Fentanyl supplement expedites the onset time of sensory and motor blocking in interscalene lidocaine anesthesia

Background and the purpose of the study: Opioids are usually used in regional anesthesia, with or without local anesthetics to improve the regional block or postoperative pain control. Since no data are available on fentanyl's effect on the onset time of lidocaine interscalene anesthesia, the purpose of this study was to examine its effect on the onset time of sensory and motor blockade during interscalene anesthesia. In a prospective, randomized, double-blind study, ninety patients scheduled for elective shoulder, arm and forearm surgeries under an interscalene brachial plexus block. They were randomly allocated to receive either 30 ml of 1.5 % lidocaine with 1.5 ml of isotonic saline (control group, n = 39) or 30 ml of 1.5% lidocaine with 1.5 ml (75µg) of fentanyl (fentanyl group,n=41). Then the onset time of sensory and motor blockades of the shoulder, arm and forearm were evaluated every 60 sec. The onset time of the sensory and motor blockades was defined as the time between the last injection and the total abolition of the pinprick response and complete paralysis. The duration of sensory blocks were considered as the time interval between the administration of the local anesthetic and the first postoperative pain sensation. Ten patients were excluded because of unsuccessful blockade or unbearable pain during the surgery. The onset time of the sensory block was significantly faster in the fentanyl group (186.54± 62.71sec) compared with the control group (289.51± 81.22, P < 0.01). The onset times of the motor block up to complete paralysis in forearm flexion was significantly faster in the fentanyl group (260.61± 119.91sec) than the control group (367.08± 162.43sec, P < 0.01) There was no difference in the duration of the sensory block between two groups. Results of the study showed that the combination of 75 µg fentanyl and 1.5% lidocaine solution accelerated the onset of sensory and motor blockade during interscalene anesthesia.