Eliza J. Ferguson

Continuous Femoral Nerve Blocks: Varying Local Anesthetic Delivery Method (Bolus versus Basal) to Minimize Quadriceps Motor Block while Maintaining Sensory Block

Background: Whether the method of local anesthetic administration for continuous femoral nerve blocks—basal infusion versus repeated hourly bolus doses—influences block effects remains unknown. Methods: Bilateral femoral perineural catheters were inserted in volunteers (n = 11). Ropivacaine 0.1% was concurrently administered through both catheters: a 6-h continuous 5 ml/h basal infusion on one side and 6 hourly bolus doses on the contralateral side. The primary endpoint was the maximum voluntary isometric contraction (MVIC) of the quadriceps femoris muscle at hour 6. Secondary endpoints included quadriceps MVIC at other time points, hip adductor MVIC, and cutaneous sensation 2 cm medial to the distal quadriceps tendon in the 22 h after initiation of local anesthetic administration. Results: Quadriceps MVIC for limbs receiving 0.1% ropivacaine as a basal infusion declined by a mean (SD) of 84% (19) compared with 83% (24) for those receiving 0.1% ropivacaine as repeated bolus doses between baseline and hour 6 (paired t test P = 0.91). Intrasubject comparisons (left vs. right) also reflected a lack of difference: the mean basal-bolus difference in quadriceps MVIC at hour 6 was −1.1% (95% CI −22.0–19.8%). The similarity did not reach the a priori threshold for concluding equivalence, which was the 95% CI decreasing within ± 20%. There were similar minimal differences in the secondary endpoints during local anesthetic administration. Conclusions: This study did not find evidence to support the hypothesis that varying the method of local anesthetic administration—basal infusion versus repeated bolus doses—influences continuous femoral nerve block effects to a clinically significant degree.

Continuous peripheral nerve blocks: is local anesthetic dose the only factor, or do concentration and volume influence infusion effects as well?

Background:The main determinant of continuous peripheral nerve block effects—local anesthetic concentration and volume or simply total drug dose—remains unknown. Methods:We compared two different concentrations and basal rates of ropivacaine—but at equivalent total doses—for continuous posterior lumbar plexus blocks after hip arthroplasty. Preoperatively, a psoas compartment perineural catheter was inserted. Postoperatively, patients were randomly assigned to receive perineural ropivacaine of either 0.1% (basal 12 ml/h, bolus 4 ml) or 0.4% (basal 3 ml/h, bolus 1 ml) for at least 48 h. Therefore, both groups received 12 mg of ropivacaine each hour with a possible addition of 4 mg every 30 min via a patient-controlled bolus dose. The primary endpoint was the difference in maximum voluntary isometric contraction (MVIC) of the ipsilateral quadriceps the morning after surgery, compared with the preoperative MVIC, expressed as a percentage of the preoperative MVIC. Secondary endpoints included hip adductor and hip flexor MVIC, sensory levels in the femoral nerve distribution, hip range-of-motion, ambulatory ability, pain scores, and ropivacaine consumption. Results:Quadriceps MVIC for patients receiving 0.1% ropivacaine (n = 26) declined by a mean (SE) of 64.1% (6.4) versus 68.0% (5.4) for patients receiving 0.4% ropivacaine (n = 24) between the preoperative period and the day after surgery (95% CI for group difference: −8.0–14.4%; P = 0.70). Similarly, the groups were found to be equivalent with respect to secondary endpoints. Conclusions:For continuous posterior lumbar plexus blocks, local anesthetic concentration and volume do not influence nerve block characteristics, suggesting that local anesthetic dose (mass) is the primary determinant of perineural infusion effects.

Ultrasound Guidance Versus Electrical Stimulation for Infraclavicular Brachial Plexus Perineural Catheter Insertion

Objective. Electrical stimulation (ES)‐ and ultrasound‐guided placement techniques have been described for infraclavicular brachial plexus perineural catheters but to our knowledge have never been previously compared in a randomized fashion, leaving the optimal method undetermined. We tested the hypothesis that infraclavicular catheters placed via ultrasound guidance alone require less time for placement and produce equivalent results compared with catheters placed solely via ES. Methods. Preoperatively, patients receiving an infraclavicular perineural catheter for distal upper extremity surgery were randomly assigned to either ES with a stimulating catheter or ultrasound guidance with a nonstimulating catheter. The primary outcome was the catheter insertion duration (minutes) starting when the ultrasound transducer (ultrasound group) or catheter placement needle (stimulation group) first touched the patient and ending when the catheter placement needle was removed after catheter insertion. Results. Perineural catheters placed with ultrasound guidance took a median (10th–90th percentile) of 9.0 (6.0–13.2) minutes compared with 15.0 (4.9–30.0) minutes for stimulation (P < .01). All ultrasound‐guided catheters were successfully placed according to the protocol (n = 20) versus 70% in the stimulation group (n = 20; P < .01). All ultrasound‐guided catheters resulted in a successful surgical block, whereas 2 catheters placed by stimulation failed to result in surgical anesthesia. Six catheters (30%) placed via stimulation resulted in vascular punctures compared with none in the ultrasound group (P < .01). Procedure‐related pain scores were similar between groups (P = .34). Conclusions. Placement of infraclavicular perineural catheters takes less time, is more often successful, and results in fewer inadvertent vascular punctures when using ultrasound guidance compared with ES.

