Phonomyography as a novel method to determine neuromuscular blockade at the laryngeal adductor muscles: comparison...

Neuromuscular blockade at the laryngeal adductor muscles may be measured using the cuff of a endotracheal tube placed between the vocal cords. Phonomyography is an alternative method of neuromuscular monitoring. In this study, phonomyography is applied to determine blockade at the larynx and compared with the cuff pressure method.

After the authors obtained approval from the ethics committee and informed consent, 28 patients were entered in the study. After induction of anesthesia, a endotracheal tube was inserted. Its cuff was placed in the trachea in routine fashion (n = 14) or between the vocal cords (n = 14). In all patients, a small condenser microphone was placed in the vestibular fold, just lateral to the tube, next to the laryngeal adductor muscles. The recurrent laryngeal nerve was stimulated supramaximally with single twitch stimulation (0.1 Hz) for onset, and train-of-four stimulation every 12 s during offset of neuromuscular blockade was produced by 0.1 mg/kg mivacurium. Onset and recovery of neuromuscular blockade measured by the two methods were compared using the test (P < 0.05), and a Bland-Altman test was performed to define agreement between the two methods. Onset and recovery of neuromuscular blockade measured by phonomyography with the cuff placed between the vocal cords or in the trachea were compared using the test (P < 0.05).

Mean onset, maximum effect, and time to reach 25% and 75% of control twitch response for phonomyography cuff pressure method were 145 s (SD, 25) 156 s (SD, 33), 89% (SD, 4) 91% (SD, 4), 9 min (SD, 4) 10 min (SD, 3), and 27 min (SD, 4) 29 min (SD, 4), respectively, without being significantly different. Mean bias was -2%, with limits of agreement of -20 and +18% for all signals (cuff method minus phonomyography). There was no significant difference in onset and offset of neuromuscular blockade measured using phonomyography with the cuff placed between the vocal cords or in the trachea.

Both methods can be used interchangeably to determine neuromuscular blockade of the laryngeal adductor muscles. Phonomyography allows measurement of laryngeal blockade with the endotracheal tube in the normal position.