[Control of postoperative pain in knee arthroplasty: single dose femoral nerve block versus continuous femoral block].

INTRODUCTION: To compare the efficacy of a multimodal analgesia with 2 different techniques (femoral nerve block with a single dose and continuous femoral nerve block) in the control of pain, use of opioids, and secondary effects in patients subjected to total knee replacement.

MATERIAL AND METHODS: A prospective randomised study of patients subjected to knee replacement with subarachnoid anaesthesia. The postoperative analgesia consisted of tramadol, dexketoprofen and paracetamol, and one of the following techniques: Femoral nerve block with a single dose of 30mL of 0.5% ropivacaine, or that dose plus a continuous infusion via a femoral catheter of 0.375% ropivacaine 6ml/h for 48h. The demographic, anaesthetic and surgical variables were recorded, along with the pain intensity using a visual analogue scale, opioid use, and complications at 24 and 48h after surgery.

RESULTS: A total of 104 patients were included. There no differences in the demographic data between the groups. The pain intensity was lower in the group that had continuous femoral block, particularly at 48h, compared to the single-dose block, and with a lower use of rescue analgesia in the continuous femoral block. The incidence in secondary effects was similar, with a lower long-term sensory block being observed in the femoral block with a single dose.

CONCLUSIONS: The use of peripheral nerve block is accepted practice for analgesia after knee replacement surgery. Continuous femoral block is a valid alternative, decreasing the use of rescue opiates and pain intensity (particularly at 48h) compared to isolated femoral block.