The cubital (antecubital) fossa is a triangular depression anterior to the elbow joint. Boundaries Contents The contents of cubital fossa from the medial to lateral side are easily recalled by the mnemonic MBBS (Figures 5.1 and 5.2). (M = Median nerve, B = Brachial artery, B = Biceps tendon, S = Superficial radial nerve) Describe the course of brachial artery in the antecubital fossa. The brachial artery normally bifurcates into radial and ulnar arteries in the apex of the fossa, although this bifurcation may occur much higher in the arm due to anatomical variation. Which vein would you choose for the insertion of a long line at the antecubital fossa? Where might the line ‘stick’ and how would you negotiate it? When placing a long line, the two main veins available in the antecubital fossa are the basilic and cephalic veins. The more medial basilic vein has a smoother and direct route to the subclavian vein. The lateral cephalic vein turns more sharply and passes through the clavipectoral fascia with valves present at its termination. These factors increase the risk of the long line not advancing into the subclavian vein when using the cephalic vein. If problems occur with advancing the line, abducting the arm to help straighten out its path might be useful. Flushing the line with saline can also help to advance a line through a valve that may be obstructing its passage. Can you describe the arterial supply to the upper limb, starting at the aorta? The subclavian artery originates from the aorta on the left and the brachiocephalic artery on the right. The subclavian artery becomes the axillary artery which then continues as the brachial artery. The brachial artery divides into the radial and ulnar artery at the antecubital fossa between the two heads of the biceps (Figure 5.3 and Table 5.1). Table 5.1 Arterial Supply of Upper Limb Axillary artery Course: formed at the lateral border of the first rib as a continuation of subclavian artery. It is deep to the pectoralis minor and has the cords of brachial plexus around it. It continues as the brachial artery at the lower border of the teres major muscle. Supply: shoulder, scapula, axilla, lateral thoracic wall and associated muscles Brachial artery Course: begins at the lateral border of axilla and runs medial to the biceps muscle towards the antecubital fossa where it bifurcates into the terminal branches – radial and ulnar arteries Supply: humerus, elbow and muscles of the arm Radial artery Course: descends from the antecubital fossa to the wrist along the lateral side of the forearm between the flexor carpi radialis and the brachialis. It crosses the anatomical snuff box on the dorsal aspect and enters the palm of the hand terminating as the deep palmar arch. Supply: elbow, muscles of the forearm and hand Ulnar artery Course: the ulnar artery descends along the medial side of the forearm alongside the ulnar nerve which lies lateral to it. It travels above the flexor retinaculum at the wrist and sends a branch to the deep palmar arch and terminates as the superficial palmar arch. Supply: elbow, muscles of the forearm and hand What are the indications for an arterial cannula? Blood pressure monitoring Blood sampling Interventional procedure Continuous cardiac output monitoring What might the contraindications be? Absolute contraindications Relative contraindications Which sites in the upper limb do you use for arterial cannulation? What are the site-specific disadvantages? The radial artery is commonly used as it has a fairly reliable anatomy, is easily palpated and visible with ultrasound guidance. However, it is more prone to occlusion and haematoma formation. The brachial or axillary artery is often used in paediatric/neonatal ICU but there is significant risk of distal ischaemia and compartment syndrome if there is an arterial occlusion due to the absence of collateral circulation. The ulnar artery is not routinely used in anaesthetics and there is a risk of ulnar nerve injury due to its close proximity. How would you site a radial arterial cannula? What are the possible complications? What is Allen’s test? How is it performed? Allen’s test is a non-invasive evaluation of the arterial patency of the hand which assesses the collateral arterial blood flow. It is done prior to any radial arterial intervention (radial artery harvesting for coronary artery bypass grafting or for forearm flap elevation) or diagnostic work up for thoracic outlet syndrome. The aim is to check the adequacy of blood flow from the ulnar artery in the event of radial artery occlusion following the procedure. The original Allen’s test tests both hands at the same time. A modified Allen’s test is currently used which tests