Given the current opioid epidemic

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1 TECHNICAL INNOVATION Comparative Echogenicity of an Epidural Catheter and 2 New Catheters Designed for Ultrasound-Guided Continuous Peripheral Nerve Blocks Daniel M. Moy, MD, T. Edward Kim, MD, T. Kyle Harrison, MD, Jody C. Leng, MD, Brendan Carvalho, MB, BCh, FRCA, Steven K. Howard, MD, Cynthia Shum, DNP, MEd, RN, CHSE-A, Alex Kou, BS, Edward R. Mariano, MD, MAS, Anesthesiology-Directed Advanced Procedural Training (ADAPT) Research Group Received January 20, 2017, from the Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University School of Medicine, Stanford, California USA (D.M.M., T.E.K., T.K.H., J.C.L., B.C., S.K.H., A.K., E.R.M.); and Anesthesiology and Perioperative Care Service, VA Palo Alto Health Care System, Palo Alto, California USA (T.E.K., T.K.H., J.C.L., S.K.H., C.S., A.K., E.R.M.). Manuscript accepted for publication March 6, Dr Carvalho is a consultant for Smiths Medical (St Paul, MN) and Pacira Pharmaceuticals Inc (Parsippany, NJ) and has received research funding from Covidien-Medtronic (Minneapolis, MN). Dr Mariano has received unrestricted funding for educational programs paid to his institution from Halyard Health (Alpharetta, GA) and B. Braun (Bethlehem, PA). These companies had absolutely no input into any aspect of the present study conceptualization, design, and implementation; data collection, analysis, and interpretation; or manuscript preparation. Address correspondence to Edward R. Mariano, MD, MAS, Anesthesiology and Perioperative Care Service, VA Palo Alto Health Care System, 3801 Miranda Ave, 112A, Palo Alto, CA USA. emariano@stanford.edu Abbreviations ICC, intraclass correlation coefficient doi: /jum Visualization of the catheter during ultrasound-guided continuous nerve block performance may be difficult but is an essential skill for regional anesthesiologists. The objective of this in vitro study was to evaluate 2 newer catheters designed for enhanced echogenicity and compare them to a widely used catheter not purposely designed for ultrasound guidance. Outcomes were the numbers of first-place rankings among all 3 catheters and scores on individual echogenicity criteria as assessed by 2 blinded reviewers. Catheters designed for echogenicity are not superior to an older regional anesthesia catheter, and results suggest that catheter preference for ultrasound-guided placement may be subjective. Key Words continuous peripheral nerve block catheter; echogenicity; perineural catheter; ultrasound; ultrasound-guided regional anesthesia Given the current opioid epidemic 1 and association between surgery and long-term opioid use, 2,3 it is more important than ever to maximize the use of nonopioid analgesic techniques to manage pain. A continuous peripheral nerve block provides targeted delivery of a local anesthetic directly to a nerve or plexus via a perineural catheter. 4 For a continuous peripheral nerve block to be effective, precise catheter placement is essential, and evidence supports ultrasound imaging as the preferred method for catheter insertion. 5,6 Since catheters were used for continuous peripheral nerve blocks before the advent of ultrasound-guided regional anesthesia, 7 echogenic technology to enhance catheter visibility under ultrasound guidance is a relatively recent innovation. Few studies to date have evaluated the echogenicity of perineural catheters, 8 10 and newer products are now approved and available commercially. We designed this study to compare the echogenic characteristics of 2 new catheters designed specifically to enhance echogenicity for ultrasound-guided continuous peripheral nerve block to an older established catheter used commonly in regional anesthesia. Materials and Methods TheAnimalUseCommittee(ResearchAdministration,VAPalo Alto Health Care System) approved the study protocol. VC 2017 by the American Institute of Ultrasound in Medicine J Ultrasound Med 2017; 36:

2 Experimental Design Similar to previous studies, we used a meat phantom model consisting of pork shoulder specimens with bovine tendon inserted to simulate a target nerve. 8,11 13 We tested 3 commercially available catheters used for regional anesthesia (Figure 1): the established 19- gauge single-orifice Arrow FlexTip Plus epidural catheter (Teleflex Medical, Research Triangle Park, NC), which is reinforced with an internal metal coil ; the new 20-gauge single-orifice Contiplex ECHO catheter with integrated flat metal coils throughout its length (B. Braun Medical, Inc, Bethlehem, PA); and the newly approved 21-gauge single-orifice Ultra-Kath catheter (Epimed International, Inc, Johnstown, NY), which has twin braided internal metal wires and was previously studied before approval by the US Food and Drug Administration. 