title: Effect of lidocaine on the minimum alveolar concentration of isoflurane in dogs.
abstract: OBJECTIVE
  To determine the influence of a low-dose constant rate infusion (LCRI; 50 microg kg(-1) minute(-1)) and high-dose CRI (HCRI; 200 microg kg(-1) minute(-1)) lidocaine infusion on the minimum alveolar concentration (MAC) of isoflurane (I) in dogs.
  
  
  METHODS
  Prospective experimental study.
  
  
  METHODS
  Ten mongrel dogs (four females, six males), weighing 20-26.3 kg.
  
  
  METHODS
  Dogs were anesthetized with I in oxygen and their lungs mechanically ventilated. Baseline MAC was determined using mechanical or electrical stimuli. Lidocaine (2 mg kg(-1) IV) was administered over 3 minutes, followed by the LCRI and MAC determination commenced 30 minutes later. Once MAC was determined following LCRI, the lidocaine infusion was stopped for 30 minutes. A second bolus of lidocaine (2 mg kg(-1), IV) was administered, followed by the HCRI and MAC re-determined. Concentrations of lidocaine and its metabolites were measured at end-tidal I concentrations immediately above and below MAC. Heart rates and blood pressures were measured.
  
  
  RESULTS
  Minimum alveolar concentration of I was 1.34 +/- 0.11 (%; mean +/- SD) for both types of stimulus. The LCRI significantly reduced MAC to 1.09 +/- 0.13 (18.7% reduction) and HCRI to 0.76 +/- 0.10 (43.3% reduction). Plasma concentrations (ng mL(-1), median; value below and above MAC, respectively) for LCRI were: lidocaine, 1465 and 1537; glycinexylidide (GX), 111 and 181; monoethylglycinexylidide (MEGX), 180 and 471 and for HCRI were: lidocaine, 4350 and 4691; GX, 784 and 862; MEGX, 714 and 710. Blood pressure was significantly increased at 30 minutes after high dose infusion.
  
  
  CONCLUSIONS
  Lidocaine infusions reduced the MAC of I in a dose-dependent manner and did not induce clinically significant changes on heart rate or blood pressure.
authors.affiliation: Department of Large Animal Clinical Sciences, University of Florida, Gainesville, FL 32610, USA. valverdea@mail.vetmed.ufl.edu
authors.forename: Alexander
authors.initials: A
authors.lastname: Valverde
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Doherty
authors.forename: Jorge
authors.initials: J
authors.lastname: Hernández
authors.forename: Wendy
authors.initials: W
authors.lastname: Davies
mesh_terms: D018685:Anesthetics, Inhalation / Q000493:pharmacokinetics*; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure; D004285:Dogs / Q000378:metabolism*; D005260:Female; D006339:Heart Rate; D007262:Infusions, Intravenous / Q000662:veterinary; D007530:Isoflurane / Q000493:pharmacokinetics*; D008012:Lidocaine / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D011446:Prospective Studies; D011650:Pulmonary Alveoli / Q000378:metabolism*
chemical_list: D018685:Anesthetics, Inhalation; D000779:Anesthetics, Local; D008012:Lidocaine; D007530:Isoflurane