Advances in Anesthesia 2013 (eBook)

Advances in Anesthesia 2013

Thomas M. McLoughlin (Autor)

eBook Download: EPUB

2014 | 1. Auflage
100 Seiten
Elsevier Health Sciences (Verlag)
978-1-4557-7294-0 (ISBN)

Infos

Each year, Advances in Anesthesia brings you up-to-date with the latest knowledge from the preeminent practitioners in your field. A distinguished editorial board identifies current areas of major progress and controversy and invites specialists from around the world to contribute original articles on these topics.

Textauszug

Elicitation of Paresthesia, Peripheral Nerve Stimulation and Intraneural Injection

New Insight Provided by Ultrasonography

De Q.H. Tran, MD, FRCPC∗ [e-mail], Wallaya Techasuk, MD and Roderick J. Finlayson, MD, FRCPC,     Department of Anesthesia, Montreal General Hospital, McGill University, 1650 Avenue Cedar, D10-144, Montreal, Quebec H3G 1A4, Canada

∗Corresponding author.

Keywords

Ultrasonography

Paresthesia

Peripheral nerve stimulation

Intraneural injection

Key points

• By enabling operators to visualize the nerve, needle, and local anesthetic (LA) spread, ultrasound guidance has contributed to improve the efficacy of peripheral nerve blocks. Moreover, these ultrasound-derived advantages have also provided much insight into the limitations of elicitation of paresthesia (EP) and peripheral nerve stimulation (PNS) as well as the safety of intraneural injection.

• The ability to visualize LA spread in real time can explain why the success rates of EP- or PNS-guided blocks were never 100%.

• Ultrasonography has revealed that block success depends mainly on circumferential spread of LA around the nerve.

• The ability to follow needle advancement in real time has revealed that 3 distinct events can occur during the performance of a nerve block: needle-nerve contact, EP, and elicitation of an evoked motor response.

• The ability to visualize the nerve has revealed that, while specific, 0.2 mA-minimal stimulatory currents lack sensitivity in preventing intraneural injection.

Introduction

By enabling operators to visualize the nerve, needle, and spread of local anesthetic agents, ultrasound guidance has revolutionized the practice of regional anesthesia. In recent years, several review articles have outlined the benefits of ultrasonography (US) in comparison with traditional modalities such as elicitation of paresthesia (EP) and peripheral nerve stimulation (PNS) [1–9]. However, the advantages conferred by US far exceed the improved success rate of peripheral nerve blocks. For instance, the ability to visualize the needle tip in relation to the physical confines of a neural structure provides insight into the needle-nerve distance required for successful blocks, and offers new answers (as well as questions) to old quandaries afflicting PNS and EP. To date, this topic has been overlooked by most practitioners. Thus, this narrative review sets out to peruse human trials (published in the English language) pertaining to ultrasound-guided nerve blocks. The goal is to query the available literature for new or confirmatory information pertaining to (1) limitations of EP, (2) limitations of PNS, and (3) intraneural injection.

Elicitation of paresthesia

State of knowledge before the advent of ultrasonography

Before the advent of PNS and US, regional anesthesiologists relied mainly on EP to ensure that the needle tip was positioned next to the nerve before the injection of local anesthetic (LA) agents. In 1953, Daniel Moore [10] coined the famous dictum: “no paresthesia, no anesthesia.” Though succinct, the latter enforced a very clear message: successful nerve blockade demands utmost proximity, if not direct contact, between a needle tip and a nerve, as evidenced by the occurrence of mechanical paresthesias. Subsequently, many investigators have questioned the validity and safety of such a recommendation [11,12]. For instance, in a series of 21,278 peripheral nerve blocks, Auroy and colleagues [13] observed that all cases of postoperative neurologic dysfunction (N = 4) were associated with paresthesia during needle puncture or with pain during LA injection. However, paresthesias can occur with other modalities (PNS technique, transarterial injection) as well, and thus should not be equated solely with EP-guided techniques. In fact, Selander and colleagues [14] reported similar rates of nerve injury in axillary blocks performed with EP or transarterial injection (0.8%–2.8%). In 2006, Liguori and colleagues [15] randomized 217 patients to PNS-guided or EP-guided interscalene block. These investigators found no differences in the incidences of postoperative neurologic symptoms at 1 week (9.3%–10.1% of patients). Symptoms resolved in all patients within 12 months. Of note, 23% of subjects in the PNS group experienced paresthesia during needle insertion. In 2 large studies (combined total of 4003 patients), Horlocker and colleagues [16] and Fanelli and colleagues [17] concluded that tourniquet time and inflation pressure, but not mechanical paresthesia, predisposed to postoperative nerve injury. Nonetheless, despite the lack of definitive evidence linking EP and neural deficit, the collective bias against the former prompted an amendment to Moore’s dictum: “no paresthesia, no dysesthesia” [12].