8 Each catheter was tested 18 times for a total convenience sample of 54 trials. A stratified randomization sequence was generated by using a computer-generated randomization table ( The study used 6 prepared meat phantom specimens, with 9 catheter insertions performed per specimen and each of the 3 catheter types assigned randomly in balanced proportions. A single investigator (T.E.K.) with expertise in ultrasound-guidedregionalanesthesiaplacedeachcatheter at a 458 angle to the surface using an ultrasoundguided short-axis in-plane technique 8,17 via the Tuohytip placement needle accompanying each catheter. A new insertion site was used for each catheter trial. Each placement needle was inserted at a distance of approximately 5 cm and in contact with the simulated target nerve. Catheters placed in this experiment were only inserted to the end of the needle and not farther; then the placement needle was withdrawn over the catheter, leaving the catheter in place. Catheters were not advanced beyond the needle tip, and additional catheter length was not inserted within the tissue layers superficial to the target. The same ultrasound settings were used for catheter insertion and subsequent image capture and were not altered during the study: a highfrequency (15 6 MHz) ultrasound transducer (M- Turbo HFL50; Fujifilm SonoSite, Inc, Bothell, WA) with a 3.3-cm depth and a nerve preset examination with all factory default settings specific to this examination. Catheter insertion sites were marked with a pin, and exposed catheters were covered with a towel. A blinded evaluator (T.K.H.) then scanned each inserted catheter using the same ultrasound transducer and examination settings that were used for initial placement. Ultrasound images were saved under coded file names. Outcomes The primary outcome was the percentage that a catheter image was ranked best for ultrasound visualization among the 3 different catheters. For this outcome, catheter images were randomly clustered into 18 sets of 3, with each set including a single image of each catheter type. Within each cluster, blinded reviewers (J.C.L. and B.C.) ranked the 3 images based on visualization of the catheter (1, highest score; 3, lowest score). Secondary outcomes were scanning time (seconds from transducer contact until the best image of the catheter acquired), estimated percentage of the catheter length visualized, and echogenicity scores (Table 1) adapted for catheters 8 from the needle echogenicity study by Maecken et al. 18 The scores for echogenicity were rated separately for each image (not in clusters as for the primary outcome) by the same blinded reviewers using an 11-point Likerttypescale(Table1).Thecatheterlengthvisualizedand echogenicity scores were assessed by 2 blinded reviewers using Windows Photo Viewer (Microsoft Corporation, Redmond, WA); these reviewers were not involved in anyotherstudyprocedures. Figure 1. Gross images and sample sonograms showing the 3 catheters studied: A, Arrow FlexTip Plus; B, Contiplex ECHO; and C, Ultra-Kath. Arrowheads indicate distal end of catheter; and T, simulated target nerve J Ultrasound Med 2017; 36:

3 Sample Size Estimate No a priori sample size estimate was performed. A convenience sample of 54 was used, based on the availability of 6 custom-prepared meat phantoms and 3 catheter types. Fifty-four trials allowed for 18 total scans per catheter type and stratified randomization of 9 trials balanced among the 3 catheter types per meat phantom. Investigators of a previously published study of catheter echogenicity performed 15 trials per catheter. 8 Statistical Analyses Experimental analyses were conducted in the R version statistical programming language (R Foundation for Statistical Computing, Vienna, Austria). The normal distribution was determined by the Shapiro-Wilk normality test. Proportions of best rankings for each catheter type were compared by the Pearson v 2 test. Echogenicity scores were evaluated across catheter types by the Kruskal-Wallis test and post hoc pair-wise Wilcoxon rank sum tests with Holm P value adjustment between catheter types. The scanning time to acquire the best image of each catheter was compared by survival analysis with the log rank test. Two-sided P <.05 was considered statistically-significant. To assess the reliability of echogenicity scores between the 2 blinded reviewers, intraclass correlation coefficients (ICCs) 19 were calculated. We interpreted ICCs as follows: fair for values of 0.40 to 0.59, good for values of 0.60 to 0.74, and excellent for values of greater than Results All catheters were inserted per the protocol; 1 catheter was accidentally dislodged after insertion but before image acquisition, so it was replaced as assigned. There was no difference in the time to image acquisition [median (10th 90th percentiles)] among the 3 catheter types: 24.3 ( ) seconds for Arrow, 14.7 ( ) seconds for Contiplex ECHO, and 17.9 ( ) seconds for Ultra-Kath (P 5.831). The Contiplex ECHO catheter was ranked best for ultrasound visibility: 17 of 36 times (47%) compared to 13 of 36 (36%) for Arrow and 6 of 36 (17%) for Ultra- Kath; there was no difference between Arrow and Contiplex ECHO (P 5.473) or between Arrow and Ultra- Kath (P 5.217), but there was a difference between Contiplex ECHO and Ultra-Kath (P 5.034). Overall, there were no differences in echogenic characteristics among the 3 catheter types (Table 2). We did observe differences in inter-rater reliability among the individual characteristics scored. The ICC values (95% confidence intervals) were ( ) for visibility, ( ) for artifact, ( ) for shadowing, ( ) for contrast, and ( ) for catheter length seen. Given these ICC values, subanalyses were conducted on the echogenicity scores for each reviewer individually. Scores from the first reviewer showed a difference in artifact [median (10th 90th percentiles)] favoring Arrow [4 (2 6)] compared to Contiplex ECHO [5 (4 8); P 5.021] and Ultra-Kath [6 (4 8); P 5.021] but no other differences between catheters in other characteristics. Scores from the second reviewer showed a difference in shadowing favoring Ultra-Kath [4 (1 8)] compared to Arrow [6 (4 9); P 5.044] but no other differences between catheters in other characteristics. Table 1. Catheter Echogenicity Characteristics and Scoring Explanations 8,18 Characteristic Description Score (0 10) Explanation Visibility Overall image quality of the catheter alone. Highest value (10) means best visibility; lowest value (0) means near invisibility. Artifact Amount and degree of artifact formation created by the catheter (eg, scattering and reverberation). Lowest value (0) is rated as best; highest value (10) is worst and is associated with marked reduction in image quality in the area surrounding the catheter. Shadowing Contrast Amount and degree of shadows created by the catheter. Distinct appearance of the catheter compared to surrounding tissue inside the model. Lowest value (0) is rated as best visibility beyond the catheter; highest score (10) describes near absence of imaging beyond the catheter. Highest value (10) means best contrast; lowest value (0) means the catheter is very difficult to identify and differentiate from its surroundings. J Ultrasound Med 2017; 36:

4 Discussion The results of this in vitro study do not show a clear advantage in favor of newer catheters designed for echogenicity when compared to an older catheter commonly used in regional anesthesia. The Contiplex ECHO catheter was ranked first for visibility most often, but this finding was only statistically significant when compared to the Ultra-Kath catheter. The Ultra-Kath catheter, whichwaspreviouslyfoundtobesuperiorto3other catheters in terms of echogenicity, 8 was least likely to be ranked first for ultrasound visibility in this study. There were no differences in specific echogenic characteristics among the 3 catheters, although reliability between reviewers was lacking for artifact and shadowing. This study does not confirm our previous study in which the Ultra-Kath catheter performed better than 3 other catheters used in regional anesthesia. 8 In the previous study, the 3 comparators were 2 nonechogenic regional anesthesia catheters by B. Braun (Contiplex and Perifix FX) and the Arrow StimuCath (Teleflex Medical). 8 When compared to the new Contiplex ECHO, which used echogenic technology, the Ultra-Kath loses its advantage in terms of visibility. However, this disadvantageisalsothecasewhentheultra-kathiscompared to the older Arrow FlexTip Plus epidural catheter, which was not included in the previous study. The Arrow epidural catheter, although not designed for enhanced echogenicity, has been used for ultrasound-guided continuous nerve block for more than 15 years 5 and remains widely used for ultrasound-guided regional anesthesia. The Arrow epidural catheter features an internal spring wire similar to intentionally designed echogenic catheters and is also the largest-gauge catheter among the 3 catheters evaluated. Although previous studies have examined the echogenicity of various needles used for regional anesthesia, 18 few studies have examined this topic with regard to catheters. Takatani et al 9 compared 6 catheters, including the Arrow FlexTip Plus, using a similar in vitro study design and meat phantom model. Unlike our study, they did not use a simulated target nerve and implemented a shallower 08 to 308 catheter insertion angle to optimize echogenicity. We implemented a steeper insertion angle of 458 to simulate more-difficult clinical conditions. They also did not include any catheters designed for echogenicity, and most of those included were epidural catheters rather than catheters used specifically for continuous peripheral nerve blocks. More recently, Brookes et al 10 prospectively evaluated the echogenicity and block outcomes of 78 patients undergoing total knee joint arthroplasty who received a sciatic nerve continuous peripheral nerve block with either a stimulating