Comparison of Procedural Times for Ultrasound-Guided Perineural Catheter Insertion in Obese and Nonobese Patients

Transcription

1 ORIGINAL RESEARCH Comparison of Procedural Times for Ultrasound-Guided Perineural Catheter Insertion in Obese and Nonobese Patients Edward R. Mariano, MD, MAS, Jay B. Brodsky, MD Article includes CME test Received March 14, 2011, from the Department of Anesthesia, University of California, San Diego, California USA; and Department of Anesthesia, Stanford University School of Medicine, Stanford, California USA. Revision requested April 8, Revised manuscript accepted for publication April 20, We thank Brian M. Ilfeld, MD, MS (University of California, San Diego), for invaluable editorial assistance and guidance during manuscript preparation. This project was support by the Departments of Anesthesiology, University of California, San Diego, and Stanford University School of Medicine, and the VA Palo Alto Health Care System (Palo Alto, CA). The contents of this article are solely the responsibility of the authors and do not necessarily represent the official views of these entities. Dr Mariano has received funding for other research investigations from Teleflex Medical (Research Triangle Park, NC) and Stryker Instruments (Kalamazoo, MI, USA) and previously conducted continuous peripheral nerve block workshops for Stryker Instruments. These companies had no input into any aspect of this study s 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 BMI, body mass index Objectives Perineural catheter insertion with ultrasound guidance alone has been described, but it remains unknown whether this new technique results in the same procedural time and success rate for obese and nonobese patients. We therefore tested the hypothesis that obese patients require more time for perineural catheter insertion compared to nonobese patients despite using ultrasound. Methods Data from 5 previously published randomized clinical trials comparing ultrasound- and stimulation-guided perineural catheter insertion techniques were reviewed, and patients who received ultrasound-guided catheters were divided into 2 groups: obese (body mass index 30 kg/m 2 ) and nonobese (body mass index <30 kg/m 2 ). A standardized ultrasound-guided nonstimulating catheter technique was used with mepivacaine, 1.5% (40 ml), as the initial bolus via the placement needle for the primary surgical nerve block. The primary outcome was the procedural time for perineural catheter insertion. Secondary outcomes included block efficacy, procedure-related pain, fluid leakage, vascular puncture, and catheter dislodgment. Results A sample of 120 patients was identified: 51 obese and 69 nonobese. All obese patients had successful catheter placement compared to 68 of 69 (98%) nonobese patients (P =.388). The time for perineural catheter insertion [median (10th 90th percentiles)] was 7 (4 12) minutes for obese patients versus 7 (4 15) minutes for nonobese patients (P =.732). There were no statistically significant differences in other secondary outcomes. Conclusions On the basis of this retrospective analysis, perineural catheter insertion is not prolonged in obese patients compared to nonobese patients when an ultrasoundguided technique is used. However, these results are only suggestive and require confirmation through prospective study. Key Words continuous peripheral nerve block; obesity; perineural catheter; ultrasound-guided regional anesthesia Obese patients presenting for eligible surgery may benefit considerably from regional anesthesia techniques because of their often difficult airways and increased sensitivities to anesthetic agents, muscle relaxants, and opioids. 1 Unfortunately, obesity is associated with technical difficulty in the performance of regional anesthesia procedures 2 as well as higher failure rates compared to nonobese patients. 3 Although the use of surface ultrasound guidance has been explored in the obese patient population for neuraxial blockade, 4,5 the effectiveness of ultrasound guidance for peri neural catheter insertion in the setting of obesity has not been explored to date by the American Institute of Ultrasound in Medicine J Ultrasound Med 2011; 30:

