The Effect of Adding Two Different Doses of Magnesium Sulphate as Adjuvant to Ropivacaine in Peribulbar Block for Cataract Surgery

Abstract

Background: This study was designed to compare the effects of adding two different doses of magnesium sulphate to the local anesthesia during peribulbar block. Patients and methods: The study comprised 105 patients undergoing cataract surgeries. The patients were divided randomly into three groups (35 patients in each group): Group I (Control group): patients received peribulbar anesthesia using a mixture of 6 ml of 0.5% ropivacaine, 1 ml (150 IU) hyaluronidase and 1 ml of normal saline, Group II (Mg 50): patients received peribulbar anesthesia using a mixture of 6 ml of 0.5% ropivacaine, 1 ml (150 IU) hyaluronidase and 50 mg of magnesium sulphate in 1 ml saline and Group III (Mg 100): patients received peribulbar anesthesia using a mixture of 6 ml of 0.5% ropivacaine, 1 ml (150 IU) hyaluronidase and 1 ml of 100 mg magnesium sulphate. Corneal sensation and motor block were evaluated, total amount of local anesthetic, duration sensory and motor block were assessed, analgesia was assessed by using visual analogue score (VAS) at the end of surgery, 1 h, 2 h, 4 h and 6 h. Statistical analysis was done using ANOVA test, Kruskal Wallis test And Chi-square test (χ2) to study association between qualitative variables. Whenever any of the expected cells were less than five, Fischer’s Exact test with Yates correction was used. P- value of <0.05 was considered statistically significant. Results: Patients received magnesium sulphate showed significantly rapid onset of lid and globe akinesia (P<0.0001) and significantly prolonged duration of akinesia than the control (P<0.0001). First analgesic requirement is significantly delayed in group II and group III comparison with the control group (group I) (P<0.0001). There were statistically significant differences between the three groups as regard the mean VAS in 4 and 6 hours, group II and group III have lower median pain score than group I (control group) (P<0.0001). Conclusion: Addition of 50 mg or 100 mg of magnesium sulfate to ropivacaine in peribulbar block led to rapid onset and prolonged the duration of sensory and motor blockade without adverse effects with reduction of the postoperative analgesic requirements. The results were more significant on using 100 mg magnesium sulfate.