one hand at a time. In a negative (normal) Allen’s test, the hand will flush in 5–15 seconds indicating that the ulnar artery has a good flow. In a positive (abnormal, positive = persistent pallor) Allen’s test, the time to reperfusion is >15 seconds suggesting that the ulnar circulation is inadequate, in which case, the radial artery should not be cannulated. What is Volkmann’s ischaemic contracture? The permanent contraction of the flexor compartment at the level of the wrist due to obstruction of the brachial artery is called Volkmann’s ischaemic contracture. The claw-like deformity occurs due to ischaemia and necrosis of the flexor digitorum profundus and the flexor pollicis longus. Causes include supracondylar fractures, prolonged upper arm tourniquet time, compression from a plaster cast, compartment syndrome and accidental intra-arterial injection of drugs. What is the management of inadvertent intra-arterial injection? Intra-arterial injection of drugs may cause acute, severe extremity ischaemia and gangrene and the main priority is to maintain distal perfusion. The drugs which cause the most severe ischaemia and tissue death are barbiturates, ketamine and phenytoin, whilst propofol, atracurium, rocuronium and amiodarone can also cause ischaemia. The steps in the pathophysiology are arterial spasm, direct tissue destruction by the drug and subsequent chemical arteritis leading to endothelial destruction. With certain drugs such as thiopentone, precipitation and crystal formation within the distal microcirculation lead to ischaemia and thrombosis. Management General measures Specific measures The venous drainage of the upper limb can be divided into the superficial and the deep system. The superficial venous system lies in the subcutaneous tissue and drains into the deep venous system via perforating veins. Superficial venous system Deep venous system When attempting venepuncture at the antecubital fossa, which structure in particular provides a degree of protection to the brachial artery? The bicipital aponeurosis separates the brachial artery (which lies beneath the aponeurosis) from median cubital vein thereby preventing inadvertent arterial puncture during median cubital vein cannulation. Which superficial nerves are at risk during attempted venous cannulation at the elbow? Medial, lateral and posterior cutaneous nerves of the forearm. How can the veins of the upper limb be used to provide central venous access? Peripherally inserted central catheters (PICC) can be inserted into the upper limb using the Seldinger technique via a needle. The catheter passes through the skin and into the superior vena cava. It can be placed under ultrasound guidance or with a contrast venogram. It is an excellent method of providing medium-term venous access (e.g. feeding lines in paediatrics, long-term intravenous antibiotics). The upper limb is divided into the shoulder, arm (between shoulder and elbow), forearm (between elbow and wrist) and hand. The axilla, cubital fossa and carpal tunnel are important areas of transition in the upper limb. Figures 5.5 and 5.6 show the dermatomal and peripheral nerve distribution of the anterior and posterior aspects of the upper limb. What movements are provided by the myotomes of the upper limb? A complex neural network in the neck and axilla that starts from the intervertebral foramina, passes between scalenus anterior and medius, into the posterior triangle of the neck, behind the clavicle, over the first rib, posterolateral to the subclavian artery and into the axilla. The major nerves of the brachial plexus carry motor and sensory function and it is important to note that the sensory distribution from the peripheral nerves is different from the dermatomes (Table 5.2). Table 5.2 Functional Importance of Brachial Plexus Sensory innervation of the upper limb and most of the axilla – except for an area in the medial upper arm supplied by the intercostobrachial nerve. This is often the origin of tourniquet pain. Motor innervation to the upper limb and shoulder girdle – except for trapezius, which is innervated by the 11th cranial nerve Autonomic innervation to the upper limb, by communicating with the stellate ganglion at T1 Course of the brachial plexus through the neck, demonstrating its relations to the scalene muscles, subclavian artery and clavicle (Figure 5.7).
Upper Limb
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Structures
Circulation
Nervous System
Structures
Antecubital Fossa
Bibliography
Circulation
Arterial Supply of Upper Limb
Venous Drainage of Upper Limb
Bibliography
Nervous System
Dermatomes and Peripheral Nerve Distribution
Brachial Plexus
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