title: The influence of the duration of isoflurane anaesthesia on neuromuscular effects of mivacurium.
abstract: BACKGROUND
  The pharmacodynamic profile of muscle relaxants is usually changed by volatile anaesthetics. These changes seem to be time-dependent, even though few data are available to substantiate this.
  
  
  METHODS
  We studied neuromuscular effects of a single dose of mivacurium (0.2 mg.kg-1) during short and intermediate duration of isoflurane anaesthesia. Forty-five children 1-10 years of age were randomized to receive 1.5% end-tidal concentration of isoflurane in N2O/O2 for 10 or 30 min (groups Iso-10 and Iso-30, respectively) or to receive nitrous oxide in oxygen for 10 min (Group N2O) before 0.2 mg.kg-1 of mivacurium was given. Neuromuscular response was recorded by adductor pollicis electromyogram.
  
  
  RESULTS
  The onset time of mivacurium was shorter in Group Iso-30, 1.7 (1.0-2.3) min than in Group Iso-10, 2.3 (1.7-3.3) min or Group N2O, 2.3 (1.7-3.3) min (median with 10-90% percentiles) (P < 0.05). In Group Iso-30 the recovery time of the first EMG response was significantly longer than in groups Iso-10 and N2O (P < 0.0001). Groups Iso-10 and N2O did not differ from each other.
  
  
  CONCLUSIONS
  Our results indicate that the duration of a constant concentration of isoflurane anaesthesia influences significantly the pharmacodynamics of mivacurium. The duration of a volatile anaesthesia is critical when potentiation of NMB is evaluated or compared in neuromuscular studies.
authors.affiliation: Department of Anaesthesiology, Children's Hospital, University of Helsinki, Finland.
authors.forename: L
authors.initials: L
authors.lastname: Jalkanen
authors.forename: O A
authors.initials: OA
authors.lastname: Meretoja
mesh_terms: D000758:Anesthesia; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D002648:Child; D002675:Child, Preschool; D004576:Electromyography; D006801:Humans; D007223:Infant; D007530:Isoflurane / Q000494:pharmacology*; D007546:Isoquinolines / Q000494:pharmacology*; D000077590:Mivacurium; D019148:Neuromuscular Blockade; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology*; D009609:Nitrous Oxide / Q000494:pharmacology; D013997:Time Factors
chemical_list: D018685:Anesthetics, Inhalation; D007546:Isoquinolines; D003473:Neuromuscular Nondepolarizing Agents; D000077590:Mivacurium; D007530:Isoflurane; D009609:Nitrous Oxide