A randomized comparison of infraclavicular and supraclavicular continuous peripheral nerve blocks for postoperative analgesia.

Background: Although the efficacy of single-injection supraclavicular nerve blocks is well established, no controlled study of continuous supraclavicular blocks is available, and their relative risks and benefits remain unknown. In contrast, the analgesia provided by continuous infraclavicular nerve blocks has been validated in randomized controlled trials. We therefore compared supraclavicular with infraclavicular perineural local anesthetic infusion following distal upper-extremity surgery. Methods: Preoperatively, subjects were randomly assigned to receive a brachial plexus perineural catheter in either the infraclavicular or supraclavicular location using an ultrasound-guided nonstimulating catheter technique. Postoperatively, subjects were discharged home with a portable pump (400-mL reservoir) infusing 0.2% ropivacaine (basal rate of 8 mL/hr; 4-mL bolus dose; 30-min lockout interval). Subjects were followed up by telephone on an outpatient basis. The primary outcome was the average pain score on the day after surgery. Results: Sixty subjects were enrolled, with 31 and 29 randomized to receive an infraclavicular and supraclavicular catheter, respectively. All perineural catheters were successfully placed per protocol. Because of protocol violations and missing data, an intention-to-treat analysis was not used; rather, only subjects with catheters in situ and whom we were able to contact were included in the analyses. The day after surgery, subjects in the infraclavicular group reported average pain as median of 2.0 (10th-90th percentiles, 0.5-6.0) compared with 4.0 (10th-90th percentiles, 0.6-7.7) in the supraclavicular group (P = 0.025). Similarly, least pain scores (numeric rating scale) on postoperative day 1 were lower in the infraclavicular group compared with the supraclavicular group (0.5 [10th-90th percentiles, 0.0-3.5] vs 2.0 [10th-90th percentiles, 0.0-4.7], respectively; P = 0.040). Subjects in the infraclavicular group required less rescue oral analgesic (oxycodone, in milligrams) for breakthrough pain in the 18 to 24 hrs after surgery compared with the supraclavicular group (0.0 [10th-90th percentiles, 0.0-5.0] vs 5.0 [10th-90th percentiles, 0.0-15.0], respectively; P = 0.048). There were no statistically significant differences in other secondary outcomes. Conclusions: A local anesthetic infusion via an infraclavicular perineural catheter provides superior analgesia compared with a supraclavicular perineural catheter.

A Trainee-Based Randomized Comparison of Stimulating Interscalene Perineural Catheters With a New Technique Using Ultrasound Guidance Alone

Objective. Compared to the well‐established stimulating catheter technique, the use of ultrasound guidance alone for interscalene perineural catheter insertion is a recent development and has not yet been examined in a randomized fashion. We hypothesized that an ultrasound‐guided technique would require less time and produce equivalent results compared to electrical stimulation (ES) when trainees attempt interscalene perineural catheter placement. Methods. Preoperatively, patients receiving an interscalene perineural catheter for shoulder surgery were randomly assigned to an insertion protocol using either ultrasound guidance with a nonstimulating catheter or ES with a stimulating catheter. The primary outcome was the procedural duration (in minutes), starting when the ultrasound probe (ultrasound group) or catheter insertion needle (ES group) first touched the patient and ending when the catheter insertion needle was removed after catheter insertion. Results. All ultrasound‐guided catheters (n = 20) were placed successfully and resulted in surgical anesthesia versus 85% of ES‐guided catheters (n = 20; P = .231). Perineural catheters placed by ultrasound (n = 20) took a median (10th–90th percentiles) of 8.0 (5.0–15.5) minutes compared to 14.0 (5.0–30.0) minutes for ES (n = 20; P = .022). All catheters placed according to the protocol in both treatment groups resulted in a successful nerve block; however, 1 patient in the ES group had local anesthetic spread to the epidural space. There was 1 vascular puncture using ultrasound guidance compared to 5 in the ES‐guided catheter group (P = .182). Conclusions. Trainees using a new ultrasound‐guided technique can place inter‐scalene perineural catheters in less time compared to a well‐documented technique using ES with a stimulating catheter and can produce equivalent results.

