Effects of an intubating dose of succinylcholine and rocuronium on the larynx and diaphragm - An electromyographic study in humans

Background: Paralysis of the vocal cords is one objective of using relaxant s to facilitate tracheal intubation, This study compares the neuromuscular blocking effect of succinylcholine and rocuronium on the larynx, the diaphr agm, and the adductor pollicis muscle. Methods: Electromyographic response was used to compare the neuromuscular b locking effect of succinylcholine and rocuronium on the laryngeal adductor muscles, the diaphragm, and the adductor pollicis muscle. Sixteen patients undergoing elective surgery were anesthetized with propofol and fentanyl, a nd their tracheas were intubated without neuromuscular blocking agents, The recurrent laryngeal and phrenic nerves were stimulated at the neck. The el ectromyographic response was recorded from electrodes placed on the endotra cheal tube and intercostally before and after administration of 1 mg/kg suc cinylcholine or 0.6 mg/kg rocuronium, Results: The maximum effect was greater at the adductor pollicis (100 and 9 9%) than at the larynx (96 and 97%) and the diaphragm (94 and 96%) after ad ministration of succinylcholine and rocuronium, respectively (P less than o r equal to 0.05), Onset time was not different between the larynx (58 +/- 1 0 s), the diaphragm (57 +/- 8 s), and the adductor pollicis (54 +/- 13 s), after succinylcholine (all mean +/- SD). After rocuronium, onset time was 1 24 +/- 39 s at the larynx, 130 +/- 44 s at the diaphragm, and 115 +/- 21 s at the adductor pollicis. After succinylcholine administration, time to 90% recovery was 8.3 +/- 3.2, 7.2 +/- 3.5, and 9.1 +/- 3.0 min at the larynx, the diaphragm, and the adductor pollicis, respectively. Time to 90% recover y after rocuronium administration was 34.9 +/- 7.6, 30.4 +/- 4.2, and 49.1 +/- 11.4 min at the larynx, the diaphragm, and the adductor pollicis, respe ctively, Conclusion: Neuromuscular blocking effect of muscle relaxants on the larynx can be measured noninvasively by electromyography. Although the larynx app ears to be resistant to muscle relaxants, we could not demonstrate that its onset time differed from that of peripheral muscles.