Master of Science (MS)


Biomedical and Veterinary Medical Sciences - Veterinary Clinical Sciences

Document Type



Intraoperative reductions in serum fentanyl levels in dogs with induced moderate hypothermia and transdermal fentanyl patches (TDF) in place has been documented. The impact of such reductions has not been evaluated nor has the anesthetic sparing effect of the TDF. Reductions in serum levels may be the result of either a decreased uptake of fentanyl from the dermal depot, or a biophase shift. The objective of this investigation was to determine whether the minimum alveolar concentration (MAC) of isoflurane was altered in the presence of TDF in normothermic and hypothermic dogs. Six mature, healthy, mixed breed dogs were anesthetized on four separate occasions, and received each of the 4 following treatments in random order: 1. Sham patch-normothermia (C-NORM), 2. Sham patch-hypothermia (C-HYPO), 3. Fentanyl patch-normothermia (F-NORM), 4. Fentanyl hypothermia (F-HYPO). The appropriate patch was applied twenty four hours prior to induction of anesthesia. Anesthesia was induced with isoflurane in oxygen; the dogs were intubated and mechanical ventilation was initiated. Target temperatures (34.5ºC- HYPO, or within 1ºC of baseline- NORM) were held constant for one hour prior to beginning the MAC determinations. Supramaximal stimulation was produced by an electrical stimulator which delivered a current to needle electrodes in the buccal mucosa of the lower jaw of the dog. The MAC (± SD) for C-NORM, C-HYPO, F-NORM and F-HYPO was 1.2 ± 0.17, 0.855 ± 0.183, 0.763 ± 0.097, and 0.830 ± 0.172 respectively. MAC for C-NORM was significantly higher than the other groups. There was no significant difference between C-HYPO, F-NORM, and F-HYPO. Transdermal fentanyl reduces the isoflurane requirement in normothermic dogs. The presence of hypothermia appears to negate the effects of TDF.



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Committee Chair

Glenn Pettifer