dose response study of three different concentrations of clonidine with local anesthetic mixture for peribulbar block

Clonidine, the alpha[2] agonist prolong anesthesia and analgesia when added to local anesthetics, in epidural anesthesia, subarachnoid anesthesia, plexus anesthesia and retrobulbar block. We evaluate the dose-response relationship of different concentrations of clonidine added to lidocaine in peribulbar block. Sixty patients undergoing cataract surgery were given peribulbar block with 7-10 ml of 2% lidocaine and hyaluronidase with either saline [control] or clonidine 0.5 ug/kg [0.5 clon] 1.0 ug/ kg [1.0 clon] or 1.5 ug/kg [1.5 clon] doses. The onset of globe anesthesia, akinesia and analgesia, the duration of anesthesia and analgesia, the postoperative analgesia requirement and the adverse effects [Hypotension, bradycardia, hypoxia, sedation and dizziness] were recorded. The onset of block was comparable in all groups. The duration of globe anesthesia, analgesia and akinesia was significantly [p<0.01] prolonged in patients receiving 1.0 and 1.5 ug/kg clonidine as compared with the control group. Perioperative pain scores and analgesic requirements were significantly less in these groups. 0.5 ug/kg clonidine did not significantly increase the duration of anesthesia and analgesia. The side effects were observed more with 1.5 ug/kg clonidine as compared with other groups. We conclude that 1.0 ug/kg clonidine significantly prolong the anesthesia and analgesia when mixed with local anesthetic with minimal side effects