title: Observations on the muscle relaxant rocuronium bromide in the horse--a dose-response study.
abstract: OBJECTIVE
  To investigate the onset and duration of neuromuscular blockade of rocuronium bromide and its associated haemodynamic effects at three doses in healthy horses.
  
  
  METHODS
  Prospective, randomized experimental study.
  
  
  METHODS
  Seven adult horses aged 3-20 (mean 10.3) years and weighing 466 +/- 44 (mean +/- SD) kg.
  
  
  METHODS
  Horses were anaesthetized three times with at least 2 weeks between. They were pre-medicated with 0.6 mg kg(-1) xylazine and 0.01 mg kg(-1) butorphanol i.v.. Anaesthesia was induced with 2.2 mg kg(-1) ketamine and 0.1 mg kg(-1) diazepam i.v.. Following orotracheal intubation anaesthesia was maintained with isoflurane in 100% oxygen. Intermittent positive pressure ventilation was initiated and the horses were ventilated at a respiratory rate (fr) of 4-8 breaths minute(-1). Neuromuscular function was monitored with an acceleromyograph. The peroneal nerve was stimulated with train-of-four (TOF) mode at 2 Hz every 15 seconds. Each horse received, in randomly assigned order, one of the three doses of rocuronium: 0.2 mg kg(-1) (D02), 0.4 mg kg(-1) (D04) or 0.6 mg kg(-1) (D06) i.v.. Lag time, onset time, time of no response, duration of action and the TOF ratio 0.7 and 0.9 were measured. Recovery time (T1(25-75)) was calculated. Vital parameters were recorded at 5-minute intervals on a standard anaesthetic record form.
  
  
  RESULTS
  Rocuronium produced a dose-dependent duration of action in isoflurane-anaesthetized horses. 100% block was observed in D04 and D06 but not in D02, in which the maximum decrease of the first twitch of TOF attained was 91.5 +/- 16.5%. Time to T1(25) was 13.1 +/- 5.5 minutes, 38.6 +/- 10.1 minutes and 55 +/- 9.8 minutes in D02, D04 and D06 respectively. There was a significantly shorter time for TOFR 0.9 with 0.2 mg kg(-1) compared with 0.4 and 0.6 mg kg(-1) rocuronium. T1(25-75) in D04 and D6 was not statistically significantly different. Heart rate, systolic, diastolic and mean arterial blood pressure increased slightly during the observation period.
  
  
  CONCLUSIONS
  Rocuronium is an effective nondepolarizing muscle relaxant in horses under isoflurane anaesthesia. It had a dose-dependent onset and duration of action. Rocuronium did not produce significant changes in the measured cardiovascular parameters.
authors.affiliation: Clinic of Anaesthesiology and Perioperative Intensive Care, University of Veterinary Medicine Vienna, Vienna, Austria. ulrike.auer@vu-wien.ac.at
authors.forename: Ulrike
authors.initials: U
authors.lastname: Auer
authors.forename: Carmen
authors.initials: C
authors.lastname: Uray
authors.forename: Martina
authors.initials: M
authors.lastname: Mosing
mesh_terms: D000732:Androstanols / Q000008:administration & dosage*; D000768:Anesthesia, General / Q000662:veterinary*; D018685:Anesthetics, Inhalation; D000818:Animals; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects; D006736:Horses / Q000502:physiology*; D007262:Infusions, Intravenous; D007530:Isoflurane / Q000008:administration & dosage; D019148:Neuromuscular Blockade / Q000662:veterinary; D003473:Neuromuscular Nondepolarizing Agents / Q000008:administration & dosage*; D011446:Prospective Studies; D000077123:Rocuronium
chemical_list: D000732:Androstanols; D018685:Anesthetics, Inhalation; D003473:Neuromuscular Nondepolarizing Agents; D007530:Isoflurane; D000077123:Rocuronium