Dual Guidance. A Multimodal Approach to Nerve Location. Ralf Gebhard M.D., Admir Hadzic M.D., Ph.D., William Urmey M.D.

Transcription

1 Dual Guidance A Multimodal Approach to Nerve Location Ralf Gebhard M.D., Admir Hadzic M.D., Ph.D., William Urmey M.D. Published by B. Braun Melsungen AG

2 Dual Guidance A Multimodal Approach to Nerve Location Ralf Gebhard M.D., Admir Hadzic M.D., Ph.D. William Urmey M.D. Published by B. Braun Melsungen AG

3 2008 B. Braun Medical Inc. All rights reserved. No part of this document may be reproduced or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission of B. Braun Medical Inc. The views expressed in this book are those of the authors only. Providers and clinicians are obligated to make their own determination of the appropriate medical treatment for each of their patients. B. Braun Medical Inc th Ave. Bethlehem, PA Printed in Germany

4 About the Authors Ralf E. Gebhard M.D. is Associate Professor in the Department of Anesthesiology and the Department of Orthopedics and Rehabilitation at the University of Miami Miller School of Medicine in Miami, Florida. He serves as the Director of the Division of Regional Anesthesia and Acute Pain Management for Jackson Memorial Hospital and the University of Miami Hospitals. Admir Hadzic M.D., Ph.D. is Director of Regional Anesthesia at St. Luke s Hospital, and Professor of Clinical Anesthesiology at the College of Physicians and Surgeons, Columbia University, New York, NY. He is American Board Certified both in Anesthesiology and Internal Medicine. Dr. Hadzic has been at the forefront of academic and clinical regional anesthesia for well over a decade and has published two best-selling textbooks in regional anesthesia. Dr Hadzic is the author of the New York School of Regional Anesthesia. William Urmey M.D. graduated from Harvard Medical School where he subsequently did his anesthesia residency and a regional fellowship at Brigham and Women s Hospital. An Associate Professor of Clinical Anesthesiology and an Associate Scientist at Hospital for Special Surgery, Weill Cornell Medical College, he has lectured and published extensively in many areas of regional anesthesia. Dr. Urmey has a long-standing interest in the science and physiology of peripheral nerve stimulation. He was the founding Editor-in-Chief of the journal, Techniques in Regional Anesthesia and Pain Management and is a member of the Board of Directors of the American Society of Regional Anesthesia.

5

6 Contents Chapter 1 Modalities of Nerve Block Performance Is there a Silver Bullet? Background and Historical Development... 3 Objectives... 4 Major Outcome Parameter - Success Rate... 4 Major Outcome Parameter - Incidence of Complications... 6 Minor Outcome Parameters - Nerve Block Onset Time and Local Anesthetic Requirements... 8 Limitations of Nerve Stimulation... 8 Limitations of Ultrasound... 9 Synergy between Nerve Stimulation and Ultrasound Conclusions Chapter 2 Dual Guidance: Integrating Nerve Stimulation and Ultrasound Background Objectives What is Dual Guidance? Redefining Our Understanding of the Nerve Nerve Stimulation, Ultrasound or Both: Which Modality Should I Use? 17 Dual Guidance in Practice: How Does It Work? Chapter 3 The Fundamentals of Nerve Stimulation Background Objectives How to Perform a Nerve Stimulation Technique (Without Ultrasound). 25 Electrophysiology of NS Important Features of Nerve Stimulators Nerve Stimulator Components Electrical Nerve Localization and Interference with EKG Monitoring Chapter 4 New Developments in Nerve Stimulation Background Objectives Transcutaneous Stimulus and Percutaneous Electrode Guidance (PEG). 37 SENS: Sequential Electrical Nerve Stimulation SENSe on the B. Braun Stimuplex HNS References... 45

7

8 Introduction Richard Brull, M.D., FRCPC The practice of regional anesthesia (RA) continues to gain popularity worldwide. Nerve localization techniques have traditionally relied upon anatomical landmarks and surrogate predictors of success. The two most commonly used techniques for nerve localization during peripheral nerve blockade (PNB) have been peripheral nerve stimulation (PNS) and mechanical elicitation of paresthesiae. Despite the time-tested safety record of these blind techniques, there remains an inherent rate of block failure and complications, including local anesthetic toxicity and nerve damage. Recently, ultrasound (US) for nerve localization has been the subject of fervent interest amongst anesthesiologists as US guidance affords real-time visualization of the needle, nerve and surrounding tissues. The anesthesiologist can thereby distribute local anesthetic uniformly around the target nerve, theoretically ensuring effective PNB. Early evidence from small randomized controlled trials suggests that US-guided PNB thus translates into faster onset, longer duration, and improved block quality with reduced amounts of local anesthetic compared to PNS. While US has arguably revolutionized the practice of RA, thoughtful consideration of four important outcomes underscores the indispensable role that PNS continues to play in modern RA practice. These outcomes are block success, complications, cost and training. Widely varying definitions of block success make comparison of published studies challenging. However, there appears to be one important underlying commonality: block success rates are similar between US and PNS when the block is performed by experts. Another proposed major advantage of US is the ability to detect inadvertent intravascular or intraneural injection. Yet, whether US ultimately enhances the safety of RA remains to be proven. Local anesthetic toxicity due to intravascular injection has already been reported despite US guidance, while large, international, multiinstitutional Retrospective Controlled Trials are required to adequately evaluate the incidence of neurological complications following US, compared to traditional nerve localization techniques. One important obstacle that continues to stifle the widespread use of US is the significant set-up cost to purchase a suitable machine. Hidden costs include additional probes, ongoing maintenance, probe covers, training and education. Cost savings may eventually be garnered through reduced block performance and onset times, as well as a reduction in complications, though the latter remains largely unproven. Finally, an increasingly indispensable advantage of US is the ability to teach trainees the clinical anatomy essential to the safe and successful PNB that would be

