Chapter 17: Vascular access devices: insertion and management
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Anatomy and physiology
Anatomy of veins
Veins consist of three layers.
Tunica intima
The tunica intima is a smooth endothelial lining that allows the passage of blood cells (Jenkins and Tortora [230]). If it becomes damaged, the lining may become roughened and there is an increased risk of thrombus formation (Hadaway [194], Scales [400]). Within this layer are thin folds of endothelium called valves (flap‐like cusps), which keep blood moving towards the heart by preventing backflow (Jenkins and Tortora [230]). Valves are present in larger vessels and at points of branching, and can be seen as noticeable bulges in the veins (Weinstein and Hagle [465]).
Tunica media
The middle layer of the vein wall is composed of muscular tissue and nerve fibres, both vasoconstrictors and vasodilators, which can stimulate the vein to contract or relax. This layer is not as strong or stiff as in an artery and therefore veins can distend or collapse as the pressure rises or falls (Jenkins and Tortora [230]). Stimulation of this layer by a change in temperature (cold) or by a mechanical or chemical stimulus can produce venous spasm, which can make insertion of a needle more difficult.
Tunica adventitia or externa
The tunica adventitia (also known as the tunica externa) is the tough outer layer and consists of connective tissue, which surrounds and supports the vessel (Tortora and Derrickson [444]).
Anatomy of arteries
Arteries tend to be placed more deeply than veins and can be distinguished by their thicker walls (which do not collapse), the presence of a pulse and bright red blood. It should be noted that aberrant arteries may be present. These are arteries that are located superficially in an unusual place (Jenkins and Tortora [230]).
There are two main types of arteries – muscular and elastic – and they are composed of three layers:
- the tunica intima, which has elongated endothelial cells
- the tunica media, which in elastic arteries is thicker, with more elastic and fibrous tissue arranged in circular bands, while in muscular arteries it is a large mass of smooth muscle fibres that control constriction and relaxation
- the tunica adventitia, which contains both collagen and elastic fibres, nerve bundles and lymphatic vessels (Tortora and Derrickson [444]).
Veins of the peripheral circulation
The superficial veins of the upper limbs are most commonly chosen for cannulation and insertion of midlines and peripherally inserted central catheters (PICCs). These veins are numerous and accessible, which ensures that the procedure can be performed safely and with minimum discomfort (Garza and Becan‐McBride [171], Hoeltke [215]). They are:
- the cephalic vein
- the basilic vein
- the metacarpal veins (used only when the others are not accessible) (Figure 17.1).
Figure 17.1 (a) Superficial veins of the forearm. (b) Superficial veins of the dorsal aspect of the hand. (c) Central veins and veins of the upper arm.
On the lateral aspect of the wrist, the cephalic vein rises from the lateral aspect of the dorsal venous network of the hand and flows upwards along the radial border of the forearm as the median cephalic, crossing the antecubital fossa as the median cubital vein (Jenkins and Tortora [230]). Care must be taken to avoid accidental arterial puncture, as this vein crosses the brachial artery (Jenkins and Tortora [230]). It is also in close proximity to the radial nerve (Dougherty [124], Jenkins and Tortora [230], Masoorli [300]).
The basilic vein begins on the medial aspect of the dorsal venous network of the hand and ascends the forearm and antemedial surface of the arm (Jenkins and Tortora [230]). It may be prominent but is not well supported by subcutaneous tissue, which makes it roll easily. Owing to its position, a haematoma may occur if the patient flexes the arm on removal of the needle, as this squeezes blood from the vein into the surrounding tissues (McCall and Tankersley [303], Weinstein and Hagle [465]). Care must also be taken to avoid accidental puncture of the median nerve and brachial artery (Garza and Becan‐McBride [171]).
The metacarpal veins are easily visualized and palpated. However, the use of these veins is contraindicated in the elderly, where skin turgor and subcutaneous tissue are diminished (Weinstein and Hagle [465]).
Veins of the central venous circulation
A central vein is one near the centre of the circulation: the heart (Chantler [69]). Those more commonly used for central venous catheterization are the internal jugular, subclavian and femoral veins (Figure 17.2). The internal jugular vein emerges from the skull through the jugular foramen and runs down the neck into the carotid sheath (Farrow et al. [144], Tortora and Derrickson [444]). The axillary vein is a continuation of the basilic vein. From the lateral edge of the ribs to the sternal edge of the clavicle, the continuation of the axillary becomes the subclavian. It angles upwards as it arches over the first rib and passes under the clavicle, forming a narrow passage for the vein (Galloway and Bodenham [165], [166], Hadaway [194]). Here it joins the internal jugular vein to form the brachiocephalic vein behind the sternoclavicular joint. The left brachiocephalic vein is 6 cm in length, twice as long as the right (Hadaway [194], Jenkins and Tortora [230]).
Figure 17.2 The main veins used for central venous access device placement. Source: Reproduced from Dougherty ([123]) with permission of John Wiley & Sons.
The superior vena cava (SVC) drains venous blood from the upper half of the body and is formed from the confluence of the two brachiocephalic (innominate) veins (2 cm wide) (Farrow et al. [144]). The SVC is 7 cm long in normal adults and descends vertically to the upper part of the right atrium of the heart (Farrow et al. [144]).
The femoral vein drains the majority of blood from the lower limb and enters the thigh as a continuation of the popliteal vein. It ascends through the thigh and becomes the external iliac vein and drains into the inferior vena cava. The inferior vena cava drains the lower half of the body and is formed by the two common iliac veins (Jenkins and Tortora [230]).
