Intravenous infusion of magnesium sulfate and postoperative analgesia in total knee arthroplasty

Background. The effectiveness of combining magnesium (Mg) administration with both general and spinal anesthesia to reduce postoperative pain and analgesic consumption is still debated: We evaluated the effects of an intravenous (IV) infusion of Mg sulphate on analgesic consumption and postoperative pain score after total knee arthroplasty performed under spinal anesthesia.Methods. We studied 40 patients who underwent spinal anesthesia with bupivacaine plus morphine. Patients were randomly assigned to two groups, each of 20 patients, who received either treatment (i.e., intravenous Mg sulphate 40 mg kg(-1) followed by an infusion of 10 mg kg(-1) h(-1)), or the same amounts of isotonic saline (controls). Irrespective of the group of randomization, all patients received postoperative paracetamol, ketorolac, and patient-controlled analgesia with morphine.Results. The Mg postoperative blood level was 0.85 +/- 0.02 mmol/L and 1.25 +/- 0.11 mmol/L for C and Mg groups, respectively (P<0.001). Sensory level of the spinal block, height of spinal block, mean time to first pain and incidence of PONY were similar in the two groups. Morphine consumption did not show any statistically significant difference between the two groups. The pain score was not significantly different between the two groups. No severe adverse effects were recorded after Mg infusion.Conclusion. IV perioperative administration of Mg did not influence postoperative pain control and analgesic consumption after total knee arthroplasty. More studies should be performed with different intra and postoperative pain protocols to enhance the potential anti-nociceptive effect of Mg.