9 Introduction otherwise unattainable by reading textbooks, memorizing atlases or dissecting cadavers. However, needle visualization is the single biggest challenge for US trainees, and the minimum number of US-guided blocks required to achieve technical competency is unknown and likely varies with the type of block. At my home institution, we routinely utilize a dual guidance technique to guide needle tip placement, that is, US combined with adjunctive PNS in order to capitalize on the advantages and mitigate the disadvantages of each technique. We commonly employ PNS for nerve identification as US alone may not reliably confirm the identity of nerves relative to other sonographically similar structures, including adjacent nerves, tendons or blood vessels (i.e. anatomical artifacts), and the location of peripheral nerves in a given region can be highly variable between patients and even within the same patient. A dual guidance, or the use of PNS with US, technique affords the anesthesiologist an unprecedented level of understanding and respect for the heretofore mysterious needle-nerve interaction. A dual guidance technique also facilitates learning and improve trainee performance compared to teaching one technique in isolation. Most importantly, a dual guidance technique affords the anesthesiologist a higher level of confidence and comfort by drawing on two objective end points, real time visualization of local anesthetic spread and, minimum stimulating threshold current to predict the likelihood of block success and possibly, minimize block-related complications. Richard Brull, M.D., FRCPC Assistant Professor Director, Regional Anesthesia Fellowship Program Department of Anesthesia and Pain Management Toronto Western Hospital, University Health Network, University of Toronto

10 Modalities of Nerve Block Performance Is there a Silver Bullet? 1 Chapter 1 Modalities of Nerve Block Performance Is There a Silver Bullet? A review of the literature and the suggestion of a Multimodal Approach Ralf E. Gebhard M.D.

11

12 Modalities of Nerve Block Performance Is there a Silver Bullet? 3 Background and Historical Development The ideal technique to facilitate peripheral nerve block (PNB) performance would allow for rapid onset, long duration, certain success, and would eliminate complications. The search for such a technique started almost immediately once PNBs were first described. Initially performed after surgical exposure, the German physician Kulenkampf in 1911 believed that it might be advantageous to insert a needle transcutaneously and locate the nerve utilizing a paresthesia technique. 1 It was only one year later that nerve stimulation (NS) as an alternative modality was first introduced. 2 However, most likely due to the cumbersomeness of the equipment, paresthesia techniques continued to dominate as the gold standard for nerve blocks performance for several decades, best expressed and reinforced by the famous dictum by Moore, No paresthesia No anesthesia. 3 With the development of a more practical and portable nerve stimulator in and promoted by reports questioning the safety of the paresthesia technique such as by Selander in , NS slowly gained more popularity among practitioners and started to replace the paresthesia technique in a rapidly increasing fashion during the last decade of the 20th century. Contributing to this development were technical improvements in the area of NS equipment as well as the mounting evidence provided by well-conducted clinical trials regarding the significant benefits associated with peripheral nerve blocks. 6, 7, 8 It has been truthfully stated that NS allowed for the injection of science into regional anesthesia, 9 a subspecialty which was for a long time considered to be an art reserved to be practiced by artists. The influence of NS on the tremendous growth of peripheral nerve block performance observed over the last 10 years was elegantly proven by Williams et al. 10 when these authors demonstrated how NS resulted in a renewed surge in interest in regional anesthesia as indicated by the yearly growth of sales between percent of one prominent NS equipment vendor (Figure 1). Figure 1: Annual sales growth (%) increases when compared with the prior year (with 1998 as baseline) for one vendor s nerve stimulation-related products and supplies tracked over time. Also tracked are the number (n) of indexed citations of nerve block-related manuscripts describing electrical stimulation (ES) and ultrasound (US). Note that the graphic for ES citations is an order of magnitude greater than for US citations.

13 4 Modalities of Nerve Block Performance Is there a Silver Bullet? In 1989, another modality was introduced into the clinical practice. Ting and Sivagnanaratnam utilized ultrasound (US) to confirm needle placement and observe local anesthetic spread during axillary nerve blocks. 11 Over the last few years, the question whether US offers significant advantages over other aids to regional anesthesia and especially over NS has become a central issue in clinical research in the field and remains highly controversial. In a survey conducted in 2007 by the American Society of Regional Anesthesia and Pain Medicine, 12 NS still is by far the preferred technique chosen by the members of this society to PNBs (Table 1). Unfortunately, the survey did not include the frequency of combinations of different modalities utilized for nerve block performance. Table 1: Preferred modalities for nerve block performance a survey of ASRA members (Reprinted with permission and modified from Brull et al. Reg Anesth Pain Med 2008; 33: ) Objectives Of primary interest for any anesthesia provider practicing peripheral nerve blocks and for his patient is the affect that a certain modality for nerve block performance has on outcome parameters of high impact, such as success rate and/or the incidence of unwanted side effects. Of secondary importance is whether a nerve localization technique has other benefits such as faster onset or reduced local anesthetic requirement since these advantages may be of lesser clinical relevance. Consequently, this Chapter will examine and compare randomized clinical trials of NS and US to evaluate whether one modality has established superiority over the other, and recommend a strategy for the successful and safe daily practice of PNBs. Major Outcome Parameter - Success Rate A review of the literature reveals 10 prospective randomized clinical trials comparing NS and US regarding the success rate of nerve block performance. Seven trials failed to show any significant difference in success rate with three of these studies reporting a

