Evaluation of induction characteristics and hypnotic potency of isoflurane and sevoflurane in healthy dogs.
OBJECTIVE
To determine induction characteristics and the minimum alveolar concentration (MAC) at which consciousness returned (MACawake) in dogs anesthetized with isoflurane or sevoflurane.


METHODS
20 sexually intact male Beagles.


METHODS
In experiment 1, 20 dogs were randomly assigned to have anesthesia induced and maintained with isoflurane or sevoflurane. The MAC at which each dog awoke in response to auditory stimulation (MACawake-noise) was determined by decreasing the end-tidal concentration by 0.1 volume (vol %) every 15 minutes and delivering a standard audible stimulus at each concentration until the dog awoke. In experiment 2, 12 dogs received the same anesthetic agent they were administered in experiment 1. After duplicate MAC determination, the end-tidal concentration was continually decreased by 10% every 15 minutes until the dog awoke from anesthesia (MACawake).


RESULTS
Mean induction time was significantly greater for isoflurane-anesthetized dogs (212 seconds), compared with the sevoflurane-anesthetized dogs (154 seconds). Mean+/-SD MACawake-noise was 1.1+/-0.1 vol % for isoflurane and 2.0+/-0.2 vol % for sevoflurane. Mean MAC was 1.3+/-0.2 vol % for isoflurane and 2.1+/-0.6 vol % for sevoflurane, and mean MACawake was 1.0+/-0.1 vol % for isoflurane and 1.3+/-0.3 vol % for sevoflurane.


CONCLUSIONS
Sevoflurane resulted in a more rapid induction than did isoflurane. The MACawake for dogs was higher than values reported for both agents in humans. Care should be taken to ensure that dogs are at an appropriate anesthetic depth to prevent consciousness, particularly when single-agent inhalant anesthesia is used.
Hofmeister
Erik H
EH
Department of Small Animal Medicine and Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA 30602, USA.
Brainard
Benjamin M
BM
Sams
Lisa M
LM
Allman
David A
DA
Cruse
Ashley M
AM
D000762:Anesthesia Recovery Period; D000769:Anesthesia, Inhalation / Q000379:methods / Q000662:veterinary*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage* / Q000493:pharmacokinetics; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004285:Dogs / Q000378:metabolism / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects; D007530:Isoflurane / Q000008:administration & dosage* / Q000493:pharmacokinetics; D008297:Male; D008738:Methyl Ethers / Q000008:administration & dosage* / Q000493:pharmacokinetics; D012119:Respiration / Q000187:drug effects; D000077149:Sevoflurane; D018709:Statistics, Nonparametric
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D007530:Isoflurane