Fentanyl versus magnesium sulphate as adjuvant to peribulbar anesthesia in cataract surgery

Background and Objectives
Fentanyl or magnesium sulphate may improve the quality of peribulbar block. We compared the effects of adding either fentanyl or magnesium sulphate to peribulbar block in patients undergoing cataract surgery on the quality of globe akinesia.
Methods
90 adult patients undergoing cataract surgery were randomly allocated into three groups. Peribulbar block was performed by a mixture of 4 ml lidocaine 2%, 4 ml bupivacaine 0.5%, hyaluronidase 150 IU diluted in normal saline to a total volume of 10 ml in control group. 20 μg fentanyl and 50 mg magnesium sulphate (10%) were added to the same mixture in fentanyl and magnesium groups respectively. Onset and duration of lid and globe akinesia, adequate time to start surgery and duration of postoperative analgesia were recorded.
Results
Addition of fentanyl significantly enhanced the onset of lid (1.54 ± 0.43 min) and globe akinesia (2.19 ± 0.75 min) as well as adequate time to start surgery (6.23 ± 1.8 min) compared to both control (P < 0.05) and magnesium sulphate (P < 0.05) groups while the comparison between control and magnesium sulphate groups was statistically insignificant (P > 0.05). Time of first analgesic request was significantly prolonged in both fentanyl and magnesium sulphate groups compared to the control group (P < 0.05).
Conclusions
Addition of fentanyl (2 μg/ml) or magnesium sulphate (50 mg) to peribulbar block in patients undergoing cataract surgery equally prolongs the duration of postoperative analgesia. In addition to this effect, fentanyl fastens the onset lid and globe akinesia and provides better akinesia score.