Building Affordable, Durable, Medium-fidelity Ballistic Gel Phantoms for Ultrasound-guided Nerve Block Training.

Ultrasound phantoms - alternatives to live human tissue - give learners the opportunity to practice ultrasound-guided regional anesthesia without introducing undue risk to patients. Gelatin-based phantoms provide educators with durable and reusable task trainers; however, commercially available gel-based phantoms are expensive. Here, we investigate the production of durable, low-cost, ballistic gel-based ultrasound phantoms for median, femoral, suprainguinal fascia iliaca plane, and serratus anterior plane nerve blocks, as well as a methodology for producing a phantom for any ultrasound-guided nerve block procedure. Computer-aided design (CAD) software was utilized to design four phantoms replicating the anatomy of median, femoral, suprainguinal fascia iliaca plane, and serratus anterior plane nerve blocks, including relevant landmarks and tissue planes. Plastic models of the desired tissue planes were 3D printed and used to create silicone molds. Ballistic gel was melted and mixed with flour and dye to create a liquid, echogenic ballistic gel, which was poured into the silicone molds. Vessels were simulated by creating negative space in the ballistic gel using metal rods. Nerves were simulated using yarn submerged in ultrasound gel. Simulated bones were designed using CAD and 3D printed. Ballistic gel is a versatile, durable medium that can be used to simulate a variety of tissues and can be melted and molded into any shape. Under ultrasound, these phantoms provide realistic tissue planes that represent the borders between different layers of skin, muscle, and fascia. The echogenicity of the muscle tissue layers, nerves, vessels, and bones is realistic, and bones have significant posterior shadowing as would be observed in a human subject. These phantoms cost $200 each for the first phantom and $60 for each subsequent phantom. These phantoms require some technical skill to design, but they can be built for just 4% of the cost of their commercial counterparts.

Relative Effects of Various Factors on Ice Ball Formation and Ablation Zone Size During Ultrasound-Guided Percutaneous Cryoneurolysis: A Laboratory Investigation to Inform Clinical Practice and Future Research.

INTRODUCTION: Ultrasound-guided percutaneous cryoneurolysis provides analgesia using cold temperatures to reversibly ablate peripheral nerves. Cryoneurolysis probes pass a gas through a small internal annulus, rapidly lowering the pressure and temperature, forming an ice ball to envelope the target nerve. Analgesia is compromised if a nerve is inadequately frozen, and laboratory studies suggest that pain may be paradoxically induced with a magnitude and duration in proportion with the incomplete ablation. We therefore investigated the relative effects of various factors that may contribute to the size of the ice ball and the effective cryoneurolysis zone. METHODS: A cryoprobe was inserted into a piece of meat, a gas was passed through for 2 min, and the resulting ice ball width (cross-section) and length (axis parallel to the probe) were measured using ultrasound, with the temperature evaluated in nine concentric locations concurrently. RESULTS: The factor with the greatest influence on ice ball size was probe gauge: in all probe types, a change from 18 to 14 increased ice ball width, length, and volume by up to 70%, 113%, and 512% respectively, with minimum internal temperature decreasing as much as from -5 to -32 °C. In contrast, alternating the type of meat (chicken, beef, pork) and the shape of the probe tip (straight, coudé) affected ice ball dimensions to a negligible degree. The ice ball dimensions and the zone of adequate temperature drop were not always correlated, and, even within a visualized ice ball, the temperature was often inadequate to induce Wallerian degeneration. CONCLUSIONS: Percutaneous probe design can significantly influence the effective cryoneurolysis zone; visualizing a nerve fully encompassed in an ice ball does not guarantee adequate treatment to induce the desired Wallerian degeneration because ice forms at temperatures between 0 and -20 °C, whereas only temperatures below -20 °C induce Wallerian degeneration. The correlation between temperatures in isolated pieces of meat and perfused human tissue remains unknown, and further research to evaluate these findings in situ appears highly warranted.

COVID-19 educational innovation: Hybrid in-person and virtual simulation for emergency medicine trainees.

The COVID-19 pandemic has dramatically affected medical education. Emergency medicine (EM) requires excellence in multiple core competencies, including leadership, teamwork, and communication skills as well as procedural experience. To meet these objectives, we developed a hybrid simulation model that accommodated a reduced number of learners in our simulation center to allow for physical distancing, seamlessly integrated with an online integrated experience for remote learners. All learners participated or watched one adult and one pediatric simulation case. Fourteen residents participated in live simulation, while six residents and six medical students comprised the remote group. At the end of each case, the live feed was ended, and separate debriefings were conducted by different EM faculty, in person and online (via Zoom). An electronic survey was then sent to participants to rate the effectiveness of the intervention; 23 survey responses were collected: 52.2% (12) from the live session and 47.2% (11) from the virtual session. Survey results demonstrated that the online simulation observation and debriefing had the same, if not better, satisfaction than in-person simulation sessions and debriefings. Due to its success, this new method of hybrid simulation will be our plan for the foreseeable future, at least until COVID-19 abates.

