Neuromuscular blocking drugs open the vocal cords and facilitate mask ventilation but may impede the return to spontaneous breathing. Current German S1 airway management guidelines recommend short-acting neuromuscular blocking drugs such as succinylcholine for at-risk patients without defining doses or methods to monitor vocal cord opening. This study investigates the relationship between electromyography-based single twitch response amplitude and vocal cord opening. Secondary endpoint was the quantification of succinylcholine's neuromuscular blocking effect after administration of 0.1 and 0.9 mg kg−1 IBW.

Thirty patients aged ≥18 years scheduled for surgery with tracheal intubation using succinylcholine were enrolled. Induction of anaesthesia included remifentanil and propofol. The depth of anaesthesia was measured with an electroencephalogram monitor. The baseline neuromuscular block was determined electromyographically with single twitch stimulation of the ulnar nerve at the abductor digiti minimi muscle. The vocal cord area was videorecorded to determine baseline conditions. Then, the patient received 0.1 mg kg−1 IBW succinylcholine and additional 0.9 mg kg−1 IBW after 2 min. After 4 min the trachea was intubated.

Pearson's correlation coefficient between the variables of the primary endpoint was −0.54 ± 0.09 (P < 0.001). The non-linear regression including interactions with a sedation-depth-index estimated accurately the vocal cord opening (R2 68.3 %, P < 0.001). Succinylcholine 0.1 mg kg−1 opened the vocal cords 78 % (IQR 65–86 %).

After succinylcholine administration, the electromyographic single twitch stimulation combined with sedation-depth monitoring reliable estimates vocal cord aperture. The considerable vocal cord opening achieved after 0.1 mg kg−1 succinylcholine supports using lower doses for assuring mask ventilation.

DRKS00021433.

Quantitative neuromuscular blocking drug monitoring

Single twitch stimulation

Succinylcholine

Tracheal intubation

Vocal cords

© 2025 The Authors. Published by Elsevier Ltd.