14 Modalities of Nerve Block Performance Is there a Silver Bullet? 5 slight trend in favor of US (Table 2). Three other investigations did find a significantly improved success rate with the use of US. The first of these studies published by Chan et al. in 2007 exhibited a dramatic discrepancy between the two techniques: US guidance for axillary blocks resulted in an almost 20 percent higher success rate when compared to NS guidance. 13 However, the reported success rate for NS technique was only 63 percent, astonishingly lower than the percent success published 14, 15 previously for this technique by multiple other authors. Author Marhofer et al Williams et al Liu et al Chan et al Casati et al Perlas et al Guerkan et al Kapral et al 2008 Sauer et al 2008 Macaire et al Table 2: Approach Femoral N = 40 Supraclavicular N = 80 Axillary N = 90 Axillary N = 188 Axillary N = 60 Lateral popliteal sciatic N = 74 Infraclavicular N = 60 Interscalene N = 160 Infraclavicular N = 80 Median and Ulnar nerve at the wrist N = 60 Nerve Stimulation Success Rate Ultrasound Success Rate Statistical Significant Difference 85% 95% NO 78% 85% NO 90% 90% NO 63% 81% YES 100% 100% NO 61% 89% YES 93% 95% NO 91% 99% YES 85% 95% NO 93% 93% NO Nerve Stimulation vs. Ultrasound Nerve Block Success Rate in Randomized Clinical Trials Consequently, several editorials and letters commented on Chan s investigation, questioning the methodology. 16,17,18 The fact that Chan et al. accepted a proximal twitch (triceps) for the radial nerve response was criticized since such a response had been previously associated with a lower success rate than a distal twitch 19. Interestingly, the two other trials comparing NS and US for axillary blocks by Liu and Casati did 20, 21 not reveal the slightest difference in success rate. In 2008, Kapral et al. studied the two modalities for interscalene blocks. 22 While both techniques had high success rates, the US group was superior 99 percent as compared to the NS group with 91 percent. Similar to Chan s report, an editorial commenting on the methodology accompanied this publication. 23 Salinas et al. noted that multiple injections of local anesthetic were performed in the US group while only a single injection was executed in the NS group. Salinas stated that this is an unfair comparison, which may explain the difference in success rate.

15 6 Modalities of Nerve Block Performance Is there a Silver Bullet? Also in 2008, the same group that had reported a year earlier on the dramatic difference in success rate for the axillary block evaluated NS guidance vs. US guidance for lateral popliteal sciatic nerve blocks. 24 The latter technique was associated with a 30 percent improvement (61 percent vs. 89 percent, respectively). However, this investigation deserves some methodological criticism as well; similar to the study by Kapral et al., several injections were performed in the US group to allow for circumferential spread of local anesthetic around the nerve, whereas only one injection was performed in the NS group. Moreover, any type of distal motor response of the foot presence at a current of 0.5mA was accepted in the NS group. Previous publications had reported success rates of 88 percent with NS when a double injection technique was utilized 25 and Arcioni et al. in 2007 found a 97 percent effectiveness for a single injection NS technique as long as a tibial motor response was elicited. 26 Considering these methodological concerns with all three trials that demonstrated a significantly higher success with US when compared to NS, and the fact that such a difference was not found in seven other investigations, it appears that both methods can be equally utilized to successfully perform PNBs, especially by the experienced practitioner. Major Outcome Parameter - Incidence of Complications As stated previously, the ideal modality for nerve block performance would allow for the complete elimination of complications associated with these procedures. Overall, severe side effects are relatively rare events, but can obviously be of devastating nature for the individuals involved. Because serious complications of nerve blocks are so uncommon, prohibitively large numbers of patients are required to capture the incidence of complications and even larger numbers to investigate if different modalities result in significant differences. The biggest database so far originates from the French SOS Regional Anesthesia Hotline. 27 In more than 50,000 reported PNB procedures, only 12 cases of peripheral neuropathy and only six cases of systemic local anesthetic toxicity were observed. This tremendous safety record was achieved with NS as the technique of choice for most PNBs. The idea that visualization of the target structure, the adjacent anatomy, the nerve block needle and the spread of the local anesthetic once injected may reduce or even eliminate side effects all together seems compelling. However, recent case reports of accidental intravascular local anesthetic injection during ultrasound guided nerve blocks 28, 29 as well as case reports of nerve injury associated with the same modality 30 led to the conclusion formulated by Hadzic et al: Ultrasound may reduce but not eliminate complications of peripheral nerve blocks. 31 Nerve Injury: The incidence of severe nerve injury in a large prospective study is reported to be 2.4 in 10, There are no randomized trials comparing US vs. NS regarding the avoidance of nerve injury available in the literature. Consequently, in a recent practice advisory regarding neurological complications of regional anesthesia, the American