Predicting Trainee Clinical Success From Performance at Simulated Endotracheal Intubation.

INTRODUCTION: Multiple attempts and failure at endotracheal intubation (ETI) are common for inexperienced practitioners and can cause patient morbidity. A test to predict a provider's likelihood of success at patient ETI could assist decisions about training. This project investigated whether trainees' performance at laryngoscopy on airway mannequins predicted their laryngoscopy outcomes in patients. METHODS: Twenty-one consenting first-year anesthesiology residents, emergency medicine residents, and medical students enrolled in this prospective, observational study. They performed laryngoscopy and ETI with a curved laryngoscope on 4 airway mannequins. Metrics included peak dental force, procedure duration, esophageal intubation, laryngeal view, and first-pass ETI success on the mannequins. Trainee data from 203 patient ETIs were collected over a roughly 2-month period centered around the simulation test. Multivariable logistic regression analyzed the relationship of mannequin metrics, participant experience, and a patient difficult airway score with trainee ETI outcomes in patients. RESULTS: Median trainee first-pass success rate at patient ETI was 63%, the rate of ETI problems was 16%, and the esophageal intubation rate was 6%. Laryngoscopy peak dental force, first-pass ETI success, and duration on individual mannequins were significant predictors of patient ETI first-pass success. Metrics from 2 of the 4 mannequins predicted ETI problems. DISCUSSION: Performance metrics from simulated laryngoscopy predicted trainee outcomes during patient ETI. First-pass success and ETI problems affect patient safety and are related to trainee skill. Mannequin laryngoscopy tests could identify trainees who would benefit from additional practice. The metrics could be surrogate end points in research to optimize simulated laryngoscopy training.

An integrated microcatheter-based dual-analyte sensor system for simultaneous, real-time measurement of propofol and fentanyl.

According to the American Society of Anesthesiologists Closed Claims Database, one of three drug-related errors is the result administrating an incorrect dose. Directly measuring drug concentration removes the uncertainty in the dose-concentration relationship and addresses inter- and intra-subject variabilities that affect the pharmacokinetics of anesthetics. Here we describe a dual-analyte microcatheter-based electrochemical sensor capable of simultaneous real-time continuous monitoring of fentanyl (FTN) and propofol (PPF) drugs simultaneously in the operating rooms. Such a dual PPF/FTN catheter sensor relies on embedding two different modified carbon paste (CP)-packed working electrodes along with Ag/AgCl microwire reference electrodes within a mm-wide Teflon tube, and uses a square wave voltammetric (SWV) technique. The composition of each working electrode was judiciously tailored to cover the concentration range of interest for each analyte. A polyvinyl chloride (PVC) organic polymer coating on the surface of CP electrode enabled selective and sensitive PPF measurements in µM range. The detection of nM FTN levels was achieved through a multilayered nanostructure-based surface modification protocol, including a CNT-incorporated CP transducer modified by a hybrid of electrodeposited Au nanoparticles and electrochemically reduced graphene oxide (erGO) and a PVC outer membrane. The long-term monitoring capability of the dual sensor was demonstrated in a protein-rich artificial plasma medium. The promising antibiofouling behavior of the catheter-based multiplexed sensor was also illustrated in whole blood samples. The new integrated dual-sensor microcatheter platform holds considerable promise towards real-time, in-vivo detection of the anesthetic drugs, propofol and fentanyl, during surgical procedures towards significantly improved safe delivery of anesthetic drugs.

MADVent: A low-cost ventilator for patients with COVID-19.

The COVID-19 pandemic has produced critical shortages of ventilators worldwide. There is an unmet need for rapidly deployable, emergency-use ventilators with sufficient functionality to manage COVID-19 patients with severe acute respiratory distress syndrome. Here, we show the development and validation of a simple, portable and low-cost ventilator that may be rapidly manufactured with minimal susceptibility to supply chain disruptions. This single-mode continuous, mandatory, closed-loop, pressure-controlled, time-terminated emergency ventilator offers robust safety and functionality absent in existing solutions to the ventilator shortage. Validated using certified test lungs over a wide range of compliances, pressures, volumes and resistances to meet U.S. Food and Drug Administration standards of safety and efficacy, an Emergency Use Authorization is in review for this system. This emergency ventilator could eliminate controversial ventilator rationing or splitting to serve multiple patients. All design and validation information is provided to facilitate ventilator production even in resource-limited settings.

