title: A clinical study on the effect in horses during medetomidine-isoflurane anaesthesia, of butorphanol constant rate infusion on isoflurane requirements, on cardiopulmonary function and on recovery characteristics.
abstract: OBJECTIVE
  To test if the addition of butorphanol by constant rate infusion (CRI) to medetomidine-isoflurane anaesthesia reduced isoflurane requirements, and influenced cardiopulmonary function and/or recovery characteristics.
  
  
  METHODS
  Prospective blinded randomised clinical trial.
  
  
  METHODS
  61 horses undergoing elective surgery.
  
  
  METHODS
  Horses were sedated with intravenous (i.v.) medetomidine (7 μg kg(-1)); anaesthesia was induced with i.v. ketamine (2.2 mg kg(-1)) and diazepam (0.02 mg kg(-1)) and maintained with isoflurane and a CRI of medetomidine (3.5 μg kg(-1) hour(-1)). Group MB (n = 31) received butorphanol CRI (25 μg kg(-1) i.v. bolus then 25 μg kg(-1) hour(-1)); Group M (n = 30) an equal volume of saline. Artificial ventilation maintained end-tidal CO2 in the normal range. Horses received lactated Ringer's solution 5 mL kg(-1) hour(-1), dobutamine <1.25 μg kg(-1) minute(-1) and colloids if required. Inspired and exhaled gases, heart rate and mean arterial blood pressure (MAP) were monitored continuously; pH and arterial blood gases were measured every 30 minutes. Recovery was timed and scored. Data were analyzed using two way repeated measures anova, independent t-tests or Mann-Whitney Rank Sum test (p < 0.05).
  
  
  RESULTS
  There was no difference between groups with respect to anaesthesia duration, end-tidal isoflurane (MB: mean 1.06 ± SD 0.11, M: 1.05 ± 0.1%), MAP (MB: 88 ± 9, M: 87 ± 7 mmHg), heart rate (MB: 33 ± 6, M: 35 ± 8 beats minute(-1)), pH, PaO2 (MB: 19.2 ± 6.6, M: 18.2 ± 6.6 kPa) or PaCO2. Recovery times and quality did not differ between groups, but the time to extubation was significantly longer in group MB (26.9 ± 10.9 minutes) than in group M (20.4 ± 9.4 minutes).
  
  
  CONCLUSIONS
  Butorphanol CRI at the dose used does not decrease isoflurane requirements in horses anaesthetised with medetomidine-isoflurane and has no influence on cardiopulmonary function or recovery.
authors.affiliation: Section of Anaesthesiology, Equine Department, Vetsuisse Faculty University of Zurich, Zurich, Switzerland. rbettschart@vetclinics.uzh.ch
authors.forename: Regula
authors.initials: R
authors.lastname: Bettschart-Wolfensberger
authors.forename: Sidonia
authors.initials: S
authors.lastname: Dicht
authors.forename: Cecilia
authors.initials: C
authors.lastname: Vullo
authors.forename: Angela
authors.initials: A
authors.lastname: Frotzler
authors.forename: Jan M
authors.initials: JM
authors.lastname: Kuemmerle
authors.forename: Simone K
authors.initials: SK
authors.lastname: Ringer
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D000758:Anesthesia / Q000662:veterinary*; D000762:Anesthesia Recovery Period; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary; D001794:Blood Pressure / Q000187:drug effects; D002077:Butorphanol / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004562:Electrocardiography / Q000187:drug effects / Q000662:veterinary; D006736:Horses / Q000601:surgery*; D006993:Hypnotics and Sedatives / Q000008:administration & dosage; D007263:Infusions, Parenteral / Q000662:veterinary; D007530:Isoflurane / Q000008:administration & dosage*; D020926:Medetomidine / Q000008:administration & dosage; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange / Q000187:drug effects; D016037:Single-Blind Method
chemical_list: D000701:Analgesics, Opioid; D018685:Anesthetics, Inhalation; D006993:Hypnotics and Sedatives; D007530:Isoflurane; D020926:Medetomidine; D002077:Butorphanol