16 Modalities of Nerve Block Performance Is there a Silver Bullet? 7 Society of Regional Anesthesia (ASRA) stated, No nerve localization or monitoring technique has been shown to be clearly superior in terms of reducing the frequency of clinical injury. These techniques include paresthesia-seeking, peripheral NS, defined minimal or maximal milliamperage for acceptance of a motor response, US guidance, or monitoring of injection pressures. 32 The same report concluded, Peripheral nerve injury associated with regional anesthesia is likely caused by a combination of insults to the nerve s internal milieu. However, the exact sequence and relative importance of these insults remains unknown. Whether one modality, such as US by itself, will have enough impact on the combination of insults in order to reduce the incidence of nerve injury appears questionable. In addition, given the previously mentioned low overall incidence, which will require larger-sized investigations, this evidence may be extremely difficult to obtain and might never become available. Accidental Vascular Puncture: Intravascular Injections & Local Anesthetic Toxicity Unfortunately, very few studies comparing NS with US as modality for nerve block performance report on the incidence of accidental vascular puncture and no head-tohead trials are available regarding the occurrence of systemic local anesthetic toxicity. Marhofer et al. reported three accidental vascular punctures in 20 patients receiving femoral blocks with NS while no punctures occurred in 20 patients in which US was utilized. 33 However, all punctures resulted in small hematomas without the need for any further intervention. Sauter et al. described 33 percent of unintended blood aspiration with NS versus five percent occurring with US when 80 patients where randomized to receive an infraclavicular block with either technique. 34 Hematoma formation was not observed in this investigation. While it appears that accidental puncture of vascular structures occurs more frequently with NS, intravascular injections of local anesthetic resulting in systemic local anesthetic toxicity were not associated with these events nor were these reported in any other comparative trial between NS and US. The overall incidence of systemic local anesthetic toxicity varies between approximately 0.1 to 1 per thousand. The lower incidence was reported by Auroy et al. for the French SOS Regional Anesthesia Hotline 25 and may be falsely low since it relied on voluntary reporting. The higher incidence results from a retrospective chart review 35 and may be falsely elevated since the data is more than 10-years-old and does not reflect advances made in the field over the last decade. Although vessels are one of the easiest structures to identify with US, vascular punctures are not uncommon and consequently, cases of systemic toxicity have been described. 28, 29 One has to keep in mind that observing the spread of local anesthetic around a neural structure does not guarantee that the entire amount of the solution is appropriately deployed. There are no means to quantify the visualized fluid amount and smaller or even larger portions of the local anesthetic can still be injected into a blood vessel. Since only a few milliliters of local anesthetic injected intravascularly can result in systemic toxicity, 36 it is understandable that US will not be able to eliminate this potential complication completely. Whether the incidence of systemic local anesthetic toxicity is lower with US versus NS, it will need to be investigated in large randomized trials.

17 8 Modalities of Nerve Block Performance Is there a Silver Bullet? Minor Outcome Parameters - Nerve Block Onset Time and Local Anesthetic Requirements In two different investigations, Marhofer et al. reported 11 min. and 13 min. faster onset of US-guided femoral nerve blocks vs. NS-guided nerve blocks. 33, 37 The same group observed a 6 min. shortened onset of infraclavicular blocks in children with the use of US. 38 Axillary block onset was reportedly hastened by 4 min. by US, 21 while Sauter et al. did not find any difference between US and NS regarding onset time of infraclavicular blocks. 34 For wrist blocks, Macaire et al. described a 2 min. faster onset with the NS technique. 39 Whether any of these results are of significant clinical importance will largely depend on the practice circumstances and habits of each individual anesthesiologist. For example, when blocks are performed outside the operating room in a separate block room in advance of surgery, a few minutes difference in onset time may have a lesser impact compared to a setting in which patients are blocked in the operating room immediately prior to the case. Several studies have compared the required local anesthetic volume to perform a femoral nerve block with either NS or US guidance. The best-designed trial by Casati et al. utilized an up-and-down staircase methodology to determine the effective dose in 95 percent of cases (ED95). 40 US guidance resulted in a 42 percent reduction of local anesthetic requirements compared to NS (22ml vs. 41ml, respectively). Similarly, to the impact on success rate, this apparent disadvantage of NS can be overcome by performing multiple injections. By utilizing the same study methodology, Casati et al. had previously reported an ED95 of 21ml for a multiple injection NS-guided femoral nerve block, while 29ml where necessary with a single injection technique. 41 Limitations of Nerve Stimulation Recently, NS has been associated with a low sensitivity for detection of needle to nerve contact. Urmey et al. reported only a 30 percent presence of motor response with stimulating currents up to 1mA after eliciting paresthesia in unsedated patients undergoing interscalene blocks. 42 Choyce et al. found that motor response at 0.5mA or less occurred in 77 percent of patients in whom a paresthesia had been provoked during axillary blocks. 43 These reports have resulted in a heated debate regarding their clinical value with critics arguing that most patients will exhibit some sort of voluntary or involuntary movement as reaction to a paresthesia. 44 Such a reaction could consequently affect the position of the nerve block needle and explain the lack of motor response observed by Urmey and Choyce. Interestingly, a significantly higher sensitivity for needle to nerve contact for NS compared to paresthesia with 75 percent vs. only 38 percent reported when US was used as a reference test for needle-to-nerve contact during axillary blocks. 45 Whether it is really acceptable to utilize US as a gold standard to evaluate other nerve block modalities with regards to needle positioning

