CliniCal anaesthesia

The thoracic inlet and first ribJohn Craven

Abstractthe anatomy of the thoracic inlet is described in this article with special

reference to those features important for the safe and successful tech-

nique of percutaneous catheterization of the subclavian vein.

Keywords first rib; sternoclavicular joint; subclavian artery;

subclavian vein

The thoracic inlet, small and kidney-shaped, is about 10 cm wide, but only 5 cm anteroposteriorly. It slopes forwards and is bounded by the first thoracic vertebra posteriorly, the upper border of the manubrium anteriorly, and the first rib and costal cartilage laterally. It transmits the oesophagus, the trachea and the large vessels. These comprise the right and left subclavian arteries and the right and left brachiocephalic veins, which unite behind the lower border of the right first costal cartilage to form the superior vena cava (Figure 1). Lying on the anterior surface of the neck of the first rib is the sympathetic trunk. On each side is the apex of the lung rising some 3 cm above the medial third of the clavicle and covered by the dome of the pleura.

John Craven, FRCS, was formerly Consultant Surgeon at York Hospital,

York. He is past chairman of the primary examiners of the Royal

College of Surgeons of England.

The thoracic inlet

Dome of pleura

Brachial plexus

Subclavian artery

Subclavian vein

Superior vena cava

Scalenus anterior

Phrenic nerve

Thoracic duct

Oesophagus

Trachea

First rib

Figure 1

anaesthesia anD intensiVe CaRe MeDiCine 8:12 49

The subclavian arteries commence behind the sternoclavicu-lar joint and curve laterally in front of the apex of the lung before passing onto the upper surface of the first rib. Both subclavian veins lie anterior to their respective arteries, curving medially from the middle third of the clavicle to form the brachiocephalic vein by joining their internal jugular vein behind the sterno-clavicular joint.

The first rib (Figure 2) is the shortest, strongest, broadest and most curved rib. It lies in an oblique plane, sloping forwards and downwards and forms the junction between the the roof of the thoracic cavity and the root of the neck. It possesses a small head that articulates with the body of the first thoracic vertebra, a rounded neck, a posterior tubercle and a body. The anterior end of the body bears the costal cartilage, which articulates with the manubrium. The lower surface of the body is smooth and lies on the pleura. A small scalene tubercle on its medial border marks the attachment of the scalenus anterior muscle. This tubercle, on the upper surface of the body separates an anterior groove for the subclavian vein from a posterior groove for the subclavian artery and the lower trunk of the brachial plexus, which lies behind the artery (the nerve fibres in contact with the rib are all derived from T1). Scalenus medius is attached to the upper surface of

Upper surface of the first rib

First thoracic

nerve (upper

branch)

Highest

intercostal

artery

Sympathetic

trunk

Scalenus posterior

Scalenus medius

Subclavian artery

Serratus anterior

Scalenus anterior

Subclavian vein

Costoclavicular ligament

Posterior

Anterior

Figure 2

Infraclavicular access to the large veins

Clavicle

Entry site

Subclavian vein

entered above first rib

First rib

Direction

of needle

Jugular notch

Figure 3

7 © 2007 elsevier ltd. all rights reserved.

CliniCal anaesthesia

the body behind the groove for the artery. Anterior to the neck of the rib and behind the pleura lie, from medial to lateral, the sympathetic trunk and the large branch of the first thoracic nerve to the brachial plexus.

The subclavian veins are in a very superficial and constant position, which allows easy percutaneous access to them; they may be catheterized for intravenous feeding or monitoring of the central venous pressure or used as a conduit for cardiac pacing

anaesthesia anD intensiVe CaRe MeDiCine 8:12 49

wires. The infraclavicular approach is preferred because there is less chance of accidental puncture of the pleura by this route. The needle is inserted one finger’s width below the midpoint of the clavicle and directed medially and as far anteriorly as pos-sible (to ensure that neither the pleura nor the subclavian artery is pierced) toward the jugular notch of the manubrium. The sub-clavian vein should be entered as it curves over the body of the first rib (Figure 3). ◆

8 © 2007 elsevier ltd. all rights reserved.