amplitude and maximum vocal cord aperture.

Thirty-six adult patients undergoing elective surgery with tracheal intubation using rocuronium were included. Patients received remifentanil and propofol for induction of anaesthesia before the neuromuscular block baseline was measured electromyographically using the single twitch stimulation pattern of the ulnar nerve from the abductor digiti minimi muscle. A video-laryngoscope was inserted to document baseline conditions before the patient received either 0.3 or 0.9 mg/kg IBW rocuronium. The vocal cord area was continuously videorecorded for four minutes, before the trachea was intubated.

Thirty-five patients completed the study; 18 received 0.3 and 17 received 0.9 mg/kg IBW rocuronium. Data showed a strong correlation between single twitch amplitude and vocal cord aperture (bootstrapped Pearson’s coefficients, median ± IQR: -0.58 ± 0.22 in rocuronium 0.3 and -0.74 ± 0.18 in rocuronium 0.9 mg/kg IBW; p < 0.001), meaning that the single twitch amplitude may be a reliable predictor of vocal cord opening. The higher rocuronium dose caused a stronger correlation, lower inter-patient variability, and a steeper single twitch decrease, but the effect on the maximum vocal cord aperture was comparable to that in the 0.3 mg/kg IBW rocuronium group.

The quantitative, electromyographic single twitch stimulation pattern can dose-independent predict vocal cord opening after rocuronium administration.

The study was registered at the German Clinical Trials Register on the 10th of July 2020 (DRKS00021433) prior to enrolment of the patients.