2 There has been increasing interest in placement techniques for perineural catheters using ultrasound guidance in recent years. 6 8 Compared to the traditional stimulating catheter technique, an exclusively ultrasound-guided approach results in high success rates for catheter insertion and reduces the procedural time However, it remains unknown whether this new ultrasound-guided technique results in the same procedural time and success rate in obese compared to non-obese patients. We therefore performed a pooled analysis of previously published clinical trial data to test the hypothesis that obese patients require more time for perineural catheter insertion compared to nonobese patients despite using an ultrasound-guided technique. Materials and Methods The Institutional Review Board (University of California, San Diego School of Medicine) reviewed the research plan and granted written exemption from Institutional Review Board approval. Prospectively gathered deindentified data from 5 previously published randomized clinical trials comparing ultrasound- and stimulation-guided perineural catheter insertion techniques 9 13 were reviewed. Data from the cohort of patients who underwent preoperative perineural catheter insertion using ultrasound alone were then divided into 2 groups: obese (body mass index [BMI] 30 kg/m 2 ) and nonobese (BMI <30 kg/m 2 ). During the original randomized clinical trials, each study patient received a nonstimulating perineural catheter using a standardized ultrasound-guided technique as previously described Review of the Catheter Insertion Technique Following standard American Society of Anesthesiologists monitoring guidelines and titration of intravenous sedatives, the procedural area was cleansed with chlorhexidine gluconate and isopropyl alcohol (ChloraPrep One-Step; Medi-Flex Hospital Products, Inc, Overland Park, KS), and a clear, sterile, fenestrated drape was applied. With the ultrasound transducer appropriate for the desired perineural catheter site (MicroMaxx; SonoSite, Inc, Bothell, WA) in a sterile sleeve, the target nerve was identified in a transverse cross-sectional view. Once the optimal image of the target nerve was obtained, a local anesthetic skin wheal was raised next to the ultrasound transducer. An 8.9-cm, 17-gauge Tuohy-tip needle (FlexTip; Arrow International, Reading, PA) was inserted through the skin wheal in plane beneath the ultrasound transducer and directed toward the target nerve. With the needle properly positioned, a local anesthetic solution (40 ml of mepivacaine, 1.5%, with epinephrine, μg/ml) was injected in divided doses circumferentially around the target nerve via the needle. A 19-gauge catheter (FlexTip; Arrow International) was then placed through the length of the needle and advanced 5 cm beyond the needle tip. Once a catheter had been inserted, the needle itself was withdrawn over the catheter. The injection port was attached to the end of the catheter, and the catheter tip position was inferred by injecting 1 ml of air via the catheter under ultrasound guidance, slightly withdrawn if necessary, and another 1 ml of air was injected to confirm accurate catheter tip placement. 14 The catheter was not tunneled farther but was dressed and secured with an anchoring device (StatLock; Venetec International, San Diego, CA). All catheters were placed by an attending physician with extensive experience in the ultrasound-guided technique or a regional anesthesia fellow or resident under the direct one-on-one supervision of the attending physician. Postoperatively, the patients were discharged with an portable electronic infusion pump (Pain Pump 2 Block- Aid; Stryker Instruments, Kalamazoo, MI) connected to the perineural catheter and programmed to deliver 0.2% ropivacaine (basal rate of 8 ml/h, patient-controlled bolus of 4 ml, and lockout interval of 30 minute). The patients were prescribed an oral opioid (5-mg oxycodone tablets) for breakthrough postoperative pain inadequately treated by the perineural ropivacaine infusion/bolus. Outcome Measurements The primary outcome was the procedural time for perineural catheter insertion in minutes starting when the ultrasound transducer first touched the patient and ending when the placement needle was withdrawn after catheter deployment. Secondary outcomes included block efficacy and procedure-related pain on a numeric rating scale of 0 to 10 (0, no discomfort; and 10, worst discomfort imaginable) immediately after catheter placement and fluid leakage, vascular puncture, and catheter dislodgment reported on postoperative day 1. Statistical Analysis Normality of distribution was determined using the Kolmogorov-Smirnov test (NCSS Statistical Software, Kaysville, UT). For normally distributed data, comparisons of independent samples were performed using the Student t test. For continuous data in distributions other than normal, the Mann-Whitney U test was used. Simple linear regression was performed to further analyze the as J Ultrasound Med 2011; 30:

