Clonidine combined with a long acting local anesthetic does not prolong postoperative analgesia after brachial plexus block but does induce hemodynamic changes

Clonidine in brachial plexus block prolongs analgesia of local anesthetics of short and intermediate duration. We performed a prospective randomized d ouble-blinded study to determine the efficacy and adverse effects of clonid ine mixed with a long-acting local anesthetic on postoperative analgesia. S ixty adult patients underwent elective rotator cuff repair using interscale ne brachial plexus block combined with general anesthesia and were randomly divided into one of the following three groups. Placebo (n = 20): intersca lene block with 40 mt of 0.5% bupivacaine with epinephrine (1/200000) and 1 mt of 0.9% saline, completed by 1 mt of 0.9% saline IM in the controlatera l shoulder; Control (n = 20): interscalene block with 40 mt of 0.5% bupivac aine with epinephrine and 1 mt of 0.9% saline, completed by 150 mug (=1 mt) of clonidine IM; Clonidine (n = 20): interscalene block with 40 mt of 0.5% bupivacaine with epinephrine and 150 mug (=1 mL) of clonidine, completed b y 1 mt of 0.9% saline IM. During anesthesia hemodynamic variables and fract ional expired isoflurane concentration (FeISO) were recorded. The following postoperative variables were assessed: duration of interscalene block, qua lity of pain relief on a visual analog scale, side effects, and consumption of morphine with a patient-controlled analgesia device over 48 h. Patient characteristics were comparable. During anesthesia mean arterial pressure, heart Fate, and FeISO were significantly decreased in Clonidine and Control groups compared with Placebo group. Duration of analgesia, defined as the time elapsed from interscalene injection to the first morphine request, was 983 +/- 489 min in the Placebo, 909 +/- 160 min in the Control, and 829 +/ - 159 min in the Clonidine groups. Pain scores and consumption of morphine at 24 h and 48 h showed no differences among the three groups. We conclude that adding 150 mug of clonidine in interscalene block does not prolong ana lgesia induced by 40 mt of bupivacaine 0.5% with epinephrine, but decreases mean arterial blood pressure and heart rate.