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TECHNOLOGY, COMPUTING, AND SIMULATION

Video Imaging to Assess Neuromuscular Blockade at the Larynx

Keith J. Girling, FRCA^*, Jennifer L. Spendlove, BSc^*, Muhammad S. Quraishi, FRCS, and Ravi P. Mahajan, MD^*

*University Department of Anaesthesia and Intensive Care, Queen’s Medical Centre, and City Hospital, Nottingham, and Department of Otolaryngology, Queen’s Medical Centre, Nottingham

Address correspondence and reprint requests to Keith Girling, FRCA, Adult Intensive Care Unit, Queen’s Medical Centre, Nottingham NG7 2UH, UK. Address e-mail to Keith.Girling{at}nottingham ac.uk.

We describe video imaging as a technique for assessing neuromuscular blockade at the larynx. We sought to determine the stability and reproducibility of this technique and to compare the effect of succinylcholine at the adductor pollicis and the larynx. Ten patients were studied. Anesthesia was induced and maintained with propofol. The recurrent laryngeal nerve was stimulated superficially and movements of the vocal cords were recorded on videotape by using a fiberoptic bronchoscope passed via a laryngeal mask airway. Neuromuscular function was recorded at the adductor pollicis by using a mechanomyograph. Twenty images of the vocal cords were examined repeatedly by one investigator and by ten independent observers. The mean difference between the two sets of observations was 0.86 degrees with a correlation coefficient (r) of 0.997. For 3 min before the administration of relaxant the coefficient of variation in the cord movement during supramaximal stimulation ranged from 1%–4% (median 2.7%). After the administration of succinylcholine 1 mg · kg^-1 the times to loss of T1 at the larynx and hand were 63 ± 15 s and 63 ± 12 s respectively. Times to 25% recovery were 215 ± 36 s at the larynx and 436 ± 74 s at the hand and times to 75% recovery were 285 ± 55 s and 525 ± 85 s respectively. These results indicate that video imaging may be a useful research technique for estimating neuromuscular blockade at the larynx and that the time to onset of succinylcholine at the larynx is similar to that at the hand, whereas the duration of blockade is significantly shorter at the larynx.

Implications: Assessment of neuromuscular blockade at the larynx is possible by using a video imaging technique. By using this technique, the time to onset of neuromuscular blockade at the larynx is similar to that at the hand after the administration of succinylcholine; this finding is different from previously published data obtained by using a cuff pressure measurement technique.

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