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

Abstract

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.

Keywords: Femoral nerve block; Patient-controlled analgesia; Visual analog scale.

Fig. 1

Frontal radiographs of the pelvic region show the location of the catheter tip (arrows) and the spread of the 3 ml of contrast media. (A) The tip is located under the iliac fascia covering the psoas major muscle (medial). (B) The tip of the catheter is located between the medial and lateral position (intermediate). (C) The tip is located under the iliac fascia covering the iliacus muscle (lateral).

Fig. 2

This figure shows the zones reached by the spread of the local anesthetic under the fascia iliaca. (A) Internal spread under the psoas muscle fascia. (B) External spread under the iliacus muscle fascia. (C) Spread to the roots of the lumbar plexus. 1 = lateral femoral cutaneous nerve, 2 = femoral nerve, 3 = obturator nerve (Reprinted from Capdevila et al.'s study [8]).

Fig. 3

This diagram compares the cumulative postoperative consumption of IV PCA (ml) by patients in the four groups during the first postoperative 2 days. All CFNB groups show lower cumulative PCA bolus use of morphine plus ketorolac than the control on PODs 1 and 2, respectively. PCA: patient-controlled analgesia, CFNB: continuous femoral nerve block, PACU: postanesthesia care unit, POD: postoperative day. ^*P < 0.05 compared to the 0 ml/h group.

Fig. 4

This diagram compares the VAS pain scores at rest in the four groups. The VAS scores at rest are significantly lower in the 4 ml/h and 6 ml/h groups than the control on PODs 1 and 2, respectively, but only on POD 2 in 2 ml/h. VAS: visual analog scale, PACU: postanesthesia care unit, POD: postoperative day. ^*P < 0.05 compared to the 0 ml/h group.

Fig. 5

This diagram compares the VAS pain scores on movement in the four groups. The VAS scores on movement in the 4 ml/h group are significantly lower than the control on PODs 1 and 2, but only on POD 1 in 6 ml/h. VAS: visual analog scale, PACU: postanesthesia care unit, POD: postoperative day. ^*P < 0.05 compared to the 0 ml/h group.