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

Abstract 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. 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. 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