18 Modalities of Nerve Block Performance Is there a Silver Bullet? 9 can be discussed controversially since US also has limitations (see below). Another investigation, which used US as a reference to evaluate motor response sensitivity during interscalene block, did find a wide range of current associated with a motor response once a needle was placed under US guidance. While a motor response was found in 100 percent of cases, the necessary current was at or below 0.5mA in 42 percent of patients, and ranged from above 0.5mA to 1.7mA in the remaining 58 percent with the majority of this subgroup requiring 0.6 to 1.0mA. 46 One possible reason for these inaccuracies was offered by Ben-David et al.: Varying tissue resistances could result in asymmetric current delivery, which could channel the current away from the nerve. 47 In summary, while NS indeed may not detect needle to nerve contact with 100 percent sensitivity, this may not translate into a significant clinical problem. NS techniques have enjoyed consistent success in the 90th percentile while also associated with low complication rates. However, the above discussed reports and the phenomenon described by Ben-David may contribute to our understanding of why PNB with NS by itself fails to achieve a 100 percent success rate. Limitations of Ultrasound Despite the initial excitement surrounding this technique, US visualization is still indirect and images are subject to individual interpretation. This results in a dependency of this modality on the skill of the sonographer. 48 Radiologists are required to undergo extensive training in US during their residency before their skills are considered adequate, an indication for the long learning curve that this specialty associates with US. 49 Additionally, in comparison to NS, which produces a threedimensional electrical field, US provides only two-dimensional information, which requires the operator to produce a three-dimensional map of the area in their mind. 50 Consequently, concerns have been voiced that the successful and safe practice of US for PNBs may actually require more training, a more detailed knowledge of anatomy, and even greater manual dexterity than NS. 50 Furthermore, the US beam itself is 1mm thin, introducing a technical challenge regarding continuous imaging of the needle. Consequently, Sites et al. identified 398 errors committed by US novices during performance of 520 PNBs. 48 The most common errors included failure to visualize the needle tip and failure to recognize maldistribution of local anesthetic. The difficulty to identify the needle tip is even further increased when out-of-plane approaches are utilized. In this setting, the only indication of the needle in the US image will be a single dot, leaving some uncertainty as to whether this dot is indeed the needle tip or a cross-section of the needle at any other level. 51 In addition, anatomic variations may limit local anesthetic spread despite ultrasound visualization. 52 Other technical issues such as acoustic shadowing caused by bony structures or tissue abnormalities such as edema or subcutaneous air, 53 may significantly impair the quality of nerve and needle visualization. It is therefore

19 10 Modalities of Nerve Block Performance Is there a Silver Bullet? not surprising that Barrington et al. required NS in 38 percent of cases to confirm the sonographic appearance when they performed sciatic nerve blocks at the midthigh level under US guidance. 54 As Tsui stated in an editorial accompanying Chan s previously mentioned study, we can never be totally sure of a nerve s identity, as even Chan s group using high-end ultrasound technology, failed to achieve 100 percent block success in the ultrasound guided groups. They commented that his is likely the result of mistaken nerve identity in Group US and misinterpretation of local anesthetic circumferential spread 16 Hopefully, further advances in US and needle technology will help us overcome some of these technical limitations. Synergy between Nerve Stimulation and Ultrasound I believe that NS and US exhibit synergistic effects during most steps of PNB performance (Table 3). Consequently, best practice may warrant combining the two modalities to truly improve important outcome parameters. It has been well described that one of the more challenging aspects of US is to maintain the needle position in the same plane with the US beam when performing in-plane approaches. 49 The fact that NS applies a three-dimensional search modality can alarm the operator of a needle approaching a nerve in cases where the needle tip has left the two-dimensional plane provided by the US image. The same is applicable when performing out-of-plane techniques, a situation in which the operator is almost always uncertain as to whether the needle cross-section observed in the US image represents the needle tip. While US may have advantages for nerve localization purposes and in terms of needle guidance to the target, NS can be helpful in those cases where US visibility is poor due to technical or tissue related limitations and artifacts. NS by itself has no means to warn the operator of adjacent structures such as the pleura when performing a supraclavicular block. The addition of US in this setting certainly will increase safety with the limitation that the needle in its entirety and the US beam need to be in the same plane at all times to avoid accidental pleural punctures out of view to the operator. The majority of nerves might be identifiable solely with US, especially once the structure in question is continuously scanned while following its course along an extremity in a distal direction. However, NS offers the option to quickly and definitively identify a nerve by providing a specific motor response. Finally, while US allows for observation of local anesthetic spread around the target structure, this modality can still result in inadequate intravascular local anesthetic application. NS can alarm the operator of inadequate local anesthetic delivery after as little as 1ml of the solution is injected and the motor response persists (failed Raj test). 55

