title: The effects of age, isoflurane and sevoflurane on atracurium in lambs.
abstract: OBJECTIVE
  To determine the effects of age, sevoflurane and isoflurane on atracurium-induced neuromuscular blockade in 3-16 week-old lambs.
  
  
  METHODS
  Prospective randomized experimental trial.
  
  
  METHODS
  Twenty-six Scottish blackface ewe-lambs were anaesthetized for spinal surgery when either 3-6 (mean age 4.6 weeks; n = 18) or 12-16 weeks (mean age 13.7 weeks; n = 15) of age; seven animals were anaesthetized at both ages.
  
  
  METHODS
  After intramuscular injection of medetomidine (10 μg kg(-1)) anaesthesia was induced in the younger lambs either with isoflurane or sevoflurane in oxygen delivered by mask, and in the older lambs with ketamine (4 mg kg(-1)), and midazolam (0.2 mg kg(-1) ) administered intravenously (IV). In both groups anaesthesia was maintained with fixed end-tidal concentrations of either sevoflurane (2.8%) or isoflurane (1.8%) delivered in oxygen. Before surgery meloxicam (0.6 mg kg(-1)), morphine (0.5 mg kg(-1)) and ketamine (1 mg kg(-1) followed by 10 μg kg(-1) minute(-1) ) were administered IV. The lungs were ventilated mechanically to maintain normocapnia. Neuromuscular block was achieved with a loading dose (LD) of atracurium (0.5 mg kg(-1) IV). The peroneal nerve was stimulated (train-of-four every 12 seconds). Evoked responses in the digital extensor muscles were evaluated by palpation and observation. Maintenance doses (MD) of atracurium (0.17 mg kg(-1) IV) were administered when the first twitch (T1) returned. The onset and duration of LD action (T1 absent) and the duration of MD were recorded. Data were analysed using Student's t test, Mann-Whitney U test, repeated-measures anova, Wilcoxon's matched pairs test or Pearson correlation coefficient as relevant (p < 0.05).
  
  
  RESULTS
  Onset of LD action developed significantly (p < 0.05) more rapidly in isoflurane compared with sevoflurane-anaesthetized lambs (55 ± 18 cf. 80 ± 37 seconds). Duration of action of LDs and MDs was longer (p < 0.05) in lambs aged 12-16 than 3-6 weeks (33 ± 5.4 cf. 25 ± 6.4 and 26 ± 4.2 cf. 18 ± 5.5 minutes) but were independent of the anaesthetic used.
  
  
  CONCLUSIONS
  The effect of atracurium is age-dependent in lambs being prolonged in older animals. The onset of neuromuscular blockade is more rapid in isoflurane compared with sevoflurane-anaesthetized lambs.
authors.affiliation: Division of Veterinary Clinical Sciences, Royal (Dick) School of Veterinary Studies, Easter Bush Veterinary Centre, The University of Edinburgh, Roslin, Midlothian, UK. gudrun.schoeffmann@vetmeduni.ac.at
authors.forename: Gudrun
authors.initials: G
authors.lastname: Schöffmann
authors.forename: Enzo
authors.initials: E
authors.lastname: Vettorato
authors.forename: John G
authors.initials: JG
authors.lastname: Burke
authors.forename: Alastair J N
authors.initials: AJ
authors.lastname: Gibson
authors.forename: Eddie R
authors.initials: ER
authors.lastname: Clutton
mesh_terms: D000375:Aging / Q000502:physiology*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001279:Atracurium / Q000008:administration & dosage / Q000494:pharmacology*; D001831:Body Temperature; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005260:Female; D007530:Isoflurane / Q000008:administration & dosage / Q000494:pharmacology*; D008738:Methyl Ethers / Q000008:administration & dosage / Q000494:pharmacology*; D003473:Neuromuscular Nondepolarizing Agents / Q000008:administration & dosage / Q000494:pharmacology; D000077149:Sevoflurane; D012756:Sheep / Q000502:physiology*
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D003473:Neuromuscular Nondepolarizing Agents; D001279:Atracurium; D000077149:Sevoflurane; D007530:Isoflurane