The Royal Marsden Hospital Manual of Clinical Nursing Procedures - Lisa Dougherty [408]
Metacarpal veins
The metacarpal veins are easily visualized and palpated. However, the use of these veins is contraindicated in the elderly in whom skin turgor and subcutaneous tissue are diminished (Weinstein and Plumer 2007).
Layers of the vein
Veins consist of three layers: the tunica intima, the tunica media and the tunica adventitia.
Tunica intima
The tunica intima is a smooth endothelial lining, which allows the passage of blood cells. If it becomes damaged, the lining may become roughened, leading to an increased risk of thrombus formation (Weinstein and Plumer 2007). Within this layer are folds of endothelium called valves, which keep blood moving towards the heart by preventing backflow. Valves are present in larger vessels and at points of branching and are seen as noticeable bulges in the veins (Weinstein and Plumer 2007). However, when suction is applied during venepuncture, the valve can compress and close the lumen of the vein, thus preventing the withdrawal of blood (Weinstein and Plumer 2007). Therefore, if detected, venepuncture should be performed above the valve in order to facilitate collection of the sample (Weinstein and Plumer 2007).
Tunica media
The 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 an artery and therefore veins can distend or collapse as the pressure rises or falls (Waugh et al. 2006, Weinstein and Plumer 2007). Stimulation of this layer by a change in temperature, mechanical or chemical stimulation can produce venous spasm, which can make a venepuncture more difficult.
Tunica adventitia
The tunica adventitia is the outer layer and consists of connective tissue, which surrounds and supports the vessel.
Arteries tend to be placed more deeply than veins and can be distinguished by the thicker walls, which do not collapse, the presence of a pulse and the bright red blood. It should be noted that aberrant arteries may be present; these are arteries located superficially in an unusual place (Weinstein and Plumer 2007).
Choosing a vein
The choice of vein must be that which is best for the individual patient. The most prominent vein is not necessarily the most suitable vein for venepuncture (Weinstein and Plumer 2007). There are two stages to locating a vein:
1 visual inspection
2 palpation.
Visual inspection
Visual inspection is the scrutiny of the veins in both arms and is essential prior to choosing a vein. Veins adjacent to foci of infection, bruising and phlebitis should not be considered, owing to the risk of causing more local tissue damage or systemic infection (Dougherty 2008). An oedematous limb should be avoided as there is danger of stasis of lymph, predisposing to such complications as phlebitis and cellulitis (Hoeltke 2006, Smith 1998). Areas of previous venepuncture should be avoided as a build-up of scar tissue can cause difficulty in accessing the vein and can result in pain due to repeated trauma (Hoeltke 2006).
Palpation
Palpation is an important assessment technique, as it determines the location and condition of the vein, distinguishes veins from arteries and tendons, identifies the presence of valves and detects deeper veins (Dougherty 2008). The nurse should always use the same fingers for palpation as this will increase sensitivity and the ability of the nurse to know what they are feeling. The less dominant hand should be used for palpation so that in the event of a missed vein the nurse can repalpate and realign the needle (Hoeltke 2006). The thumb should not be used as it is not as sensitive and has a pulse, which may lead to confusion in distinguishing veins from arteries in the patient (Weinstein and Plumer