20 Modalities of Nerve Block Performance Is there a Silver Bullet? 11 Steps of Nerve Block Performance Multi-Dimensional Ultrasound Nerve Stimulation Ultrasound Combined with Nerve Stimulation Method Nerve Localization Needle Guidance to Target Avoidance of Adjacent Structures Target Identity Confirmation Assurance of Adequate Local Anesthetic Delivery Table 3: Synergy between Ultrasound and Nerve Stimulation during Nerve Block Performance Conclusions Based on the currently available literature, it cannot conclusively be determined whether NS or US is superior to the other when it comes to success rate and the avoidance of complications. While one by itself may be the better modality for a certain technique or in a certain clinical scenario, the other may be equal or even superior for another. US-guided nerve blocks appear to have a faster onset time in some applications and can be performed with less local anesthetic requirements than a single shot NS-guided block. However, these differences may be of only academic nature for most clinical scenarios. On the other hand, combining US and NS offers versatility and reassurance, and the two modalities might be best used in a complementary fashion. While US can provide visual information regarding nerve and needle localization and spread of local anesthetic, NS allows the operator to gain information regarding nerve physiology and can reliably confirm a structures identity. In addition, if US visibility is inadequate, NS may still be utilized to confirm needle position prior to injection as well as to avoid inadequate local anesthetic delivery. Multimodal approaches are the standard of care in other areas of anesthesiology, for example in the treatments of acute pain and postoperative nausea and vomiting since they improve overall success and reduce side effects. I believe that such a multimodal approach could also offer benefits over a single modality when it comes to nerve block performance. Similar to the fact that the introduction of the airbag did not trigger calls to eliminate the seat belt, the anesthesia community should turn their attention to research regarding how the two techniques together can enhance success rates and patient safety, rather than debating if one modality should replace the other.

21

22 Dual Guidance : Integrating Nerve Stimulation and Ultrasound 13 Chapter 2 Dual Guidance: Integrating Nerve Stimulation and Ultrasound Admir Hadzic M.D., Ph.D. William Urmey M.D.

23

24 Dual Guidance : Integrating Nerve Stimulation and Ultrasound 15 Background Eliciting paresthesia or motor response to NS is commonly used when localizing nerves during PNB. Paresthesia is a mechanical-electrical phenomenon where mechanical stimulation of the nerve results in a sensory feeling described as an electric shock in the sensory distribution of the nerve that is being touched. In turn, electrical nerve localization relies on the use of electric current to elicit objective functional motor response of the nerve, which then indicates the intimate needlenerve relationship. Recently, more advanced functional and sophisticated modes of NS have been introduced in an attempt to make electro-localization of the targeted nerve or nerves more reliable. The introduction of high-resolution ultrasound (US) guidance during nerve blockade has significantly contributed to the enhanced accuracy and safety of PNB. Likewise, US guidance has also changed the technique of electrostimulation during nerve localization where NS may become an important adjunct to US guidance rather than the primary method of nerve localization. Objectives Currently, no standards or firm guidelines exist as to the role of NS in the era of USguided regional anesthesia. The purpose of this chapter is to present recent developments and to offer an introspective on how different methods of nerve localization vary and how they may be best combined the concept of dual guidance in clinical practice to increase the precision and safety when nerve blocks are performed. What is Dual Guidance? Dual guidance refers to the use of the two modalities, peripheral NS and US guidance, in combination to act synergistically. The aim of dual guidance is to achieve optimal nerve location and injection pattern while avoiding perineural structures and untargeted nerves, maximizing success and minimizing complications. Rather than being biased toward one given modality, best overall results can be obtained by utilizing the advantages offered by each, used together when possible. Although it is too early to form definitive conclusions, publications to date coupled with clinical experience supports this concept of dual guidance. For example, a study by Bloc et al. 57 published in 2007 documented a 100 percent success rate and better injectate spread visualized by US combined with a radial nerve motor response to NS, compared to a 86 percent success rate associated with a median nerve motor response. Dual guidance has been shown to reduce the time necessary for resident PNB in a study by Orebaugh et al. 56

25 16 Dual Guidance: Integrating Nerve Stimulation and Ultrasound Redefining Our Understanding of the Nerve Urmey and Stanton first studied the relationship between a sensory response (paresthesia) and a motor response to electrical stimulation during peripheral nerve or plexus block. 42 They demonstrated an ability to elicit a paresthesia in every patient studied during interscalene block, which constituted evidence that nerve contact was made by the tip of the needle in every case. Despite this evidence of nerve contact as well as successful surgical anesthesia and sensory evidence that showed that the tip of the needle was located in the interscalene space, there was an inability to elicit motor nerve stimulation in 70 percent of the patients with stimulation up to 1.0 ma, 0.2 ms pulse duration. This was the first demonstration that sensory fascicle contact could be made while the tip of the needle was sufficiently remote or shielded from motor fascicles or motor components. Subsequent to the initial presentation of the above data, similar findings were reported by Choyce et al. 43 in a study of 72 patients who received axillary brachial plexus block. In their study, paresthesia was associated with a motor response to electrical stimulation up to 0.5 ma in only 77 percent of study patients. In an editorial reply shortly after these publications, Urmey and Stanton argued, there is every indication and reason to believe that nerve contact occurs during peripheral nerve or plexus blockade. They suggested, we might begin to ask ourselves how we can prove that no nerve contact occurs when we elicit sensory or motor responses during peripheral nerve blocks. Furthermore, they proposed that two-dimensional ultrasonographic examination of nerves during paresthesia can eventually help to answer this question. 58 Since that editorial was published, multiple reports of the occurrence of nerve contact or intraneural placement of the stimulating needle tip have indeed been demonstrated during US observation without the ability to stimulate in the low amperage range. Reinforcing the conclusions of the above authors, Chan et al. 59 published a study in 2007 that evaluated minimum stimulating current associated with deliberate intraneural needle placement in pigs. They found the minimum current required to elicit a motor response ranged from ma, 0.1 ms. Of note, in a study performed by Bollini et al. 60 on 22 patients who received interscalene block by NS guidance after motor response at 0.5 ma 0.1 ms was obtained, the stimulator was turned off and the needle further advanced to paresthesia. Paresthesia was elicited with further needle advance in 95 percent of the patients. Recently, Bigeleisen 61 studied axillary block utilizing US guidance after the elicitation of a paresthesia or deliberate piercing of the fascia around the nerve by the sensation of a pop. He found that the paresthesia was frequently associated with subsequent intraneural injection documented by US imaging. Despite puncturing of the peripheral nerves and apparent intraneural injection, there were no neurological injuries.

