Video imaging to assess neuromuscular blockade at the larynx

We describe video imaging as a technique for assessing neuromuscular blocka de at the larynx. We sought to determine the stability and reproducibility of this technique and to compare the effect of succinylcholine at the adduc tor pollicis and the larynx. Ten patients were studied. Anesthesia was indu ced and maintained with propofol. The recurrent laryngeal nerve was stimula ted superficially and movements of the vocal cords were recorded on videota pe by using a fiberoptic bronchoscope passed via a laryngeal mask airway. N euromuscular function was recorded at the adductor pollicis by using a mech anomyograph. Twenty images of the vocal cords were examined repeatedly by o ne investigator and by ten independent observers. The mean difference betwe en the two sets Of observations was 0.86 degrees with a correlation coeffic ient (r) of 0.997. For 3 min before the administration of relaxant the coef ficient of variation in the cord movement during supramaximal stimulation r anged 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 blo ckade at the larynx and that the time to onset of succinylcholine at the la rynx is similar to that at the hand, whereas the duration of blockade is si gnificantly shorter at the larynx.