VENOUS CANNULATION

© 2004 The Medicine Publishing Company Ltd2ANAESTHESIA AND INTENSIVE CARE MEDICINE

The three types of veins in the lower limb are superficial, deep and communicating (perforating). Valves are present in all the larger vessels including the communicating veins.

Superficial veinsThe superficial veins drain the subcutaneous tissue and termi-nate in the two large longitudinal channels, the great and the small saphenous veins. In the foot, the superficial veins drain into dorsal and plantar venous arches from which originate the two long veins.

The great (or long) saphenous vein originates from the medial side of the dorsal venous arch beginning just in front of themedial malleolus. It ascends the medial side of the calf and thigh (accompanied in the calf by the saphenous nerve) and passes through the saphenous opening of the deep fascia 1.5 cm belowthe inguinal ligament to enter the femoral vein. Its tributaries drain the leg, thigh, inguinal region and pubic region but its most clini-cally important branches are the several communicating branches (or perforating veins) that drain from it into the deep veins of the calf and thigh, perforating the deep fascia generally on the medial side of the leg (Figure 1). The venous valves ensure that blood flow is from superficial to deep veins and once within the deep fascia, calf muscle contraction propels the blood heartwards. The constancy of the great saphenous vein’s position anterior to the medial malleolus is of considerable importance. It provides a certain point of access should urgent intravenous transfusion be necessary.

The small (or short) saphenous vein originates from the lateral end of the dorsal venous arch. It ascends behind the lateral mal-leolus along the back of the calf to end by piercing the deep fascia a variable distance below the popliteal fossa to end in the popliteal vein. In its lower course it is accompanied by the sural nerve. It has tributaries communicating with the deep veins of the calf and one or more that join with the great saphenous nerve (Figure 2).

The deep veinsThe deep veins comprise the soleal plexus, the popliteal and the femoral veins. They communicate with the superficial veins by ‘perforators’, veins that perforate the deep fascia (Figure 1),

the valves of which are arranged to allow blood to flow onlytowards the deep veins. The soleal plexus, which lies within the muscles of the calf, drains into the popliteal vein and that into the femoral vein, which both accompany their corresponding artery deep to the deep fascia. The soleal plexus has a large volumeand it is the pressure of the contracting calf muscles (the soleal pump) that is an important factor in ensuring venous return from the lower limb to the heart. The soleal pump depends for its efficiency on the competence of the valves in the communicating veins.

The femoral triangleThe femoral triangle is a triangular fascial space in the supero-medial third of the thigh. It is bounded above by the inguinalligament, medially by adductor longus and laterally by sartorius.Its floor is formed by iliopsoas, pectineus and adductor longus and its roof by the fascia lata, which is pierced by the saphenousopening that conveys the saphenous vein. Over its roof lie the superficial inguinal lymph nodes and branches of the saphenous vein. The triangle contains, from medial to lateral, the femoral nerve, femoral artery, femoral vein. The artery and vein enter beneath the inguinal ligament, enclosed in a fascial femoral sheath (Figure 3),

The veins of the lower limbJohn Craven

John Craven was formerly Consultant Surgeon at York District Hospital,

York, UK. He trained in Manchester, Uganda and Cardiff. He is past

chairman of the primary examiners of the Royal College of Surgeons of

England.

The great saphenous vein and calf perforators

Perforator below knee

Great saphenous

Perforator

Perforator

Perforator

Posterior arch vein

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VENOUS CANNULATION

© 2004 The Medicine Publishing Company Ltd3ANAESTHESIA AND INTENSIVE CARE MEDICINE

which is continuous with the extraperitoneal fascia of the abdo-men. The sheath’s medial part contains a small gap, about 1 cm long, the femoral canal, which is a potential site for the develop-ment of a femoral hernia. The canal is bounded by the inguinal ligament above, the pectineal part of the inguinal ligament medi-ally, the femoral vein laterally and the periosteum of the superior pubic ramus inferiorly. The femoral artery is palpable within the triangle beneath the midpoint of the inguinal ligament and the femoral vein lies, impalpable, but accessible for venous access, on its medial side. The superficial lymph nodes over the triangle accept thedrainage of the lower abdominal wall, the perineum and the lower leg.

Deep vein thrombosis The soleal plexus is the most common site of origin of a deep vein thrombosis. Immobility increases the stagnation of blood in the lower limb especially in the soleal plexus and it is there that the venous thrombosis begins. The thrombus may then extend into the popliteal and femoral veins and it is then that the risk of pul-monary embolism becomes significant. Thrombosis in the soleal plexus may also extend into the perforating veins and subsequently, after spontaneous recanalization, the protective valves in those

Short saphenous vein entering popliteal vein (deep fascia has been incised)

Popliteal vein

Deep fascia

Popliteal fossa

Posterior arch vein

Short saphenous vein

Lateral malleolus

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vessels are destroyed which then allows the venous blood to travel retrogradely, from the deep veins to the superficial, resulting in obvious varicose veins. This, in turn, results in venous hyperten-sion in the superficial tissues of the leg as shown by soft tissue fibrosis, hyperpigmentation and, in severe cases, in chronic skin ulceration. It is thought that the primary cause of varicose veins is the incompetence of the valves in the perforating veins, and the retrograde flow that follows produces distension of the superficial veins. This, in turn, distends the saphenous veins and renders their valves incompetent.

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Femoral triangle

lliopsoas muscle

Psoas sheath

Femoral nerve

Femoral artery

Femoral vein

Lymph node

Femoral canal

Femoral sheath

Pubic tubercle

Fascia lata

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