26 Dual Guidance : Integrating Nerve Stimulation and Ultrasound 17 Although nerve contact or intraneural placement of the needle tip frequently occurs, it is not always associated with the ability to stimulate motor fascicles in the very low current range (0.1 ma). This argues for a lack of sensitivity of NS, but only in this very low current range. One must be careful not to confuse this lack of sensitivity in the low current range with a lack of specificity or accuracy. Electrical NS is extremely specific in the low current range (0-0.5 ma, 0.1 ms pulse duration). Electrical NS has a very high sensitivity with higher current levels and pulse durations. It is only insistence upon a very low stimulating current to ensure this high specificity when NS is the only surrogate method of determining needle-to-nerve proximity, resulting in the demonstrated lack of sensitivity in the studies by Urmey and Stanton, and Choyce et al. The combination of NS with another surrogate method of determining needle-tonerve proximity such as US allows for greater sensitivity of each technique and allows one to drop the insistence upon motor response in the very low current range if needle position and local anesthetic spread can be directly observed. Nerve Stimulation, Ultrasound or Both: Which Modality Should I Use? By stark contrast to the historical paresthesia technique, the more modern scientific modalities of electrical NS and US guidance provide useful information for the distance during needle exploration from the nerve prior to nerve contact. Each of these modalities has inherent associated benefits as well as limitations. It is important for the clinical practitioner to be open to the use of either technique or the combination of the two. Rather than polarizing practitioners toward one modality for nerve location, the object of this chapter is to educate the clinician with regard to each modality and how they can be combined effectively to facilitate nerve location, ultimately benefiting the patient receiving peripheral nerve or plexus blocks. 10 Reasons for Combining the Use of NS with US: Why Use a Dual Guidance Approach? 1. In contrast to US, which utilizes a qualitative anatomical endpoint, NS yields a quantitative, scientifically based endpoint that has been associated with extremely high success rates. US guidance has not been shown to increase success rates over those associated with use of NS. As discussed in the review by Neal et al. 62 single stimulation infraclavicular block can achieve success rates of 97 to 100 percent. It is difficult to exceed such published success rates. Soares et al. 63 pointed out that when using US guidance without optimal needle position that block success rate can be unpredictable. NS yields graded functional information at distance from or close proximity to not only the targeted nerve, but also other nerves encountered during needle exploration.

27 18 Dual Guidance: Integrating Nerve Stimulation and Ultrasound 2. US guidance is a two-dimensional modality. In order to be certain of needle tip location relative to the nerve, orthogonal views would be necessary. In practice these are difficult if not impossible to obtain. NS has the advantage of being a three-dimensional modality and therefore does not limit the needle trajectory used during exploration. By contrast to US, needle direction can be determined solely based upon anatomical concerns to facilitate location and minimize complication. 3. Use of catheter techniques can be problematic with US guidance. It is often necessary to have a third hand available to hold the probe in order to allow the operator to pass the catheter through the needle. In addition, the catheter often moves out of the plane and becomes invisible after it is passed beyond the needle tip. Stimulating catheters can be used to assure proper positioning of the catheter tip within a plexus. 4. US guidance has an inability to image a needle tip when using the out-of-plane approach, which is often necessary for deeper nerves. NS works for all peripheral block procedures and is not limited by the depth of the nerves or plexus from the skin, making deeper blocks such as lumbar plexus blocks relatively easy to perform. 5. US guidance has numerous artifacts and pitfall errors that have been associated with the technique. 64,65 These include missing structures or falsely perceived objects, absent blood flow when blood flow actually exists, degraded images, tissue reverberation artifact, and bayonet artifact. NS can be used to verify the identity of a nerve through a qualitative anatomical endpoint, or an alternative structure through absence of motor response. 6. The portability of nerve stimulators and their affordability make NS easily accessible. 7. The need for transport, set-up and use of sterile coupling gels, probe covers, etc., all need to be factored into block performance time with US guidance. Nerve stimulators are readily available and quick to set up. 8. The major advantage of US is that it allows real-time imaging of the anatomy and can be used to identify abnormal anatomy. Real-time imaging allows for information of needle-to-nerve position during exploration. 9. US guidance provides the ability to observe local anesthetic spread pattern during injection. By contrast, NS is a blind modality and once injection has been made, further information may be limited as a result of the injection. 10. Like NS, US guidance is a scientific method for ascertaining the position of the needle relative to the nerve. US serves as an excellent teaching tool because imaging can be observed by students or anesthetists in training.