New insight provided by ultrasonography

Since 1953, we have learned that paresthesias are not required to ensure a successful nerve block. For instance, transarterial injection and loss of resistance can be used to anesthetize the axillary brachial plexus and femoral nerve (fascia iliaca compartment block), respectively [1,18]. Neurostimulation and US constitute additional modalities that do not depend on paresthesias to locate and block a nerve. Conversely, the occurrence of paresthesia, in itself, does not guarantee success. For instance, Boezaart and colleagues [19] observed a 10% failure rate with EP-guided interscalene blocks. For axillary blocks, the success rate with EP ranges from 40% to 90% [20,21], with most trials reporting rates between 76% and 82% [22–25]. These findings, which were previously puzzling, can now be explained with US. Neural blockade is mediated by LA; positioning the needle tip close to the nerve can result in failure if circumferential LA spread does not occur around the nerve [26]. In summary, paresthesias no longer ensure anesthesia, nor does anesthesia require paresthesias anymore.

The controversy related to the safety of EP-guided nerve blocks cannot be solved with US at this time. Though first reported in 1978 [27], US has only penetrated routine clinical practice in the last 10 years. Furthermore, US is seldom combined with intentional EP for peripheral nerve blocks. These 2 factors explain the limited contribution of ultrasound guidance to the understanding of EP's safety. However, US has been instrumental in shedding new light on an unexplained phenomenon: the neurophysiologic mechanism of paresthesia. In the past, the latter was conceptualized (simply) as the inevitable consequence of needle-nerve contact. Conversely, a lack of paresthesia during LA injection was routinely used to denote safety, a guarantor that the needle tip was at a safe distance from the nerve. Because US allows the operator to visualize neural structures, regional anesthesiologists have become increasingly aggressive with their choice of targets. For supraclavicular blocks, the needle tip can now be placed inside the neural cluster formed by the confluence of trunks and divisions of the brachial plexus [28,29]. For axillary blocks, Bigeleisen [30] has reported his initial experience with LA injection inside the terminal nerves. Despite these intracluster/intraneural positions of the needle tips, paresthesias did not occur in all subjects. For instance, with ultrasound-guided supraclavicular blocks, Tran and colleagues [28] and Roy and colleagues [29] reported 19.6% and 45.1% incidences of paresthesia, respectively. On the other hand, Bigeleisen [30] recorded a paresthesia with almost all cases of radial and median nerve puncture. By contrast, only 50% and 79% of patients reported paresthesias with penetration of the musculocutaneous and ulnar nerves, respectively. These findings echo a fact well known to most practitioners and US enthusiasts: paresthesias can be conspicuously absent despite sonographic evidence of needle-nerve contact. Russon and Blanco [31] even reported a case whereby LA injection inside the musculocutaneous nerve failed to generate a paresthesia. These recent US-driven observations beg the question: why do paresthesias occur?

The genesis of a paresthesia remains a deceptively complex neurophysiologic phenomenon. An axon generates signals only at its terminal end [32]; thus, mechanical encroachment on its central portion (during peripheral nerve blocks, for example) should theoretically be imperceptible to the patient. Yet paresthesias do arise with needle-nerve contact. Karaca and colleagues [33] hypothesized that paresthesias do not result from contact with the nerve but from mechanical stimulation of the nerves to the nerve (ie, nervi nervorum). This elegant premise would certainly explain why paresthesias arise often, but inconsistently, despite sonographic confirmation of neural contact by the needle tip. In other words, if the latter were to contact the axon in an area devoid of nervi nervorum, the event would not translate into a shock-like...

Produkt-Details

• Erscheint lt. Verlag: 12.11.2014
• Sprache: englisch
• Themenwelt: Medizin / Pharmazie ► Gesundheitsfachberufe
• Themenwelt: Medizin / Pharmazie ► Medizinische Fachgebiete ► Anästhesie
• ISBN-10: 1-4557-7294-1 / 1455772941
• ISBN-13: 978-1-4557-7294-0 / 9781455772940