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Effects of transdermal fentanyl solution application and subsequent naloxone hydrochloride administration on minimum alveolar concentration of isoflurane in dogs

Grasso, Stefania C., Ko, Jeff C., Weil, Ann B., Hess, Jennifer A., Paranjape, Vaidehi, Payton, Mark
Journal of the American Veterinary Medical Association 2018 v.253 no.4 pp. 431-436
blood pressure, carbon dioxide, dogs, fentanyl, heart rate, isoflurane, mixed breeds, naloxone, oxygen, respiratory rate, sodium chloride, tail
OBJECTIVE To assess the isoflurane-sparing effect of a transdermal formulation of fentanyl solution (TFS) and subsequent naloxone administration in dogs. DESIGN Experiment. ANIMALS 6 healthy mixed-breed dogs. PROCEDURES Minimum alveolar concentration (MAC) of isoflurane was determined in each dog with a tail clamp method (baseline). Two weeks later, dogs were treated with TFS (2.7 mg/kg [1.23 mg/lb]), and the MAC of isoflurane was determined 4 and 24 hours later. After the 4-hour MAC assessment, saline (0.9% NaCl) solution was immediately administered IV and MAC was reassessed. After the 24-hour MAC assessment, naloxone hydrochloride (0.02 mg/kg [0.01 mg/lb], IV) was immediately administered and MAC was reassessed. Heart rate, respiratory rate, arterial blood pressure, end-tidal partial pressure of CO2, and oxygen saturation as measured by pulse oximetry were recorded for each MAC assessment. RESULTS Mean ± SD MAC of isoflurane at 4 and 24 hours after TFS application was 45.4 ± 4.0% and 45.5 ± 4.5% lower than at baseline, respectively. Following naloxone administration, only a minimal reduction in MAC was identified (mean percentage decrease from baseline of 13.1 ± 2.2%, compared with 43.8 ± 5.6% for saline solution). Mean heart rate was significantly higher after naloxone administration (113.2 ± 22.2 beats/min) than after saline solution administration (76.7 ± 20.0 beats/min). No significant differences in other variables were identified among treatments. CONCLUSIONS AND CLINICAL RELEVANCE The isoflurane-sparing effects of TFS in healthy dogs were consistent and sustained between 4 and 24 hours after application, and these effects should be taken into consideration when anesthetizing or reanesthetizing TFS-treated dogs.