The effect of transdermal fentanyl patches on required isoflurane concentration when compared with intramuscular morphine during patellar luxation repair in dogs.

This clinical trial aimed to assess the intraoperative analgesic effect, based on the required minimum alveolar concentration (MAC) of isoflurane, of transdermal fentanyl when compared with intramuscular morphine in dogs undergoing patellar luxation repair. Seventeen healthy dogs with grade II or grade III of medial patellar luxation were randomly assigned to group M or group F, receiving a sham patch or a transdermal fentanyl patch (25 mu g/h), respectively, applied on the skin at least 24 h prior to surgery. Three dogs had bilateral medial patellar luxation and were then enrolled in both groups, resulting in ten animals for each group. Before surgery, group M dogs were premedicated intramuscularly with 0.03 mg/kg acepromazine and 0.5 mg/kg morphine while group F dogs were premedicated intramuscularly with the same dose of acepromazine and normal saline at an equivalent volume to morphine. Anesthesia was induced intravenously with propofol and maintained with isoflurane in oxygen and assisted respiration. Anesthesia monitoring and measurement of all parameters in all dogs were conducted by the same investigator blinded to the applied patches and premedications. Vital signs, end-tidal concentration and MAC of isoflurane were monitored and recorded before making surgical incision (baseline values) and at 5-min intervals after initiation of the incision (intraoperative values). All patellar luxation were repaired by the same surgeon and techniques. 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 the two groups were not observed (p>0.05); indicating that transdermal fentanyl and intramuscular morphine have comparable intraoperative analgesic effects. In conclusion, transdermal fentanyl patches can be used for preemptive analgesia to reduce the required isoflurane concentration during surgery.