INTRODUCTION: In this prospective, randomized, double-blind study, we evaluated the effect of an ultra-low dose of naloxone added to lidocaine and fentanyl mixture on the onset and duration of axillary brachial plexus block. METHODS: One hundred twelve patients scheduled for elective forearm surgery under axillary brachial plexus block were randomly allocated to receive 34 mL lidocaine 1.5% with 3 mL of isotonic saline chloride (control group, n = 28), 34 mL lidocaine 1.5% with 2 mL (100 microg) of fentanyl and 1 mL of isotonic saline chloride (fentanyl group, n = 28), 34 mL lidocaine 1.5% with 2 mL saline chloride and 100 ng (1 mL) naloxone (naloxone group, n = 28), or 34 mL lidocaine 1.5% with 2 mL (100 microg) of fentanyl and 100 ng (1 mL) naloxone (naloxone + fentanyl group, n = 28). A multiple stimulation technique was used in all patients. After performing the block, sensory and motor blockades of radial, median, musculocutaneous, and ulnar nerves were recorded at 5, 15, and 30 min. 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, respectively. The duration of sensory and motor blocks was considered as the time interval between the complete block and the first postoperative pain and complete recovery of motor functions. RESULTS: Sensory and motor onset times were longer in the naloxone (sensory onset time: 15 +/- 3, and motor onset time: 21 +/- 4) and naloxone + fentanyl group than control or fentanyl groups (sensory onset time: 10 +/- 3 min in control group, 10 +/- 4 min in fentanyl group, and 17 +/- 3 min in naloxone + fentanyl group, motor onset time: 15 +/- 5 min in control group, 14 +/- 7 min in fentanyl group, and 17.3 +/- 3.4 min in naloxone + fentanyl group) (P < 0.001). The duration of time to first postoperative pain and motor blockade was significantly longer in the naloxone (92 +/- 10 and 115 +/- 10 min) and naloxone + fentanyl groups (98 +/- 12 and 122 +/- 16 min) than control (68 +/- 7 and 89 +/- 11 min) and fentanyl groups (68 +/- 11 and 90 +/- 12 min) (P < 0.001). The time to first postoperative pain was significantly longer in the naloxone and naloxone + fentanyl groups than in the control or fentanyl groups (P < 0.001). CONCLUSIONS: The addition of an ultra-low dose of naloxone to lidocaine 1.5% solution with or without fentanyl solution in axillary brachial plexus block prolongs the time to first postoperative pain and motor blockade but also lengthens the onset time.
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