Post-mastectomy cancer recurrence with and without a continuous paravertebral block in the immediate postoperative period: a prospective multi-year follow-up pilot study of a randomized, triple-masked, placebo-controlled investigation.

PURPOSE: Retrospective studies have associated perioperative regional anesthesia/analgesia during mastectomy for breast cancer with a decreased incidence of cancer recurrence. However, to date, no prospective data from a randomized controlled trial have been reported. In a previous study we found that extending a single-injection paravertebral block with a multiple-day perineural local anesthetic infusion improves analgesia. This follow-up study investigates the rates of cancer recurrence for the single-injection and multiple-day infusion treatments. METHODS: Patients undergoing unilateral (n = 24) or bilateral mastectomy (n = 36) were included in the study. All patients had been diagnosed with breast cancer or tumor in situ, except for six patients who were receiving prophylactic bilateral mastectomy and were excluded from analyses. Patients received unilateral or bilateral single-injection thoracic paravertebral block(s) corresponding to their surgical site(s) with ropivacaine and perineural catheter(s). Subsequently, patients were randomized to receive either ropivacaine 0.4% (n = 30) or normal saline (n = 30) via their catheter(s) until catheter removal on postoperative day 3. Cancer recurrence from the date of surgery until at least 2 years post surgery was investigated via chart review. RESULTS: Five of the 54 (9.2%) patients experienced a cancer recurrence following mastectomy-3 of 26 (11.5%) of the patients with perineural ropivacaine and 2 of 28 (7.1%) of the patients with perineural saline. CONCLUSIONS: This pilot study found no evidence that extending a single-injection paravertebral block with a multi-day perineural local anesthetic infusion decreases the risk of post-mastectomy cancer recurrence. However, due to the small sample size of this investigation, further research is needed to draw definitive conclusions.

Persistent postmastectomy pain and pain-related physical and emotional functioning with and without a continuous paravertebral nerve block: a prospective 1-year follow-up assessment of a randomized, triple-masked, placebo-controlled study.

BACKGROUND: In a previous randomized, triple-masked, placebo-controlled study, the authors demonstrated that extending a single-injection paravertebral nerve block with a multiple-day perineural local anesthetic infusion improves analgesia and decreases pain-related dysfunction during the 3-day infusion but not subsequent to catheter removal within 1 month after mastectomy. This report describes a prospective follow-up study of the previously published trial to investigate the possibility that extending a single-injection paravertebral block with a multiple-day infusion may decrease persistent postsurgical pain as well as pain-induced emotional and functional dysfunction 1 year after mastectomy. METHODS: Subjects undergoing uni- or bilateral mastectomy received unilateral (n = 24) or bilateral (n = 36) single-injection thoracic paravertebral block(s) with ropivacaine and perineural catheter(s). The subjects were randomized to receive either ropivacaine 0.4 % (n = 30) or normal saline (n = 30) via their catheters until the catheters were removed on postoperative day 3. Chronic pain and pain-related physical and emotional dysfunction were measured using the Brief Pain Inventory (BPI). RESULTS: No statistically significant difference between treatments 3 months after surgery was observed with the BPI. In contrast, after 12 months, only 4 subjects (13 %) who had received a perineural ropivacaine infusion reported pain-induced dysfunction compared with 14 (47 %) who had received saline infusion (P = 0.011). At 12 months, the mean BPI was 1.6 ± 4.6 for the subjects who received ropivacaine versus 5.9 ± 11.3 for the subjects who received saline (P = 0.007). CONCLUSIONS: Adding a multiple-day, continuous ropivacaine infusion to a single-injection ropivacaine paravertebral nerve block may result in a lower incidence of pain as well as pain-related physical and emotional dysfunction 1 year after mastectomy.

Treatment of postmastectomy pain with ambulatory continuous paravertebral nerve blocks: a randomized, triple-masked, placebo-controlled study.

