Evaluation of effect of intravenous Magnesium Sulfate infusion on tourniquet induced hypertension and pain in arthroscopic knee surgery patients under epidural anesthesia

Objective
This prospective randomized, double blind controlled study was designed to evaluate the effect of Intravenous (i.v) magnesium sulfate infusion on attenuation of tourniquet induced hypertension (TIH) and tourniquet pain and also its effect on postoperative analgesia in patients undergoing arthroscopic knee surgery under epidural anesthesia.
Patients and methods
Seventy ASA I and II patients were scheduled for arthroscopic knee surgery with tourniquet under epidural anesthesia. Patients were allocated randomly into two equal groups ( = 35): Magnesium (Mg group) received a bolus dose of IV magnesium sulfate 30 mg/kg in 50 ml saline over 10 min, followed by infusion 10 mg/kg/h and control group received iv saline. Systolic and Diastolic blood pressure (SBP, DBP) and Heart rate (HR) were measured at baseline (before anesthesia), after epidural anesthesia, then every 10 min after the tourniquet inflation, and 1, 5, 10, and 30 min after deflation with recording incidence of (TIH), tourniquet pain, and total iv fentanyl consumption (was given iv 1 ug/kg with tourniquet pain); postoperative Visual Analogue Scale (VAS) score was assessed at 1, 2, 4, 8, 12, 18, and 24 h, postoperative pethidine consumption (given iv 0.5 mg/kg if VAS > 3) was recorded, and serum magnesium was measured preoperatively and at 6 and 24 h postoperatively.
Results
SBP, DBP and HR were significantly higher in the control group than in the Mg group ( < 0.001) after 50 min of inflation. The number of patients who developed TIH and tourniquet pain was significantly lower in Mg group compared to control group 3(8.57%) vs 12(34.28%) ( < 0.05), with significantly shorter time to feel pain in control group 48 ± 8 min versus 71 ± 7 min ( < 0.001). Intraoperative fentanyl requirements were significantly higher in control group compared to Mg group ( < 0.001). Mg group had significantly lower postoperative VAS scores and pethidine consumption ( < 0.001) and significantly longer time to first request of postoperative analgesia compared to control group ( < 0.001). Postoperative serum magnesium was significantly higher in Mg group at 6 h postoperative ( < 0.001).
Conclusion
In patients undergoing arthroscopic knee surgery under epidural anesthesia, IV magnesium sulfate in a dose of 30 mg/kg, followed by 10 mg/kg/h infused before tourniquet inflation could reduce TIH, and tourniquet pain with reduction in intraoperative IV fentanyl and postoperative pethidine requirements.