Introduction

Published on 27/02/2015 by admin

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CHAPTER 1 Introduction

Within anesthetic practice, the role of regional anesthesia – including peripheral nerve block – has expanded greatly over the past two decades. In 1998, a national survey demonstrated that 87.8% of US anesthesiologists make use of regional techniques.¹ This widespread use arises in part from the widely held belief (to some extent evidence-based) that, at least in some settings, anesthetic techniques that avoid general anesthesia offer real advantages in terms of patient outcome.² For instance, Chelly and colleagues have demonstrated clearly that continuous femoral infusion of ropivacaine 0.2% in patients undergoing total knee replacement provides better postoperative analgesia than epidural or patient-controlled analgesia. Critically, this technique accelerated early functional recovery and was associated with decreased duration of hospital stay, postoperative blood loss, and incidence of serious postoperative complications.³

A second reason that accounts for the recent increase in peripheral nerve block practiced in developed countries is the greater proportion of surgical procedures carried out as ‘day cases’. Regional anesthesia plays a fundamental role in the future of day case or ambulatory anesthesia, both as an intrinsic component of the anesthetic technique and for effective postoperative analgesia.⁴ Currently, 60–70% of all surgical procedures performed in the USA are day cases. It is likely that peripheral nerve block, used appropriately in the ambulatory setting, decreases the time to discharge from hospital, improves patient satisfaction and postoperative analgesia, facilitates rehabilitation, and results in fewer complications than conventional analgesic techniques.

Third, the practice of peripheral nerve block has increased because of advances in technique, equipment, and our understanding of how and when it is indicated. These advances include the use of superior peripheral nerve stimulators and ultrasound for nerve localization and the use of indwelling catheters for ‘continuous’ techniques.

The content

This publication comprises a textbook, atlas, and practical guide to peripheral nerve block, which presents material as text and images, including video clips, magnetic resonance (MR) images, ultrasound images, still photographs, and line drawings. It is probably best regarded and used as an educational tool.

The textbook is in two parts. Part I covers the history, pharmacologic principles, and clinical applications of peripheral nerve blockade as well as the materials and equipment currently in use. It also covers training in peripheral nerve blockade. In Part II, each chapter addresses a single block and describes its specific indications, relevant anatomy (including surface anatomy), and how the procedure is performed. The anatomy is presented using photographs of cadaveric dissections and volunteers (for surface anatomy), MR images, ultrasound images, and sometimes line drawings. On the accompanying DVD-ROM, the anatomy and block technique are demonstrated using video clips; ‘live’ anatomy and spread of injectate are demonstrated using MR images. Chapters in Part II contain ‘clinical pearls’ intended to impart specific advice for improving success rates or avoiding problems. Associated with each chapter is a self-assessment section aimed at providing a means of evaluating both retention and comprehension of the information presented. This can be found at the associated website.

We have carefully selected the blocks for inclusion as those that are currently an established part of clinical anesthetic practice. We have attempted to describe those that will be of greatest interest and use to clinicians learning or practicing peripheral nerve blockade today. For instance, although parasacral, subgluteal, popliteal, and other approaches have been described for block of the sciatic nerve, we have opted to describe only the more widely practiced classic anterior and posterior approaches. We have also excluded central neuraxial blocks (spinal and epidural techniques) and pediatric peripheral nerve blocks.

The readership most likely to benefit

It is widely recognized that anesthetists are incompletely trained unless they are proficient in the performance of peripheral nerve block.⁵ Anesthetists comprise the single largest group of hospital doctors. Approximately 5% of all physicians in the USA practice anesthesia. In some countries, anesthesia is also practiced by nurse anesthetists.

The material contained in both the textbook and the DVD-ROM will be of greatest use to those practicing or learning anesthesia as a specialty. This group includes anesthetists (anesthesiologists), anesthetic trainees, and nurse anesthetists. Used in slightly different ways, this publication will provide a useful introduction to the practice of peripheral nerve blockade, a means of preparing for examinations (boards and fellowships), and a means of extending the range of practitioners’ techniques or refreshing them with regard to a particular technique that they have not performed for some time. We have made no assumptions as to the background or experience of our readers. Therefore the techniques and practice are explained from first principles: anatomic, pharmacologic, and safety. Occasional practitioners of peripheral nerve blockade – whether anesthetists, emergency medicine physicians, or surgeons – are strongly advised to review Part I before moving to Part II to learn how to perform a particular block.

How to use the content most effectively

First, it is important that readers who have little or no experience with peripheral nerve blocks – such as anesthetic trainees commencing the ‘regional’ or peripheral nerve block module of their training program – learn the principles underlying peripheral nerve blockade, outlined in Part 1 of the textbook, before studying specific blocks. This is intended to avoid the risk of training or being trained as a technician. It is essential that peripheral nerve blocks be performed only by a practitioner with a sound understanding of how neural blockade is pharmacologically induced. This is to ensure that informed decisions are made regarding the suitability of a patient for peripheral nerve blockade or how best to treat a complication.

Second, an understanding of the anatomy (surface landmarks, nerves, plexuses, and their relations) relevant to a block is essential to ensure that a successful block is consistently and safely achieved. The anatomic material presented comprises text, line drawings, still photographs, video clips, and MR images. Our suggestion is that the relevant anatomy sections be read from the textbook with immediate reference to the accompanying still images in order to reinforce conceptualization of the structures. This represents the first step to forming a mental image or model of the region. The second step entails playing the video clips of cadaveric dissection from the DVD-ROM and revising the still images, which are also displayed on the DVD-ROM for convenience. The next step in learning the relevant anatomy is to play the surface anatomy video clip, because this represents the bridge between the mental anatomic model that has been formed and the block technique, displayed immediately after the surface anatomy on each video clip.

Third, readers who wish to refresh their memory on a particular block, or commence learning about a new block, should first read the appropriate chapter in the textbook and then use the corresponding chapter in the DVD-ROM to reinforce (using video clips and MR images) the information they have read.

Fourth, it is advisable that the self-assessment sections be undertaken only after all the material on a particular block has been covered. The questions are designed to test both retention of information about and understanding of the relevant anatomy, technique, and clinical application of the block.

Finally, as readers may not be familiar with viewing MR images, a brief outline of the equipment used, principles, and image characteristics is presented below. This is worth reading before attempting to collate the MR images with either the cadaveric or surface anatomy images presented.

Magnetic resonance imaging

Equipment

We use MR images in this textbook and DVD-ROM because of the excellent soft tissue contrast they provide, without exposing our volunteers to the ionizing radiation associated with computerized tomography and X-ray. Using the combination of a strong magnetic field and radiofrequency pulses, magnetic resonance imaging (MRI) obtains a digitized image of an anatomic area.

We used the Toshiba 0.35T OPART, open system.⁶ This scanner uses superconducting technology and high-speed gradients to produce high-quality images. The scanner was selected on the basis of its well-documented advantages; namely, that its open architecture allows comfortable volunteer positioning, easy access for injection, and prevents problems associated with claustrophobia.⁷^–⁹ A number of transmit and receive coils were used, appropriate to the anatomic area being scanned.