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On-line version ISSN 1806-907X
Rev. Bras. Anestesiol. vol.57 no.6 Campinas Nov./Dec. 2007
Ultrasound images of the brachial plexus in the axillary region*
Imágenes ultra-sonográficas del plexo braquial en la región axilar
Diogo Brüggemann da ConceiçãoI; Pablo Escovedo Helayel, TSAI; Francisco Amaral Egydio de CarvalhoII; Jaderson WollmeisterII; Getúlio Rodrigues de Oliveira Filho, TSAI
do CET Integrado de Anestesiologia da SES-SC; Membro do Núcleo de Ensino
e Pesquisa em Anestesia Regional do HGCR
IIME2 do CET Integrado de Anestesiologia da SES-SC
OBJECTIVES: The axillary artery is the anatomical reference, in the surface,
for axillary brachial plexus block. Anatomic studies suggest variability in
the location of the structures in the brachial plexus in relation to the axillary
artery. These variations can hinder blocks by neurostimulation. The ultrasound
allows the identification of the structures within the brachial plexus1.
The objective of this report was to describe the position of the nerves in the
brachial plexus in relation to the axillary artery.
METHODS: Thirty volunteers of both genders were studied. They were in the supine position with 90° abduction and external rotation of the shoulder and 90º flexion of the elbow. Using a 5 cm and 5-10 MHz digital transducer, median, ulnar and radial nerves were identified and their position in relation to the artery were recorded in an 8-sector sectional graphic chart, numbered in crescent order starting at the 12-hour position (medial), whose center represented the axillary artery.
RESULTS: The median nerve was located mainly in sectors 8 (55%) and 1 (28%) (medial); the radial nerve was predominantly in sectors 4 (59%) and 5 (34%) (lateral); and the ulnar nerve in sectors 2 and 3 (inferior) in 69% and 24% of the cases, respectively. There was a considerable variation in the location of the nerves in relation to the superior and inferior aspects of the artery.
CONCLUSIONS: Real-time ultrasound inspection of the neurovascular structures of the brachial plexus in the axilla demonstrated that the median, ulnar and radial nerves have different relations with the axillary artery.
Key Words: ANATOMY: brachial plexus; ULTRASOUND: peripheral nervous system.
Y OBJETIVOS: La arteria axilar es una referencia anatómica de superficie
para el bloqueo del plexo braquial por vía axilar. Estudios anatómicos
sugieren variabilidad de las posiciones de las estructuras nerviosas del plexo
braquial con relación a la arteria. Esas variaciones pueden dificultar
bloqueos por neuro estimulación. El ultrasonido permite la identificación
de las estructuras del plexo braquial 1. Ese estudio buscó
describir el posicionamiento de los nervios del plexo braquial con relación
a la arteria axilar.
MÉTODO: Fueron estudiados 30 voluntarios de los dos sexos, en posición supina con abducción a 90° y rotación externa del hombro y flexión del codo a 90°. Utilizando transductor digital de 5 cm y 5-10 MHz, fueron identificados los nervios mediano, ulnar y radial, y las respectivas posiciones en relación a la arteria fueron marcadas en una carta gráfica seccional de 8 sectores, enumerados en orden creciente a partir de la hora 12 (medial), cuyo centro representaba la arteria axilar.
RESULTADOS: El nervio mediano se ubicó predominante en el sector 8 (55%) y en el sector 1 (28%) (mediales); el nervio radial se ubicó predominantemente en los sectores 4 (59%) y 5 (34%) (laterales) y el nervio ulnar en los sectores 2 y 3 (inferiores) en un 69% y un 24% de los casos, respectivamente. Hubo una considerable variación de la localización de los nervios con relación a los aspectos superior e inferior de la arteria.
CONCLUSIÓN: La inspección en tiempo real, por ultrasonido, de las estructuras neuro vasculares del plexo braquial en la axila mostró que los nervios mediano, ulnar y radial pueden presentar diferentes relaciones con la arteria axilar.
Several approaches to the brachial plexus are described within the techniques of Regional Blocks. The approach is chosen according to the location of the surgery in the upper limb. The axillary approach is indicated, especially, for surgeries in the forearm, wrist, and hand. Its success rate depends on the correct location of the nerves in relation to the anatomic references, adequate positioning of the needle, and dispersion of the local anesthetic around the nerves 1-3.
Classic anatomy books and several studies undertaken to evaluate the possible causes of failure used, in most cases, cadavers as anatomic models; however, there are differences in tone and rigidity of the structures in cadavers when compared with living structures. Besides, conservation methods might be responsible for distortion of those structures 4.
