The onset of rocuronium, but not of vecuronium or mivacurium, is modified by tourniquet inflation.
A previous investigation showed that inflation of a tourniquet did not interrupt onset of vecuronium neuromuscular block. To test the hypothesis that this effect depended on potency, twitch tension was measured in an arm with a tourniquet inflated during onset and compared with a control arm in 30 patients under fentanyl-thiopental-nitrous oxide-isoflurane anesthesia. Patients were randomly allocated to receive either vecuronium 0.1 mg/kg (n = 10), rocuronium 0.6 mg/kg (n = 10), or mivacurium 0.2 mg/kg (n = 10). The electromyographic response of the first dorsal interosseus to single twitch stimulation of the ulnar nerve every 10 s was recorded in both arms. When neuromuscular block was 20% (i.e., twitch tension was 80% of control), the tourniquet was inflated to a pressure of 300 mm Hg. It was deflated 5 min later. In the vecuronium and mivacurium groups, the tourniquet did not influence onset of block. In the rocuronium group, maximum neuromuscular block was (mean +/- SD) 79% +/- 10% in the tourniquet arm, compared with 96% +/- 4% in the perfused arm (P < 0.05). The maximum rate of onset was half that of the perfused arm. The difference in maximum neuromuscular block between arms was 17% +/- 7%, 5% +/- 5%, and 0% +/- 2% in the rocuronium, vecuronium, and mivacurium groups (P < 0.05). To explain that onset of block continues in spite of interruption of blood flow, drug molecules must gain access to the neuromuscular junction via routes other than the circulation. The results of this investigation are consistent with the hypothesis that there is redistribution of drug from extrajunctional to junctional areas during onset of action of muscle relaxants and this process is more important for the more potent drugs (vecuronium and mivacurium) than for rocuronium.
Audibert
G
G
Department of Anesthesia, Hôtel-Dieu Hospital, Montréal, Québec, Canada.
Donati
F
F
D000328:Adult; D000368:Aged; D000732:Androstanols / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007546:Isoquinolines / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D000077590:Mivacurium; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology*; D012039:Regional Blood Flow; D000077123:Rocuronium; D013997:Time Factors; D014111:Tourniquets; D014673:Vecuronium Bromide / Q000494:pharmacology*
D000732:Androstanols; D007546:Isoquinolines; D003473:Neuromuscular Nondepolarizing Agents; D000077590:Mivacurium; D014673:Vecuronium Bromide; D000077123:Rocuronium