Continuous Popliteal Sciatic Blocks: Does Varying Perineural Catheter Location Relative to the Sciatic Bifurcation Influence Block Effects? A Dual-Center, Randomized, Subject-Masked, Controlled Clinical Trial

Abstract

Background Multiple studies have demonstrated that, for single-injection popliteal sciatic nerve blocks, block characteristics are dependent upon local anesthetic injection relative to the sciatic nerve bifurcation. In contrast, this relationship remains unexamined for continuous popliteal sciatic nerve blocks. We therefore tested the hypothesis that postoperative analgesia is improved with the perineural catheter tip at the level of the bifurcation compared to 5 cm proximal to the bifurcation. Methods Preoperatively, subjects having moderately painful foot or ankle surgery were randomly assigned to receive an ultrasound-guided subepimyseal perineural catheter inserted either at or 5 cm proximal to the sciatic nerve bifurcation. Subjects received a single injection of mepivacaine 1.5% either via the insertion needle preoperatively or the perineural catheter postoperatively, followed by an infusion of ropivacaine 0.2% (6 mL/h basal, 4 mL bolus, 30 min lockout) for the study duration. The primary end point was the average pain measured on a numeric rating scale (NRS; 0-10) in the 3 hours prior to a data collection telephone call the morning after surgery. Results The average NRS of subjects with a catheter inserted at the sciatic nerve bifurcation (n=64) was a median [10th, 25th-75th, 90th quartiles] of 3.0 [0.0, 2.4-5.0, 7.0] versus 2.0 [0.0, 1.0-4.0, 5.0] for subjects with a catheter inserted proximal to the bifurcation (n=64; P=0.008). Similarly, maximum pain scores were higher in the group at the bifurcation: 6.0 [3.0, 4.4-8.0, 9.0] versus 5.0 [0.0, 3.0-8.0, 10.0] (P=0.019). Differences between the groups for catheter insertion time, opioid rescue dose, degree of numbness in the foot/toes, catheter dislodgement, and fluid leakage did not reach statistical significance. Conclusions For continuous popliteal sciatic nerve blocks, a catheter inserted 5 cm proximal to the sciatic nerve bifurcation provides superior postoperative analgesia in subjects having moderately painful foot or ankle surgery compared with catheters located at the bifurcation. This is in marked contrast with single-injection popliteal sciatic nerve blocks for which benefits are afforded to local anesthetic injection distal, rather than proximal, to the bifurcation.

Continuous Popliteal-Sciatic Blocks for Postoperative Analgesia: Traditional Proximal Catheter Insertion Superficial to the Paraneural Sheath Versus a New Distal Insertion Site Deep to the Paraneural Sheath

“…The original power analysis was based on an approximation using the 2-sample t test. Using an expected numeric rating scale mean = 2.6 and standard deviation = 2.1 of average pain, 11 approximately 31 subjects in each treatment arm were required to detect a difference between treatment group means of 1.5 with a 2-sided α = .05 and power = 0.8 (ClinCalc.com, accessed June 28, 2015).…”

“…12 Subsequently, ultrasound guidance allowed for precise administration relative to the bifurcation, and evidence mounted that benefits are afforded with local anesthetic administration distal versus proximal to the bifurcation for single-injection popliteal blocks. [4][5][6] Previously, we attempted to duplicate these findings for continuous popliteal blocks but discovered the opposite relationship for perineural infusion: postoperative analgesia was superior when the catheter was inserted proximal compared with at the sciatic bifurcation, 11 suggesting that no change from the traditional approach was indicated. However, all of these studies were designed before widespread knowledge within the regional anesthesia community of the importance of the paraneural sheath, 7,13 and the great majority of local anesthetic administration for the initial investigations was most likely superficial to the paraneurium for all treatments.…”

Basal InfusionversusAutomated Boluses and a Delayed Start Timer for “Continuous” Sciatic Nerve Blocks after Ambulatory Foot and Ankle Surgery: A Randomized Clinical Trial

“…( C ) Discrete distribution used for simulations based on the distribution observed in the above bifurcation group in the work of Monahan et al . 29…”

“…Power was simulated based on the distribution of the numeric rating scale observed in previously published studies of pain scores after foot and ankle surgery with a continuous popliteal-sciatic infusion. 29 Specifically, numeric rating scale scores were simulated from a discrete distribution that generated an expected interquartile range from 1 to 4, and a median of 3 numeric rating scale units. One thousand trials were simulated in which two groups, n = 35 per group, were assumed to follow the same discrete distribution (fig.…”

“…(Left) noninferiority margin shown as a dashed line at -1.7 units on a numeric rating scale. (C) Discrete distribution used for simulations based on the distribution observed in the above bifurcation group in the work of Monahan et al29…”