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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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

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