Does the Addition of Magnesium Sulfate to Continuous Femoral Block in Knee Arthroplasty Decrease Postoperative Analgesic Requirements?

Abstract

Objectives: We aimed to determine the effect of magnesium infusion added to continuous femoral nerve block on postoperative opioid consumption and pain scores in total knee arthroplasty. Materials and Methods: Sixty-five American Society of Anesthesiologists I-II patients who were between 18 and 65 years of age, scheduled to undergo elective unilateral knee arthroplasty, were recruited and randomized into groups LM and L. All patients were given 30 mL 0.5% levobupivacaine and 1 mL 1:200.000 adrenaline through a femoral catheter. Arthroplasty was performed under spinal anesthesia using 10 mg hyperbaric bupivacaine. Patients in group LM (n=30) were given 40 mg MgSO4 in normal saline as intravenous infusion over 20 minutes intraoperatively and 12 mg MgSO4 in 240 mL 10 mL/h normal saline over 24 hours postoperatively. Patients in group L (n=30) were given 100 mL normal saline over 20 minutes intraoperatively and 240 mL normal saline 10 mL/h over 24 hours postoperatively. All patients were given 0.125% 10 mL/h levobupivacaine via the femoral catheter and morphine intravenous patient controlled anesthesia for 24 hours postoperatively in addition to acetaminophen 4x1 g and lornoxicam 2x8 mg. Hemodynamic parameters, opioid consumption and pain at rest and movement were recorded at 1, 2, 4, 6, 12, 24, 36 and 48th postoperative hours. Results: The patients in group LM had significantly lower resting visual analogue score (VAS) and verbal pain rating score (VPRS) scores at the postoperative 4, 6, 12 and 24th hours. VAS and VPRS scores during movement were significantly lower in group LM at postoperative 12 and 24th hours. Total opioid consumption was 11.6±4.6 mg in group L and 9.8±4.3 mg in group LM (p=0.032). Conclusion: Multimodal analgesia is necessary when the effects of postoperative pain on morbidity and mortality following total knee arthroplasties are considered and magnesium added to continuous femoral nerve block, intravenous morphine PCA, lornoxicam and acetaminophen provides effective pain control as a part of multimodal analgesia.