Optimizing dose infusion of 0.125% bupivacaine for continuous femoral nerve block after total knee replacement

BACKGROUND: The optimal dose infusion of 0.125% bupivacaine via a femoral catheter after total knee replacement (TKR) has not been defined. This study examined various dose infusions of bupivacaine to determine the analgesic quality in patients receiving a continuous femoral nerve block (CFNB). METHODS: Patients were randomized to receive a single-injection femoral nerve block (SFNB) or CFNB performed with 20 ml of 0.125% bupivacaine, followed by a continuous infusion of 0.125% bupivacaine in four groups (n = 20 per group): 1) 0 ml/h (SFNB), 2) 2 ml/h, 3) 4 ml/h, and 4) 6 ml/h. The pain intensity at rest and on knee movement was assessed using a visual analog scale (VAS) for the first 2 postoperative days. The cumulative bolus use of IV patientcontrolled analgesia (PCA) with a morphine-ketorolac combination was evaluated. RESULTS: A lower cumulative bolus of IV PCA was noted in all CFNB groups compared to SFNB on postoperative days (PODs) 1 and 2, respectively (P < 0.05). Lower VAS scores at rest were observed in the 4 ml/h and 6 ml/h groups than in the SFNB group on PODs 1 and 2, respectively, but only on POD 2 in the 2 ml/h group (P < 0.05). Lower VAS scores on movement were noted in the 4 ml/h than the SFNB group on PODs 1 and 2, but only on POD 1 in 6 ml/h (P < 0.05). CONCLUSIONS: The minimum effective infusion rate of 0.125% bupivacaine for CFNB after TKR appears to be 4 ml/h according to the VAS pain scores.