title: Effects of constant rate infusion of lidocaine and ketamine, with or without morphine, on isoflurane MAC in horses.
abstract: BACKGROUND
  Lidocaine and ketamine are administered to horses as a constant rate infusion (CRI) during inhalation anaesthesia to reduce anaesthetic requirements. Morphine decreases the minimum alveolar concentration (MAC) in some domestic animals; when administered as a CRI in horses, morphine does not promote haemodynamic and ventilatory changes and exerts a positive effect on recovery. Isoflurane-sparing effect of lidocaine, ketamine and morphine coadministration has been evaluated in small animals but not in horses.
  
  
  OBJECTIVE
  To determine the reduction in isoflurane MAC produced by a CRI of lidocaine and ketamine, with or without morphine.
  
  
  OBJECTIVE
  Addition of morphine to a lidocaine-ketamine infusion reduces isoflurane requirement and morphine does not impair the anaesthetic recovery of horses.
  
  
  METHODS
  Six healthy adult horses were anaesthetised 3 times with xylazine (1.1 mg/kg bwt i.v.), ketamine (3 mg/kg bwt i.v.) and isoflurane and received a CRI of lidocaine-ketamine (LK), morphine-lidocaine-ketamine (MLK) or saline (CTL). The loading doses of morphine and lidocaine were 0.15 mg/kg bwt i.v and 2 mg/kg bwt i.v. followed by a CRI at 0.1 mg/kg bwt/h and 3 mg/kg bwt/h, respectively. Ketamine was given as a CRI at 3 mg/kg bwt/h. Changes in MAC characterised the anaesthetic-sparing effect of the drug infusions under study and quality of recovery was assessed using a scoring system.
  
  
  RESULTS
  Mean isoflurane MAC (mean ± s.d.) in the CTL, LK and MLK groups was 1.25 ± 0.14%, 0.64 ± 0.20% and 0.59 ± 0.14%, respectively, with MAC reduction in the LK and MLK groups being 49 and 53% (P<0.001), respectively. No significant differences were observed between groups in recovery from anaesthesia.
  
  
  CONCLUSIONS
  Administration of lidocaine and ketamine via CRI decreases isoflurane requirements. Coadministration of morphine does not provide further reduction in anaesthetic requirements and does not impair recovery.
authors.affiliation: Animal Medicine and Surgery Department, Veterinary Faculty, University Complutense, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Villalba
authors.forename: I
authors.initials: I
authors.lastname: Santiago
authors.forename: I A
authors.initials: IA
authors.lastname: Gomez de Segura
mesh_terms: D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology; D000762:Anesthesia Recovery Period; D000778:Anesthetics, Dissociative / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology; D000818:Animals; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D005260:Female; D006736:Horses; D007530:Isoflurane / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000494:pharmacology; D007649:Ketamine / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D008012:Lidocaine / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D011650:Pulmonary Alveoli / Q000378:metabolism
chemical_list: D000701:Analgesics, Opioid; D000778:Anesthetics, Dissociative; D018685:Anesthetics, Inhalation; D000779:Anesthetics, Local; D007649:Ketamine; D009020:Morphine; D008012:Lidocaine; D007530:Isoflurane