Principles and Practice of USin Regional Anesthesia

Darto Satoto

Introduction

The recent use of ultrasound imaging inperipheral regional anesthesia allows theoperator to see neural structures, guide theneedle under real-time visualization, navigateaway from sensitive anatomy, and monitor thespread of local anesthetic.

Nerve identification with ultrasound

Peripheral nerves have a fascicular echotexture.This means that when viewed on a transversescan (short-axis view) peripheral nerves have a"honey-comb" appearance.

Transverse scanning by sliding a broad lineartransducer is the preferred method for followinga nerve along its course.

Martinoli C, Bianchi S, Derchi LE: Ultrasonography of peripheral nerves. Semin Ultrasound CT MR 2000;21:205-213.

Anisotropy

Peripheral nerves exhibit anisotropy. Thisimplies the amplitude of the received echoeswill vary with the angle of insonation. Anglechanges as small as 10 degrees away fromperpendicular to the axis of the nerve willsubstantially reduce its echogenicity.

Grechenig W, Clement HG, Peicha G, et al: [Ultrasound anatomy of the sciatic nerve of the thigh] Biomed Tech (Berl) 2000;45:298-303.

Doppler

Recently a new color Doppler technology hasbeen developed. The advantage of powerDoppler is that it is more sensitive at detectingblood flow than velocity imaging (by a factor of3 to 5 in some cases).

APPROACHES TO REGIONAL BLOCK WITHULTRASOUND

Two basic approaches to needle placement withultrasound guidance are in common use. Withthe out-of-plane approach the needle crossesthe plane of imaging as an echogenic dot.

With the in-plane approach the full needle tipand shaft are visualized along the axis of theneedle.

Target nerve

The target nerve can be viewed in short axis(SAX) or in long axis (LAX). SAX views of thetarget have dominated regional blocks becausethe views are stable and provide assessment ofcircumferential distribution of the injected localanesthetic. LAX views of large, straight vesselsare sometimes used for vascular accessprocedures.

IMAGING OF THE BRACHIAL PLEXUS

High-frequency linear probes, in the range of 10to 15 MHz, are best suited for imaging thebrachial plexus in most locations, exceptperhaps the infraclavicular region, where thecords may be more deeply located and thusprobes in the 4- to 7-MHz range may berequired.

The Interscalene Region

In the interscalene region, the cervical rootsforming the plexus are located between theanterior and middle scalene muscles. They arebest visualized when scanned in the lateralaspect of the neck in an axial oblique plane.

The Supraclavicular Region

In the supravlavicular region, the brachial plexusis best scanned with a linear probe in a coronaloblique plane. The subclavian artery is the mostprominent landmark identified immediatelysuperior to the first rib. The trunks, or divisions,of the plexus in this region are tightly arrangedwithin what seems to be a single sheath,immediately lateral and cephalad to thesubclavian artery.

Infraclavicular Region

In the infraclavicular region next to the coracoidprocess, the cords of the plexus lie deep to thepectoralis major and pectoralis minor muscles.They can be best imaged with a linear probe inthe range of 4 to 7 MHz, in a parasagittal plane,immediately medial to the coracoid process.

Axillary Region

At this level, terminal branches of the brachialplexus, such as the musculocutaneous, median,ulnar, and radial nerves, are located superficially,usually within 1 to 2 cm of the skin. A linear 10-to 15-MHz probe is therefore recommended.

LUMBOSACRAL PLEXUS

The lumbar plexus (L1 to L5) and the sacralplexus (S1 to S4) provide innervation to thelower extremity. Unlike the brachial plexus, thelumbosacral plexus and its proximal branchesare quite deep. Sonographic imaging can bemore challenging except for the distal peripheralbranches.

Lumbar Plexus Block

Ultrasound imaging of the lumbar plexus in theparavertebral region in adults is technicallydifficult because of its deep location. Usingcurved 4- to 5-MHz transducers, Kirchmair andassociates identified the lumbar plexus withinthe psoas muscle and correlated ultrasoundimages with anatomic specimens.Kirchmair L, Entner T, Wissel J, et al: A study of the paravertebralanatomy for ultrasound-guided posterior lumber plexus block.Anesth Analg 2001;93:477-481.

Femoral Nerve

The three main terminal branches of the lumbarplexus are the femoral, obturator, and lateralfemoral cutaneous nerves. The femoral nervederived from L2 to L4 is the largest branch andcan be easily imaged in the inguinal region usinga linear 8-12 MHz transducer.

Sciatic Nerve

The sciatic nerve also originates from thelumbosacral plexus (L4 through S3) and entersthe gluteal region through the greater sciaticforamen, between two muscle planes. Theanterior muscle plane is formed by theobturator internus and inferior gemellusmuscles, and the posterior, more superficialmuscle plane by the gluteus maximus muscle.

Neuraxial Block

The application of ultrasound guidance inneuraxial blockade is gaining popularity,although it is not yet as widespread as inperipheral nerve blockade.

Ultrasound Imaging of Spine

1. Paramedian sagittal

2. Paramedian sagittal oblique

3. Transverse

ISSPS 2011 Hongkong, p.119

Paramedian sagittal transverse process view of the lumbar spine and corresponding MRI image (T1-weighted). (ISSPS 2011)

Paramedian sagittal articular process view of the lumbar spine and corresponding CT image (bone window setting). (ISSPS 2011)

Paramedian sagittal oblique view of the lumbar spine and corresponding MRI image (T1-weighted). (ISSPS 2011)

Spinous process view of the lumbar spine and corresponding MRI image (T1-weighted). (ISSPS 2011)

Transverse interlaminar view of the lumbar spine and corresponding MRI image (T1-weighted). (ISSPS 2011)

Surface marking to guide needle insertion. In the paramedian sagittal oblique view. Each interspace (L3-4 in this case) is centered in turn on the ultrasound screen (A). A corres-ponding skin mark is made at the midpoint of the probe’s long edge (B). The probe is then turned 90º to obtain the transverse interlaminar view (C). The midline is centered on the ultrasound screen and skin marks are made at the midpoint of the probe’s long and short edges (D). The intersection of these two marks provides an appropriated needle insertion point for midllineapproach to the epidural or intrathecal space at that level. (ISSPS 2011)

Ultrasound Imaging of the Sacrum (Caudal Block)

Textbook of RA and Acute PM, Admir Hadzic p.270McGraw Hill 2007

Ultrasound Imaging of the Sacrum (Caudal Block)

Sonographic transverse view of the sacrial hiatus. The two sacral cornua, the sacral hiatus, the sacrococcygeal ligament and base of sacrum were identified. (ISSPS 2011)

Ultrasound Imaging of the Sacrum (Caudal Block)

Sonographic longitudinal view of the sacral hiatus and caudal epidural space. The sacral hiatus, caudal epidural space, sacrococcygeal ligament, base of sacrum, the cleft of sacrococcygeal junction and base of coccyx were identified. (ISSPS 2011)

Ultrasound Imaging of the Sacrum (Caudal Block)

The advancement of the needle with the bevel facing posteriorly under sonographic longitudinal view of the sacral hiatus and caudal epidural space. The small arrows indicate the path of the needle. (ISSPS 2011)

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