3 sociation, if any, between the BMI and procedural time. The z test or Fisher exact test (n < 5 in any category) were used for comparisons of categorical variables. Two-sided P <.05 was considered statistically significant for the primary outcome. Because this study was a retrospective analysis of an existing data set, a post hoc calculation was performed to determine the power of the study to detect a 5-minute difference between groups (NCSS Statistical Software). Results From the original data set consisting of 240 patients who participated in previous randomized clinical trials, 9 13 a sample of 120 patients meeting study criteria (ie, catheters inserted using ultrasound guidance) was identified: 51 obese and 69 nonobese. Demographic, anthropometric, and catheter site data are presented in Table 1. Of note, obese patients were older [median (10th 90th percentiles)] versus nonobese patients [54 (30 68) and 45 (21 70), respectively; P =.035]. All obese patients had successful catheter placement per the protocol 9 13 compared to 68 of 69 (98%) nonobese patients (P=.388). The 1 patient who had a misplaced catheter was a 32-year-old man (BMI, 28 kg/m 2 ) who underwent ankle arthroscopy and had received a popliteal-sciatic perineural catheter preoperatively for postoperative analgesia. Despite reporting lack of cold sensation in the affected extremity before surgery, the patient had severe pain after emergence from general anesthesia with no evidence of sciatic nerve anesthesia despite a subsequent catheter bolus. The poplitealsciatic perineural catheter was replaced successfully in the postanesthesia care unit using ultrasound guidance. Primary Outcome The time for perineural catheter insertion [median (10th 90th percentiles)] was 7 (4 12) minutes for obese patients versus 7 (4 15) minutes for nonobese patients (P =.732). A post hoc power analysis was performed, and based on the sample size and prior assumptions (α =.05 and 5- minute SD from previously published study data), the present analysis had greater than 99.9% power to detect a 5-minute difference between groups. Secondary Outcomes A linear relationship did not exist between the BMI and procedural time (R 2 = 0.004). Procedure-related catheter insertion pain was similar for obese and nonobese patients [1 (0 4) versus 1 (0 4), respectively; P =.519]. There were no statistically significant differences in other secondary outcomes (Table 2). Table 1. Population Data and Procedural Information Obese Nonobese Characteristic (n = 51) (n = 69) P Age, y 54 (30 68) 45 (21 70).035 Sex, female/male 28/23 42/ Body mass index, kg/m 2 33 (30 41) 24 (21 28) <.001 Catheter insertion site Femoral Infraclavicular Interscalene Popliteal Values are reported as median (10th 90th percentiles) or number of patients, as indicated. Discussion When using the exclusively ultrasound-guided technique described in this study, perineural catheter insertion may be performed in the same amount of time and result in the same success rate for obese and nonobese patients. To our knowledge, a study evaluating the efficacy or efficiency of ultrasound-guided perineural catheter insertion specifically in obese patients has not been reported previously. The results of this study are specific to the technique and equipment used and cannot be extrapolated to other ultrasound-guided perineural catheter insertion techniques. For example, the technique used in this study relies on in-plane needle guidance and the insertion of a flexible epidural-type catheter to avoid bypassing the target nerve Other ultrasound-guided perineural catheter techniques incorporating less-flexible catheters use out-ofplane needle guidance to facilitate a needle approach that is nearly parallel to the target nerve. 6,15,16 The purpose of this study was not to compare various ultrasound-guided perineural catheter techniques. Therefore, we cannot draw conclusions regarding how well or poorly these alternative ultrasound-guided perineural catheter insertion techniques will compare to our technique in obese patients. Future research to determine the optimal ultrasound-guided perineural catheter equipment and insertion technique for obese and nonobese patients is warranted. Table 2. Secondary Outcomes Obese Nonobese Age, y (n = 51) (n = 69) P Fluid leakage at site Vascular puncture Catheter dislodged Values are reported as number of patients. J Ultrasound Med 2011; 30:

4 Catheter Placement Time The lack of a statistically significant difference in the catheter insertion time or success rate between obese and nonobese patients is in contrast to the results of a study by Nielsen and colleagues. 3 In that study, peripheral nerve blocks were placed without the aid of ultrasound guidance. Although it is tempting to speculate that ultrasound guidance is superior to traditional nerve localization techniques in obese patients, this theory is unproven currently and requires confirmation in randomized clinical trials. It is worth noting that 100% of the ultrasound-guided perineural catheters were placed successfully in the obese group, and 90% of the patients completed catheter insertion in 12 minutes or less. The time measurement in this study did not include setup time for the catheter and ultrasound equipment because this time was considered equal between the study groups. Combined Ultrasound Nerve Stimulation We elected to study a perineural catheter insertion technique relying exclusively on ultrasound guidance even though a combined technique may offer additional benefits over either technique alone Arguably, electrical stimulation may aid the practitioner in localizing a target nerve when the sonographic anatomy is difficult to discern, especially in the morbidly obese. At present, however, there is no clear evidence that electrical stimulation offers any additional benefit when combined with ultrasound guidance It is possible that stimulating perineural catheters may have an analgesic advantage over nonstimulating catheters, 13 but the ultrasound-guided stimulating perineural catheter placement technique 17,25 remains unproven in randomized clinical trials against perineural catheter insertion methods relying exclusively on ultrasound guidance or electrical stimulation. Study Limitations Although the data included in this analysis were gathered prospectively, 9 13 the study was retrospective in nature nonetheless and subject to sources of bias similar to other retrospective studies. Even if this study yielded statistically significant findings, confirmation by a prospective trial would be necessary before considering the results definitive. 26 Furthermore, failure to demonstrate the superiority of one technique over another is not proof of equivalency. Because this study was not a randomized clinical trial, the resulting group numbers was unbalanced, and the median age of the obese group was found to be older than that of the nonobese group. We do not believe that either of these factors influenced the results of the study. On the basis of the post hoc power analysis, our study had greater than 99.9% power to detect the anticipated difference between groups given the actual number of patients. We acknowledge the limited generalizability of the study given that the results apply specifically to the technique and associated equipment included in this investigation. Another potential limitation was that trainees placed nearly all of the perineural catheters included in this study, a factor that may also limit the generalizability of the results. Conclusions In summary, the results of this retrospective study do not show a statistically significant difference in the perineural catheter insertion time or success rate for obese patients compared to nonobese patients when an exclusively ultrasound-guided technique is used. These results do not necessarily apply to all ultrasound-guided perineural catheter insertion techniques or equipment. References 1. Casati A, Putzu M. Anesthesia in the obese patient: pharmacokinetic considerations. J Clin Anesth 2005; 17: Ranta P, Jouppila P, Spalding M, Jouppila R. The effect of maternal obesity on labour and labour pain. 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