The Royal Marsden Hospital Manual of Clinical Nursing Procedures - Lisa Dougherty [407]
Table 11.1 Types of organisms
Organism Definition
Aerobic Aerobic bacteria will only grow in the presence of oxygen
Anaerobic Anaerobic bacteria prefer an atmosphere of reduced oxygen, such as deep in wound bed tissue and facultative anaerobes can grow in either the presence or absence of oxygen
Bacteria Bacteria are unicellular organisms that multiply and die very rapidly, especially once removed from their optimum environment
Virus Viruses are intracellular parasites that hijack the genetic material of the host cell, and are therefore unable to multiply outside living cells
Gould and Brooker (2008), Higgins (2007), Winter 2005.
The sooner a specimen arrives in the laboratory, the greater the chance of organisms being identified. Some pathogens do not survive once they have left the host, whilst normal body flora within the sample may proliferate and overgrow, inhibiting or killing the pathogen (Weston 2008).
If delays are anticipated, samples need to be stored appropriately, depending on the nature of the specimen, until they can be processed. For example, blood cultures need to be incubated at 37°C, whereas swabs must be either refrigerated or kept at ambient temperature, depending on the site from which they were taken.
The transport of clinical specimens must conform to health and safety legislation and regulations, and there are more specific guidelines on the labelling, transport and reception of specimens within clinical laboratories and similar facilities (HSE 2003).
Blood: obtaining samples from a peripheral vein (venepuncture)
Definition
Venepuncture is the procedure of entering a vein with a needle (Weller 2009).
Anatomy and physiology
The superficial veins of the upper limb are most commonly chosen for venepuncture. These veins are numerous and accessible, ensuring that the procedure can be performed safely and with minimum discomfort (Ernst 2005). In adults, veins located on the dorsal portion of the foot may be selected but there is an increased risk of deep vein thrombosis (Garza and Becan-McBride 2010) or tissue necrosis in diabetics (Ernst 2005). Therefore, veins in the lower limbs should be avoided where possible.
Vein choice
The veins commonly used for venepuncture are those found in the antecubital fossa because they are sizeable veins capable of providing copious and repeated blood specimens (Weinstein and Plumer 2007). However, the venous anatomy of each individual may differ. The main veins of choice are the (Figure 11.1):
Figure 11.1 (a) Superficial veins of the forearm. (b) Superficial veins of dorsal aspect of the hand.
Reproduced with permission from Becton Dickinson and Company.
median cubital veins
cephalic vein
basilic vein
metacarpal veins (used only when the others are not accessible).
Median cubital vein
The median cubital vein may not always be visible, but its size and location make it easy to palpate. It is also well supported by subcutaneous tissue, which prevents it from rolling under the needle.
Cephalic vein
On the lateral aspect of the wrist, the cephalic vein rises from the dorsal veins and flows upwards along the radial border of the forearm as the median cephalic, crossing the antecubital fossa as the median cubital vein. Care must be taken to avoid accidental arterial puncture, as this vein crosses the brachial artery. It is also in close proximity to the radial nerve (Dougherty 2008, Masoorli 2002).
Basilic vein
The basilic vein, which has its origins in the ulnar border of the hand and forearm (Marieb and Hoehn 2010), is often overlooked as a site for venepuncture. It may well be prominent but is not well supported by subcutaneous tissue, making it roll easily, which can result in difficult venepuncture. Owing to its position, a haematoma may occur if the patient flexes the arm on removal