title: Effects of a constant rate infusion of magnesium sulphate in healthy dogs anaesthetized with isoflurane and undergoing ovariohysterectomy.
abstract: OBJECTIVE
  To determine the effects of intravenous (IV) magnesium sulphate (MgSO(4) ) as a bolus followed by a constant rate infusion (CRI) on anaesthetic requirements, neuroendocrine stress response to surgery, haemostasis and postoperative analgesia in healthy dogs undergoing ovariohysterectomy.
  
  
  METHODS
  Blinded randomized clinical trial.
  
  
  METHODS
  Sixteen female dogs.
  
  
  METHODS
  After intramuscular premedication with acepromazine (0.05 mg kg(-1) ) and morphine (0.3 mg kg(-1) ), anaesthesia was induced with diazepam (0.2 mg kg(-1) ) and propofol (2 mg kg(-1) ) intravenously and maintained with isoflurane in oxygen in all dogs. Dogs were randomly assigned to two groups, M and C. Group M received MgSO(4) (50 mg kg(-1) over 15 minutes, followed by a 15 mg kg(-1) hour(-1) CRI). Group C received an equivalent bolus and CRI of lactated Ringer's solution. In addition, all dogs received lactated Ringer's solution (10 mL kg(-1) over 15 minutes followed by 10 mL kg(-1) hour(-1) ). End-tidal isoflurane and carbon dioxide tensions, cardio-respiratory variables, arterial blood gases, electrolytes, ACTH and cortisol concentrations were measured at different time points. Thromboelastography (TEG) was performed pre- and post-anaesthesia. Postoperative pain was evaluated using the short form of the Glasgow Composite Pain Scale. Data were analysed with repeated measures anova and Mann-Whitney U tests (p < 0.05).
  
  
  RESULTS
  No statistically significant differences between groups were found in any of the measured variables. However, the alpha angle and maximal amplitude recorded by TEG in group M were significantly increased post-anaesthesia, but remained within the reference interval. One dog in Group M and two in Group C received rescue analgesia during recovery.
  
  
  CONCLUSIONS
  As used in this study, MgSO(4) failed to decrease isoflurane requirements, postoperative pain and stress hormone concentrations; however, it did not produce any cardio-respiratory or major haemostatic side effects. Administration of intravenous MgSO(4) together with an opioid during ovariohysterectomy in dogs does not seem to provide any clinical advantage.
authors.affiliation: Department of Companion Animal Clinical Studies, Faculty of Veterinary Sciences, University of Pretoria, South Africa. eva.riojagarcia@up.ac.za
authors.forename: Eva
authors.initials: E
authors.lastname: Rioja
authors.forename: Brighton T
authors.initials: BT
authors.lastname: Dzikiti
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Fosgate
authors.forename: Amelia
authors.initials: A
authors.lastname: Goddard
authors.forename: Frik G
authors.initials: FG
authors.lastname: Stegmann
authors.forename: Johan P
authors.initials: JP
authors.lastname: Schoeman
mesh_terms: D015667:Acupuncture Analgesia / Q000662:veterinary*; D000818:Animals; D004283:Dog Diseases / Q000517:prevention & control; D004285:Dogs; D005260:Female; D006487:Hemostasis / Q000187:drug effects; D007044:Hysterectomy / Q000662:veterinary*; D007275:Injections, Intravenous; D007530:Isoflurane / Q000494:pharmacology*; D008278:Magnesium Sulfate / Q000008:administration & dosage / Q000494:pharmacology*; D010052:Ovariectomy / Q000662:veterinary*; D010149:Postoperative Pain / Q000517:prevention & control / Q000662:veterinary; D013312:Stress, Physiological / Q000187:drug effects
chemical_list: D008278:Magnesium Sulfate; D007530:Isoflurane