BACKGROUND: We aimed to determine with this randomized, triple-masked, placebo-controlled study if benefits are afforded by adding a multiple-day, ambulatory, continuous ropivacaine paravertebral nerve block to a single-injection ropivacaine paravertebral block after mastectomy. METHODS: Preoperatively, 60 subjects undergoing unilateral (n = 24) or bilateral (n = 36) mastectomy received either unilateral or bilateral paravertebral perineural catheter(s), respectively, inserted between the third and fourth thoracic transverse process(es). All subjects received an initial bolus of ropivacaine 0.5% (15 mL) via the catheter(s). Subjects were randomized to receive either perineural ropivacaine 0.4% or normal saline using portable infusion pump(s) [5 mL/h basal; 300 mL reservoir(s)]. Subjects remained hospitalized for at least 1 night and were subsequently discharged home where the catheter(s) were removed on postoperative day (POD) 3. Subjects were contacted by telephone on PODs 1, 4, 8, and 28. The primary end point was average pain (scale, 0-10) queried on POD 1. RESULTS: Average pain queried on POD 1 for subjects receiving perineural ropivacaine (n = 30) was a median (interquartile) of 2 (0-3), compared with 4 (1-5) for subjects receiving saline (n = 30; 95% confidence interval difference in medians, -4.0 to -0.3; P = 0.021]. During this same period, subjects receiving ropivacaine experienced a lower severity of breakthrough pain (5 [3-6] vs 7 [5-8]; P = 0.046) as well. As a result, subjects receiving perineural ropivacaine experienced less pain-induced physical and emotional dysfunction, as measured with the Brief Pain Inventory (lower score = less dysfunction): 14 (4-37) versus 57 (8-67) for subjects receiving perineural saline (P = 0.012). For the subscale that measures the degree of interference of pain on 7 domains, such as general activity and relationships, subjects receiving perineural saline reported a median score 10 times higher (more dysfunction) than those receiving ropivacaine (3 [0-24] vs 33 [0-44]; P = 0.035). In contrast, after infusion discontinuation, there were no statistically significant differences detected between treatment groups. CONCLUSIONS: After mastectomy, adding a multiple-day, ambulatory, continuous ropivacaine infusion to a single-injection ropivacaine paravertebral nerve block results in improved analgesia and less functional deficit during the infusion. However, no benefits were identified after infusion discontinuation.

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.

Continuous femoral nerve blocks: the impact of catheter tip location relative to the femoral nerve (anterior versus posterior) on quadriceps weakness and cutaneous sensory block.

BACKGROUND: During a continuous femoral nerve block, the influence of catheter tip position relative to the femoral nerve on infusion characteristics remains unknown. METHODS: We inserted bilateral femoral perineural catheters in volunteers (ultrasound-guided, needle in-plane). Subjects' dominant side was randomized to have the catheter tip placed either anterior or posterior to the femoral nerve. The contralateral limb received the alternative position. Ropivacaine 0.1% was administered through both catheters concurrently for 6 hours (4 mL/h). Outcome measures included the maximum voluntary isometric contraction (MVIC) of the quadriceps femoris muscle and tolerance to cutaneous electrical current over to the distal quadriceps tendon. Measurements were performed at hour 0 (baseline), and on the hour until hour 9, as well as hour 22. The primary end point was the MVIC of the quadriceps at hour 6. RESULTS: As a percentage of the baseline measurement, quadriceps MVIC for limbs with anterior (n = 16) and posterior (n = 16) catheter tip placement did not differ to a statistically significant degree at hour 6 (mean [SD] 29% [26] vs 30% [28], respectively; 95% confidence interval: -22% to 20%; P = 0.931), or at any other time point. However, the maximum tolerance to cutaneous electrical current was higher in limbs with anterior compared with posterior catheter tip placement at hour 6 (20 [23] mA vs 6 [4] mA, respectively; 95% confidence interval: 1-27 mA; P = 0.035), as well as at hours 1, 7, 8, and 9 (P < 0.04). CONCLUSIONS: This study documents the significant (70%-80%) quadriceps femoris weakness induced by a continuous femoral nerve block infusion at a relatively low dose of ropivacaine (4 mg/h) delivered through a perineural catheter located both anterior and posterior to the femoral nerve. In contrast, an anterior placement increases cutaneous sensory block compared with a posterior insertion, without a concurrent relative increase in motor block.

Ultrasound-guided (needle-in-plane) perineural catheter insertion: the effect of catheter-insertion distance on postoperative analgesia.

