Magnesium sulfate does not reduce postoperative analgesic requirements

Background: Because magnesium blocks the N-methyl-D-aspartate receptor and its associated ion channels, it can prevent central sensitization caused by peripheral nociceptive stimulation. However, transport of magnesium from b lood to cerebrospinal fluid (CSF) across the blood-brain harrier is limited In normal humans. The current stud), was designed to evaluate whether peri operative intravenous magnesium sulfate infusion affects postoperative pain . Methods: Sixty patients undergoing abdominal hysterectomy received 50 mg/kg intravenous magnesium sulfate as a bolus close followed by a continuous in fusion of 15 mg (.) kg(-1) (.) h(-1) for 6 h (magnesium group) or the same volume of isotonic saline (control group). At the end of surgery, serum and CSF magnesium concentration were measured in both groups. The cumulative p ostoperative analgesic consumption was measured to assess the analgesic eff ect using a patient-controlled epidural analgesia device. Pain intensities at rest and during forced expiration were evaluated at 6, 24, 48, and 72 h postoperatively. Results: At the end of surgery, patients in the magnesium group had signifi cantly greater postoperative serum magnesium concentrations compared with b oth preoperative and control group values (P < 0.001). Despite significantl y higher serum magnesium concentrations in the magnesium group, there was n o significant difference in magnesium concentration measured in postoperati ve CSF. Cumulative postoperative analgesic doses were similar in both group s. However, there was observed an inverse relation between cumulative posto perative analgesic consumption and the CSF magnesium concentration in both groups. Visual analog pain scores at rest and during forced expiration were similar and less than 4 in both groups. Conclusions: Perioperative intravenous administration of magnesium sulfate did not Increase CSF magnesium concentration and had no effects on postoper ative pain. However, an inverse relation between cumulative postoperative a nalgesic consumption and the CSF magnesium concentration was observed. Thes e results suggest that perioperative intravenous magnesium infusion may not be useful for preventing postoperative pain.