28 Dual Guidance : Integrating Nerve Stimulation and Ultrasound 19 Dual Guidance in Practice: How Does It Work? The advantages of US-guided blocks are that the needle, peripheral nerve and the spread of the local anesthetic can be visualized during the procedure. Logically, as the results of the current research efforts seem to indicate, 66 this should make US-guided PNBs more reproducible and possibly more time-efficient. It should be noted however, that peripheral NS has been extensively studied and therefore universally accepted as a standard PNB technique for more than 30 years. 67 Consequently, NS is still being used as a reference technique in many studies of US-guided blocks, although this may change depending on how the US technology, its ease of use and necessary training required for its successful application evolve. The following paragraph will discuss advantages and disadvantages of using NS in conjunction with US guidance during PNBs. The most radical proponents of US-only PNBs maintain that nerve stimulation adds unnecessary cost to the procedure due to the cost of insulated needles ($7-12) and nerve stimulators ($500-1,000). However, these expenses should be contrasted against the costs of acquisition of an ultrasound machine ($30,000-65,000) and a yearly maintenance contract ($2,000-5,000). In addition, with regular use, an ultrasound machine will likely need a replacement within five to seven years due to the wear and tear in the equipment-unfriendly environment of operation rooms or due to becoming obsolete as newer, better units are being released. Additional costs of US-guided PNBs include the need for PC support, data storage and archiving, image printing, and US accessories such as additional probes ($8,000 15,000), sterile acoustic medium, sterile probe sleeves, among others. It is unlikely that any potential saving in time with US blocks will offset the discrepancy in these costs. 33 When the nerve and needle path are adequately visualized during US-guided PNBs, NS may perhaps be unnecessary as a routine. However, adequate visualization of tissue-needle interface may not be readily achievable in all patients and/or by all users. 51 It should be kept in mind that US provides anatomical information whereas NS provides functional information. Therefore, these two nerve localization modalities are not mutually exclusive but complementary, particularly when the US imaging is suboptimal and/or significant expertise is not available (presently common scenario). What has changed is the technique of NS when used in conjunction with US. More specifically, the fine-tuning of the needle position using progressively lower current intensity becomes unnecessary. This is because the motor response is used primarily for additional confirmation of the needle placement as well as a security step should the needle be advanced through the nerve or a plexus without being visualized on ultrasound as seen in Figure 2.

29 20 Dual Guidance: Integrating Nerve Stimulation and Ultrasound Figure 2: Flow chart for Dual Guidance nerve block Several studies found that US-guided PNBs may have a higher success rate than NSassisted PNBs. 68 At least one study also suggested that NS may not increase the success rate when used in conjunction to US PNBs. 69 Successful nerve localization, however, depends on the operators experience regardless of whether US or NS technique is used. The success rates reported with studies comparing NS- vs. US-guided blocks are often unrealistically low. For instance, US blocks resulted in 82.8 percent of successful PNBs vs percent in NS in axillary brachial plexus blocks. 21 If the failure rates with these blocks were indeed so high, PNBs would have no use in modern anesthesiology. Much too often, the data on success rates represent dermatomal distribution of the blocks,

30 Dual Guidance : Integrating Nerve Stimulation and Ultrasound 21 which may not translate into clinical effectiveness. A study by Casati, for instance, suggests that US is not superior to NS PNBs. 13 Therefore, in the hands of experienced anesthesiologists, there may not be a clinically significant difference in success rate between US and NS nerve blocks. Use of US guidance for PNBs is in its infancy and one can only hope that it achieves the same high success rate and low complication rate associated with the use of NS. Thus far, use of US guidance has shown great promise for certain peripheral or plexus nerve blocks. Due to the relatively low incidence of PNB-related nerve injury and lack of virtually any monitoring during PNB, the risk factors of neurological complications remain inadequately studied. In the absence of objective information in PNB documentation, recall bias is almost inevitable in retrospective studies or case reports of nerve injuries. Commonly cited risk factors include elicitation of paresthesias, 70, 5 pain on injection, 71 high injection pressure, 72 injection current <0.2 ma. 73 However, none of these factors have been clinically proven to be predictive of nerve injury. US may be helpful in detecting, but not preventing, an intraneural injection as the location of the injectate is seen only after the injection is initiated. Since only a miniscule amount of local anesthetic is necessary to rupture the perineurium, US is not a reliable tool to prevent fascicular injury. 72 On the other hand, avoiding injection when evoked motor response to NS is present with <0.2 ma (0.1 msec) may theoretically be helpful in reducing the risk of an intrafascicular injection, making another case for use of NS in conjunction with US. 73 Another clear advantage of dual guidance is the added functional information. Permanent phrenic nerve injury has been reported following interscalene brachial plexus block. 74 The phrenic nerve is a small nerve that is very difficult and often impossible to visualize when US-guided block is performed above the clavicle. By contrast, phrenic contractions are easy to elicit when NS is added to aid in nerve location. Such functional feedback in the form of diaphragmatic contractions serves as a warning and allows the practitioner to avoid inadvertent injection into the phrenic nerve or nerve root fibers that contribute to the formation of the phrenic nerve. Similarly, during the common periarterial out-of-plane approach to blocking the brachial plexus at the level of the cords during infraclavicular block, the lateral cord is often not visualized and lies directly in the path of the needle s trajectory, leaving it vulnerable to being transected or impaled without the knowledge of the practitioner. Use of dual guidance results in the ability to identify the lateral cord. An example of dual guidance that offers advantages over either NS or US guidance used alone is when out-of-plane visualization of the brachial plexus is coupled to conventional NS with needle trajectory in the direction described in the original description of the interscalene block of Winnie. 75 The plexus can be visualized in cross-