Effectiveness of adding ketamine to ropivacaine infusion via femoral nerve catheter after knee anterior cruciate ligament repair

BACKGROUND Elective knee surgery for repairing anterior cruciate ligament is usually associated with moderate to severe postoperative pain, and, therefore, selecting appropriate analgesia can considerably facilitate pain control and patient's discharge. This study was designed to compare the analgesic effectiveness of administration of ropivacaine or ropivacaine plus ketamine on pain control and improvement of muscle weakness after anterior cruciate ligament repair in adults. MATERIALS AND METHODS A double-blind randomized study which performed in Operating room and Sixty six patients with American Society of Anesthesiologists health status I to II that underwent elective knee surgery for repairing anterior cruciate ligament under spinal anesthesia were enrolled. Patients were randomly allocated to receive either ropivacaine 0.2% or an equivalent volume of ropivacaine 0.1% plus 1.0 mg/kg ketamine via continuous femoral block with pump infusion. The patients were familiarized with a 10-point verbal analog scale. Quadriceps muscle weakness and sedation score were assessed based on relevant scales. Parameters assessment were obtained from all patients immediately after PACU entrance, and postoperative assessment was performed at 4, 8, 12, 16, 20, 24, 30, 36, 42, and 48 h after the operation. RESULTS The data of 31 patients who received ropivacaine and of 33 patients in ketamine-ropivacaine group were eligible for analysis. Visual analogue scale (VAS) scores differed at various time points after surgery, with higher scores in patients who received concomitant ketamine and ropivacaine (P < 0.05). The degree of quadriceps muscle weakness was similar between the groups at the different time points. Patients in ropivacaine group rated better quality of pain control with appropriate sedation in comparison with the patients in ketamine/ropivacaine group. CONCLUSION Our study shows that the addition of a ketamine 1 mg/kg to 0.1% ropivacaine via pump infusion after repairing anterior cruciate ligament could not improve pain control and muscle weakness.