catheter or a nonstimulating echogenic catheter. Although their primary outcome was needle visibility, they did not find a difference in the secondary outcome of catheter tip visibility under ultrasound guidance. They ascribed the overall low percentage of catheter visibility (26.4% and 20.9% for stimulating and echogenic, respectively) to the inability to align the ultrasonic beam with the catheter in this deep block. In that study, catheters were placed with 2 different techniques: nerve stimulation was used alone for stimulating catheters, and echogenic catheters were placed with ultrasound guidance alone. Unlike our study, the injectate was administered both before catheter insertion via the placement needle and after insertion via the catheter, which may have affected ultrasound imaging. In thus study, evaluations were done by 2 reviewers, similar to our previous study. Although there were no differences found in echogenic characteristics when the reviewers scores were taken together, ICC values for inter-rater reliability were poor for 2 characteristics, artifact and shadowing, compared to the other 3 (visibility, contrast, and catheter length seen). We speculate that these 2 characteristics may be the most subjective of the Table 2. Scores for Catheter Echogenic Characteristics From Both Reviewers Characteristic Arrow (n 5 36) Contiplex ECHO (n 5 36) Ultra-Kath (n 5 36) P Visibility, (4 9) 7 (4 10) 6 (4 8).130 Artifact, (0 6) 4 (0 8) 3 (0 8).304 Shadowing, (2 9) 6 (2 8) 5 (2 8).756 Contrast, (4 9) 7 (4 9) 7 (5 8).720 Catheter length seen, % 80 (40 100) 70 (25 100) 70 (40 100).603 Values are shown as median (10th 90th percentiles) J Ultrasound Med 2017; 36:

5 group. Subanalyses of individual reviewers scores when separated show a preference for one catheter by one reviewer based on artifact and a preference for another catheter by the other reviewer based on shadowing. Although these grading criteria have been previously applied for catheters, 8 they were originally used to describe the ultrasound visibility of needles, 18 and not all of these characteristics may be as applicable to catheters. Despite the newer application of echogenic technology to catheters, to date there is no way to distinguish the shaft of the catheter from the tip, and precise placement of the tip in proximity to the target nerve or plexus is ultimately the goal of continuous peripheral nerve block mediated pain relief. 21 Therefore, other methods, suchasthe airtest maycontinuetobeusedtoinfer the catheter tip position when performing ultrasoundguided continuous peripheral nerve blocks. 22 Ultimately choice of catheter for a continuous peripheral nerve block must account for multiple factors, including but not limited to physician preference, placement technique, and cost. Limitations of our study included the use of an in vitro meat phantom model, which does not exactly mimic human tissue. The simulated target was also relatively shallow (<3 cm), which may have negated any potential advantages of echogenic technology at greater depths. However, this model has been previously described for ultrasound-guided regional anesthesia training and has been validated against human cadaver models. 23 In addition, the results of this in vitro study cannot be generalized to clinical outcomes, since echogenic characteristics and a catheter s ultrasound visibility have not been shown to correlate with analgesic efficacy or sensory blockade. The echogenic characteristics reported in this study only apply to the specific catheter insertion technique and catheter equipment used; these results should not be generalized to other catheter types or insertion techniques that have not yet been studied by the same methods. The larger gauge of the epidural catheter may have overcome the potential disadvantage of the lack echogenic technology, so the results of this study should not be extrapolated to smaller nonechogenic epidural catheters. In conclusion, results from this in vitro study demonstrate that newer catheters designed for echogenicity are not more visible under ultrasound guidance than an older and widely used epidural catheter and suggest that some aspects of catheter preference when performing ultrasound-guided regional anesthesia may be subjective and user specific. Specific elements of catheter design, such as integration of metal coils, catheter gauge, and identification of the catheter tip, may deserve further investigation when developing future catheters for ultrasound-guided regional anesthesia. References 1. Alam A, Juurlink DN. The prescription opioid epidemic: an overview for anesthesiologists. Can J Anaesth 2016; 63: Sun EC, Darnall BD, Baker LC, Mackey S. Incidence of and risk factors for chronic opioid use among opioid-naive patients in the postoperative period. JAMA Intern Med 2016; 176: Mudumbai SC, Oliva EM, Lewis ET, et al. 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