MIVACURIUM NEUROMUSCULAR BLOCK AT THE ADDUCTOR MUSCLES OF THE LARYNX AND ADDUCTOR POLLICIS IN HUMANS

Background: Laryngeal muscles must be paralyzed for tracheal intubatio n. Time to peak effect (onset time) is shorter and intensity of blocka de is Less at laryngeal muscles compared with the adductor pollicis. T he authors' aim in this study was to determine the neuromuscular effec ts of mivacurium at the laryngeal adductor muscles and the adductor po llicis. Methods: In 22 adults, anesthesia was induced and maintained w ith propofol and alfentanil. The force of contraction of the adductor pollicis was recorded, and the laryngeal response was evaluated by mea suring the pressure change in the cuff of a tracheal tube positioned b etween the vocal cords after train-of-four stimulation. Mivacurium (0. 07 mg . kg(-1) or 0.14 mg . kg(-1)) was given intravenously (10 s). Re sults: With 0.07 mg kg(-1) mivacurium, onset time was 151 +/- 40 s (me an +/- SD) at the larynx and 241 +/- 79 s at the adductor pollicis, re spectively (P < 0.005). Maximum block was 78 +/- 18% and 95 +/- 8%, re spectively (P < 0.002), and time to 90% recovery was 11.1 +/- 2.9 min and 23.3 +/- 7.6 min, respectively (P < 0.001). With 0.14 mg . kg(-1) mivacurium, onset time also was more rapid at the vocal cords (137 +/- 20 s) than at the adductor pollicis (201 +/- 59 s, P +/- 0.01). Maxim um block was 90 +/- 7% and 99 +/- 1% (P < 0.005), and time to 90% reco very was 16.4 +/- 4.9 min and 27.4 +/- 7.8 min, respectively (P < 0.01 ). Conclusions: With mivacurium, onset and recovery are faster at the laryngeal muscles, but block is less intense than at the adductor poll icis. A dose greater than 0.14 mg . kg(-1) mivacurium is necessary to ensure complete relaxation at the vocal cords.