Comparison of the preemptive analgesia of low dose ketamine versus magnesium sulfate on parturient undergoing cesarean section under general anesthesia

Objective
To investigate the efficacy of the preemptive analgesic effect of low dose ketamine versus MgSO on potentiating postoperative analgesia when compared to placebo in patients undergoing cesarean section under general anesthesia.
Methods
This prospective randomized blind study included 60 parturient females scheduled for cesarean section under general anesthesia. They were randomized into three equal groups [20 ]: group I []: received 20 ml normal saline 0.9%, group II []: received ketamine 0.3 mg/kg in 20 ml normal saline and group III [MgSO]: received MgSO, 30 mg/kg in 20 ml normal saline. Investigated medications infused over 10 min before induction of anesthesia. Fentanyl requirement, mean BP and HR were measured intraoperatively. Pain, sedation and nausea and vomiting were assessed at 2, 6, 12 and 24 h postoperatively. Total postoperative pethidine dose over 24 h was calculated.
Results
MBP and HR showed statistically significantly lower value in group (K) and (M) compared to group (C) at postintubation and postincision readings. Intraoperative fentanyl requirement was statistically higher in (C) groups compared to (K) and (M) groups. The time for first request for postoperative analgesia was longer and the total postoperative pethidine dose over 24 h was lower in (K) group compared to (C) and (M) groups. Postoperative VAS scores at 2 and 6 h postoperatively showed statistically highly significantly lower values in (K) group compared to (C) and (M) groups. Apgar, postoperative sedation and PONV scores showed no statistically significant differences among the three groups.
Conclusions
Preemptive dose of either ketamine (0.3 mg/kg) or MgSO (30 mg/kg) in patients undergoing cesarean section under general anesthesia could suppress the pressor response to endotracheal intubation and skin incision and decreased the intraoperative fentanyl requirement. Ketamine showed a significant preemptive analgesic effect compared to MgSO at 2 and 6 h postoperatively.