Taking those observations in consideration and knowing that few works have used ultrasound to identify anatomic structures involved in the brachial plexus in the axilla, the present study in healthy volunteers was undertaken to evaluate the position of the main nerves of the brachial plexus in the axilla in relation to the axillary artery.
After approval by the Ethics and Research Commission of the Hospital Governador Carlos Ramos, 30 volunteers of both genders, ages 18 to 67 years, physical status ASA I, gave their oral consent and were scheduled for ultrasound of the brachial plexus in the axilla.
For the exams, the arm was positioned according to the description of Winnie: patient in the supine position with the arm in a 90° abduction in relation to the trunk and forearm with a 90° flexion in relation to the arm and in external rotation.
The exam was done with a portable ultrasound device (Titan, Sonosite) with a 5 cm wide band (5-10 MHz) linear digital transducer and the images were stored in a memory card (compact flash).
The transducer was transversal to the skin in the axillary region, in the internal portion of the arm, and positioned until it showed the intersection of the pectoral major and biceps muscles. Individualization of the structures in the vascular-nerve plexus (Figure 1) was then initiated.
The exam was performed by two experienced anesthesiologists in ultrasound guided blocks, who identified the axillary artery and radial, median and ulnar nerves, recording their position.
To relate the nerves to the axillary arteries, the study region was divided in 8 sectors and placed in a circle with the artery in the center (Figure 2). A transparent sheet (16 ´ 20 cm) with the circle was used to record the results.
The transparency was placed on the screen of the ultrasound equipment so the center of the graphic corresponded to the axillary artery and the upper margin of the sheet was parallel to the upper margin of the screen. This was used to determine in which sector of the graphic each nerve was located.
The data were analyzed using descriptive statistics and expressed as percentages.
Twenty-nine volunteers were examined. Table I shows the demographic data. One patient refused to be examined and was excluded from the study.
The nerves were identified in every patient: median in sector 8 in 55% of the patients and in sector 1 in 28% (Figure 3); radial nerve in sector 4 in 59% of the patients and in sector 5 in 34% (Figure 4); and the ulnar nerve in sector 2 in 69% and in sector 3 in 24% (Figure 5).
The ultrasound has been considered an efficient method to identify nerve structures and it can be a powerful tool in peripheral blocks.
In this study, it was observed that the ultrasound was useful in identifying the terminal nerves of the brachial plexus in the axilla. When ultrasound is used in axillary brachial plexus blocks, the axillary artery, veins and muscles that surround the sheath of the nerve are visualized first. Afterwards, the nerve structures are identified, the needle is introduced, and the local anesthetic is deposited around each nerve. The transverse image of nerves in the ultrasound appear as hyperechoic nodules mixed with a hypoechoic tissue, as demonstrated by Silvestri et al. 5,6 For the effective blockade of the brachial plexus in the axillary region, the knowledge of the exact position of each nerves is necessary. The anatomic positions showed in textbooks are determined by dissecting cadavers. But, besides anatomic variations, there are differences between the cadaveric tissue and living tissue 14.
The present study, despite the small number of patients, demonstrated variations in the position of the radial, median and ulnar nerves in relation to the axillary artery. The impact of these variations for the clinical success of the blockades done by methods that depend on surface anatomical references, palpation, or fascial clicks is unknown. However, one cannot discard that this might contribute to possible failures in brachial plexus blocks.
Some studies propose the presence of septa dividing the brachial plexus in the axilla 3. In this study we used a high frequency (5 to 10 MHz) transducer, which allows the identification of nerve structures. However, it was not possible to identify the presence of sheath or septa in the brachial plexus.
To conclude, high-resolution ultrasound was capable of identifying the neurovascular structures in the axillary region of all patients, confirming the great variability in nerve position in relation to the axillary artery.
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04. Partridge BL, Katz J, Benirschke K Functional anatomy of the brachial plexus sheath: implication for anesthesia. Anesthesiology, 1987;66:743-747. [ Links ]
05. Silvestri E, Martinoli C, Derchi LE et al. Echotexture of peripheral nerves: correlation between US and histologic findings and criteria to differentiate tendons. Radiology, 1995;197:291-296. [ Links ]
06. Yang WT, Chui PT, Metreweli C Anatomy of the normal brachial plexus revealed by sonography and the role of sonographic guidance in anesthesia of the brachial plexus. AJR, 1998;171: 1631-1636. [ Links ]
Dr. Diogo Brüggemann da Conceição
Rua Bocaiúva, 1.659/1.103
88015-530 Florianópolis, SC
Submitted em 12
de dezembro de 2006
Accepted para publicação em 21 de agosto de 2007
* Received from Núcleo de Ensino e Pesquisa em Anestesia Regional do Hospital Governador Celso Ramos, CET Integrado de Anestesiologia da SES-SC, Florianópolis, SC