Continuous Transversus Abdominis Plane (TAP) Blocks for Postoperative Pain Control after Hernia Surgery: A Randomized, Triple-Masked, Placebo-Controlled Study

BACKGROUND Single-injection transversus abdominis plane (TAP) block provides postoperative analgesia and decreases supplemental analgesic requirements. However, there is currently no evidence from randomized, controlled studies investigating the possible benefits of continuous TAP blocks. Therefore, the aim of this randomized, triple-masked, placebo-controlled study was to determine if benefits are afforded by adding a multiple-day, ambulatory, continuous ropivacaine TAP block to a single-injection block following hernia surgery. METHODS Preoperatively, subjects undergoing unilateral inguinal (N=19) or peri-umbilical (N=1) hernia surgery received unilateral or bilateral TAP perineural catheter(s), respectively. All received a ropivacaine 0.5% (20 mL) bolus via the catheter(s). Subjects were randomized to either postoperative perineural ropivacaine 0.2% or normal saline using portable infusion pump(s). Subjects were discharged home where the catheter(s) were removed the evening of postoperative day (POD) 2. Subjects were contacted on POD 0-3. The primary endpoint was average pain with movement (scale: 0-10) queried on POD 1. RESULTS Twenty subjects of a target 30 were enrolled due to the primary surgeons unanticipated departure from the institution. Average pain queried on POD 1 for subjects receiving ropivacaine (N=10) was a mean (standard deviation) of 3.0 (2.6) vs 2.8 (2.7) for subjects receiving saline (N=10; 95% confidence interval difference in means -2.9 to 3.4; P=0.86). There were no statistically significant differences detected between treatment groups in any secondary endpoint. CONCLUSIONS The results of this study do not support adding an ambulatory, continuous ropivacaine infusion to a single-injection ropivacaine TAP block for hernia surgery. However, the present investigation was underpowered, and further study is warranted.

Ultrasound-guided root/trunk (interscalene) block for hand and forearm anesthesia.

Background Historically, the anterolateral interscalene block—deposition of local anesthetic adjacent to the brachial plexus roots/trunks—has been used for surgical procedures involving the shoulder. The resulting block frequently failed to provide surgical anesthesia of the hand and forearm, even though the brachial plexus at this level included all of the axons of the upper-extremity terminal nerves. However, it remains unknown whether deposition of local anesthetic adjacent to the seventh cervical root or inferior trunk results in anesthesia of the hand and forearm. Methods Using ultrasound guidance and a needle-in-plane posterior approach, a Tuohy needle was positioned with the tip located between the deepest and next-deepest visualized brachial plexus root/trunk, followed by injection of mepivacaine (1.5%). Grip strength and the tolerance to cutaneous electrical current in 5 terminal nerve distributions were measured at baseline and then every 5 minutes following injection for a total of 30 minutes. The primary end point was the proportion of cases in which the interscalene nerve block resulted in a decrease in grip strength of at least 90% and hand and forearm anesthesia (tolerance to >50 mA of current in all 5 terminal nerve distributions) within 30 minutes. The primary hypothesis was that a single-injection interscalene brachial plexus block produces a similar rate of anesthesia of the hand and forearm to the published success rate of 95% for other brachial plexus block approaches. Results Of 55 subjects with blocks placed per protocol, all had a successful block of the shoulder as defined by inability to abduct at the shoulder joint. Thirty-three subjects had measurements at 30 minutes following local anesthetic deposition, and only 5 (15%) of these subjects had a surgical block of the hand and forearm (P < 0.0001; 95% confidence interval, 6%–33%). We therefore reject the hypothesis that the interscalene block as performed in this study provides equivalent anesthesia to the hand and forearm compared with other brachial plexus block techniques. Block failures of the hand and forearm were due to inadequate cutaneous anesthesia of the ulnar (n = 27; 82%), median (n = 26; 78%), or radial (n = 22; 67%) distributions; the medial forearm (n = 25; 76%); and/or the lateral forearm (n = 14; 42%). Failure to achieve at least a 90% reduction in grip strength occurred in 16 subjects (48%). Conclusions This study did not find evidence to support the hypothesis that local anesthetic injected adjacent to the deepest brachial plexus roots/trunks reliably results in surgical anesthesia of the hand and forearm.