Effect of transdermally administered fentanyl on minimum alveolar concentration of isoflurane in normothermic and hypothermic dogs.
OBJECTIVE
To determine whether the minimum alveolar concentration (MAC) of isoflurane was altered by transdermal administration of fentanyl in normothermic and hypothermic dogs.


METHODS
Randomized complete block crossover design.


METHODS
6 mature healthy dogs.


METHODS
Dogs received each of 4 treatments in random order. Following induction of anesthesia, normothermia was maintained in dogs that were treated with a fentanyl patch (F-NORM) or sham patch (C-NORM), or hypothermia was maintained in dogs that were treated with a fentanyl patch (F-HYPO) or sham patch (C-HYPO). The appropriate patch was applied 24 hours prior to induction of anesthesia. Anesthesia was induced with isoflurane in oxygen; the dogs were intubated and mechanically ventilated. Target esophageal temperatures were maintained within 1 degrees C of baseline values (normothermia) or at 34.5 degrees C (94.1 degrees F; hypothermia) for 1 hour prior to starting MAC determinations. Supramaximal stimulation was achieved with an electrical stimulator attached to needle electrodes placed in the buccal mucosa of the lower jaw of the dog.


RESULTS
Mean MAC +/- SEM of isoflurane during C-NORM, C-HYPO, F-NORM, and F-HYPO treatments were 1.20 +/- 0.17, 0.89 +/- 0.18, 0.76 +/- 0.10, and 0.81 +/- 0.17, respectively. The mean MAC during C-NORM was significantly higher than values for the other treatments. There was no significant difference in mean MAC among the C-HYPO, F-NORM, and F-HYPO treatments.


CONCLUSIONS
Data suggest that transdermal administration of fentanyl significantly reduces isoflurane requirements in normothermic dogs. The isoflurane MAC-sparing effects of transdermal fentanyl are not apparent in hypothermic dogs.
Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
Diane
D
Wilson
Glenn R
GR
Pettifer
Giselle
G
Hosgood
D000279:Administration, Cutaneous; D000701:Analgesics, Opioid / Q000494:pharmacology*; D018685:Anesthetics, Inhalation / Q000493:pharmacokinetics* / Q000494:pharmacology; D000818:Animals; D001831:Body Temperature / Q000502:physiology; D018592:Cross-Over Studies; D004285:Dogs / Q000378:metabolism*; D005260:Female; D005283:Fentanyl / Q000494:pharmacology*; D007035:Hypothermia / Q000378:metabolism / Q000662:veterinary*; D007036:Hypothermia, Induced / Q000379:methods / Q000662:veterinary; D007530:Isoflurane / Q000493:pharmacokinetics* / Q000494:pharmacology; D008297:Male; D011446:Prospective Studies; D011650:Pulmonary Alveoli / Q000187:drug effects* / Q000378:metabolism; D013997:Time Factors
D000701:Analgesics, Opioid; D018685:Anesthetics, Inhalation; D007530:Isoflurane; D005283:Fentanyl