BACKGROUND: When using ultrasound guidance to place a perineural catheter for a continuous peripheral nerve block, keeping the needle in plane and nerve in short axis results in a perpendicular needle-to-nerve orientation. Many have opined that when placing a perineural catheter via the needle, the acute angle may result in the catheter bypassing the target nerve when advanced beyond the needle tip. Theoretically, greater catheter tip-to-nerve distances result in less local anesthetic-to-nerve contact during the subsequent perineural infusion, leading to inferior analgesia. Although a potential solution may appear obvious-advancing the catheter tip only to the tip of the needle, leaving the catheter tip at the target nerve-this technique has not been prospectively evaluated. We therefore hypothesized that during needle in-plane ultrasound-guided perineural catheter placement, inserting the catheter a minimum distance (0-1 cm) past the needle tip is associated with improved postoperative analgesia compared with inserting the catheter a more traditional 5 to 6 cm past the needle tip. METHODS: Preoperatively, subjects received a popliteal-sciatic perineural catheter for foot or ankle surgery using ultrasound guidance exclusively. Subjects were randomly assigned to have a single-orifice, flexible catheter inserted either 0 to 1 cm (n = 50) or 5 to 6 cm (n = 50) past the needle tip. All subjects received a single-injection mepivacaine (40 mL of 1.5% with epinephrine) nerve block via the needle, followed by catheter insertion and a ropivacaine 0.2% infusion (basal 6 mL/hr, bolus 4 mL, 30-min lockout), through at least the day after surgery. The primary end point was the average surgical pain as measured with a 0- to 10-point numeric rating scale the day after surgery. Secondary end points included time for catheter insertion, incidence of catheter dislodgement, maximum ("worst") pain scores, opioid requirements, fluid leakage at the catheter site, and the subjective degree of an insensate extremity. RESULTS: Average pain scores the day after surgery for subjects of the 0- to 1-cm group were a median of 2.5 (interquartile range, 0.0-5.0), compared with 2.0 (interquartile range, 0.0-4.0) for subjects of the 5- to 6-cm group (P = 0.42). Similarly, among the secondary end points, no statistically significant differences were found between the 2 treatment groups. There was a trend of more catheter dislodgements in the minimum-insertion group (5 vs 1; P = 0.20). CONCLUSIONS: This study did not find evidence to support the hypothesis that, for popliteal-sciatic perineural catheters placed using ultrasound guidance and a needle-in-plane technique, inserting the catheter a minimum distance (0-1 cm) past the needle tip improves (or worsens) postoperative analgesia compared with inserting the catheter a more traditional distance (5-6 cm). Caution is warranted if extrapolating these results to other catheter designs, ultrasound approaches, or anatomic insertion sites.

Continuous femoral versus posterior lumbar plexus nerve blocks for analgesia after hip arthroplasty: a randomized, controlled study.

BACKGROUND: Hip arthroplasty frequently requires potent postoperative analgesia, often provided with an epidural or posterior lumbar plexus local anesthetic infusion. However, American Society of Regional Anesthesia guidelines now recommend against epidural and continuous posterior lumbar plexus blocks during administration of various perioperative anticoagulants often administered after hip arthroplasty. A continuous femoral nerve block is a possible analgesic alternative, but whether it provides comparable analgesia to a continuous posterior lumbar plexus block after hip arthroplasty remains unclear. We therefore tested the hypothesis that differing the catheter insertion site (femoral versus posterior lumbar plexus) after hip arthroplasty has no impact on postoperative analgesia. METHODS: Preoperatively, subjects undergoing hip arthroplasty were randomly assigned to receive either a femoral or a posterior lumbar plexus stimulating catheter inserted 5 to 15 cm or 0 to 1 cm past the needle tip, respectively. Postoperatively, patients received perineural ropivacaine, 0.2% (basal 6 mL/hr, bolus 4 mL, 30-minute lockout) for at least 2 days. The primary end point was the average daily pain scores as measured with a numeric rating scale (0-10) recorded in the 24-hour period beginning at 07:30 the morning after surgery, excluding twice-daily physical therapy sessions. Secondary end points included pain during physical therapy, ambulatory distance, and supplemental analgesic requirements during the same 24-hour period, as well as satisfaction with analgesia during hospitalization. RESULTS: The mean (SD) pain scores for subjects receiving a femoral infusion (n = 25) were 3.6 (1.8) versus 3.5 (1.8) for patients receiving a posterior lumbar plexus infusion (n = 22), resulting in a group difference of 0.1 (95% confidence interval -0.9 to 1.2; P = 0.78). Because the confidence interval was within a prespecified -1.6 to 1.6 range, we conclude that the effect of the 2 analgesic techniques on postoperative pain was equivalent. Similarly, we detected no differences between the 2 treatments with respect to the secondary end points, with one exception: subjects with a femoral catheter ambulated a median (10th-90th percentiles) 2 (0-17) m the morning after surgery, in comparison with 11 (0-31) m for subjects with a posterior lumbar plexus catheter (data nonparametric; P = 0.02). CONCLUSIONS: After hip arthroplasty, a continuous femoral nerve block is an acceptable analgesic alternative to a continuous posterior lumbar plexus block when using a stimulating perineural catheter. However, early ambulatory ability suffers with a femoral infusion.

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.