Isoflurane Concentration when Compared with Intramuscular Morphine during Patellar Luxation Repair in Dogs

Abstract

This clinical trial aimed to assess the intraoperative analgesic effect, based on the required minimum alveolarconcentration (MAC) of isoflurane, of transdermal fentanyl when compared with intramuscular morphine in dogsundergoing patellar luxation repair. Seventeen healthy dogs with grade II or grade III of medial patellar luxationwere randomly assigned to group M or group F, receiving a sham patch or a transdermal fentanyl patch (25 μg/h),respectively, applied on the skin at least 24 h prior to surgery. Three dogs had bilateral medial patellar luxation andwere then enrolled in both groups, resulting in ten animals for each group. Before surgery, group M dogs werepremedicated intramuscularly with 0.03 mg/kg acepromazine and 0.5 mg/kg morphine while group F dogs werepremedicated intramuscularly with the same dose of acepromazine and normal saline at an equivalent volume tomorphine. Anesthesia was induced intravenously with propofol and maintained with isoflurane in oxygen andassisted respiration. Anesthesia monitoring and measurement of all parameters in all dogs were conducted by thesame investigator blinded to the applied patches and premedications. Vital signs, end-tidal concentration and MACof isoflurane were monitored and recorded before making surgical incision (baseline values) and at 5-min intervalsafter initiation of the incision (intraoperative values). All patellar luxation were repaired by the same surgeon andtechniques. Mean±SD (median) baseline and intraoperative MACs of isoflurane for group M were 1.22±0.25% (1.2%)and 1.1±0.27% (1.1%), respectively; and for group F were 1.1±0.31% (1.05%) and 1.1±0.26% (1%), respectively.Significant differences between the baseline and intraoprative isoflurane MACs within each group and between thetwo groups were not observed (p>0.05); indicating that transdermal fentanyl and intramuscular morphine havecomparable intraoperative analgesic effects. In conclusion, transdermal fentanyl patches can be used for preemptiveanalgesia to reduce the required isoflurane concentration during surgery.