Effects of vecuronium and rocuronium in antagonistic laryngeal muscles and the anterior tibial muscle in the cat.
BACKGROUND
Adequate vocal cord paralysis and full recovery of laryngeal muscle function are important when muscle relaxants are used perioperatively. This study was designed to compare the effects of vecuronium and rocuronium at the vocal cord abductor and adductor muscles and the anterior tibial muscle in cats.


METHODS
Twelve adult cats were studied under pentobarbitone-N2O/O2-anesthesia. After supramaximal electrical stimulation of the peroneal nerve and the recurrent laryngeal nerve (0.1 Hz and intermittent train-of-four) evoked electromyographic responses were obtained from the anterior tibial muscle, the posterior cricoarytenoid muscle (vocal cord abductor) and two vocal cord adductor muscles, the lateral cricoarytenoid and the vocal muscle. Six cats received bolus doses of increasing size of vecuronium (ED90 22.5 microg x kg(-1)) and six cats rocuronium (ED90 90 microg x kg(-1)).


RESULTS
Equipotent doses of vecuronium and rocuronium caused a similar degree of paralysis in all muscles (vecuronium ED90: 70% blockade at the posterior cricoarytenoid, 83% at the lateral cricoarytenoid, 84% at the vocal muscle and 90% at the anterior tibial muscle; rocuronium ED90: 71% at the posterior cricoarytenoid, 67% at the lateral cricoarytenoid, 78% at the vocal muscle and 90% at the anterior tibial muscle; vecuronium 2 x ED90: 93% blockade at the posterior cricoarytenoid, 95% at the lateral cricoarytenoid, 97% at the vocal muscle and 99% at the anterior tibial muscle; rocuronium 2 x ED90: 89% blockade at the posterior and lateral cricoarytenoid, 93% at the vocal muscle and 100% at the anterior tibial muscle). Onset time was significantly shorter at the posterior cricoarytenoid muscle (290 s) compared to the lateral cricoarytenoid muscle (400 s) after vecuronium ED90 and to the vocal muscle (150 s versus 210 s) after rocuronium ED90. Compared to the anterior tibial muscle (interval 25-75%: 6.5 min after vecuronium 2 x ED90 and 3.3 min after rocuronium 2 x ED90 and to the posterior cricoarytenoid muscle (interval 25-75%: 7 min after vecuronium 2 x ED90 and 4.3 min after rocuronium 2 x ED90), recovery of laryngeal adductor muscle function was markedly delayed with both neuromuscular blocking drugs (interval 25-75% at the lateral cricoarytenoid and vocal muscle: 14 min and 15.8 min after vecuronium 2 x ED90 and 10.3 min and 11.6 min after rocuronium 2 x ED90 respectively).


CONCLUSIONS
In cats, the time course of neuromuscular blockade after vecuronium and rocuronium differs in antagonistic laryngeal muscles. The protective laryngeal function of glottis closure recovers later than vocal cord abduction after both vecuronium and rocuronium.
Michalek-Sauberer
A
A
Department of Anesthesiology and General Intensive Care (A), University of Vienna, Austria. andrea.michalek-sauberer@univie.ac.at
Gilly
H
H
Steinbereithner
K
K
Vizi
E S
ES
D000732:Androstanols / Q000494:pharmacology*; D000818:Animals; D002415:Cats; D004558:Electric Stimulation; D004576:Electromyography; D006614:Hindlimb; D007821:Laryngeal Muscles / Q000187:drug effects* / Q000294:innervation; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000294:innervation; D019148:Neuromuscular Blockade; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology*; D010543:Peroneal Nerve / Q000502:physiology; D012009:Recurrent Laryngeal Nerve / Q000502:physiology; D000077123:Rocuronium; D013997:Time Factors; D014673:Vecuronium Bromide / Q000494:pharmacology*; D014827:Vocal Cords / Q000187:drug effects
D000732:Androstanols; D003473:Neuromuscular Nondepolarizing Agents; D014673:Vecuronium Bromide; D000077123:Rocuronium