The Royal Marsden Hospital Manual of Clinical Nursing Procedures - Lisa Dougherty [419]
Legal and professional issues
Competencies
Blood cultures should be collected by practitioners who have been trained in the collection procedure and whose competence in blood culture collection has been assessed (DH 2007a). Practitioners must be competent and feel confident that they have the knowledge, skill and understanding to undertake blood culture sampling for microbiological analysis (NMC 2008a).
Preprocedural considerations
Equipment
The use of a needle to decant blood into the culture bottles is now largely redundant due to the wide use of closed, vacuumed blood collection systems (for example, Bio-Merieux BacT/ALERT® system which utilizes either a holder for venous access device sampling or a Luer adaptor safety winged device for peripheral sampling). See Figure 11.2. This reduces the health and safety risk to the healthcare professional and the risk of culture contamination.
Figure 11.2 A vacuumed collection system: two blood culture bottles, Vacutainer holder® and Vacutainer ‘butterfly’®.
However, if the use of the needle and syringe method is unavoidable, the needle should not be changed between sample collection and inoculation of blood into the culture bottles (DH 2007a). Care should be taken not to under- or overfill the bottles as it is difficult to accurately judge the sample volume with this method (Shore and Sandoe 2008).
Volume of blood culture specimen collection
The volume of blood taken for a culture is also critical to ensure correct blood to liquid culture medium ratio. A false-negative result could occur if an insufficient volume is introduced or if too much blood is introduced, due to the effect of the culture medium in the bottles being diluted (Higgins 2007). The liquid culture medium is a mixture of nutrients that supports microbial growth and inhibits phagocytosis and lysozyme activity (Shore and Sandoe 2008). This helps to determine if there are pathogenic micro-organsims present in the blood. As there are a number of systems in use, the manufacturer’s instructions should be followed as to the total volume required for each bottle. Adult patients with clinically significant bacteraemias often have a low number of colony-forming units per millilitre of blood and a minimum of 10 mL per culture bottle is recommended (Dellinger et al. 2008).
Non-pharmacological support
Skin preparation products
Poor aseptic technique and skin decontamination can cause contamination of a blood culture with the patient’s own skin flora, such as coagulase-negative staphylococci (Weston 2008). A combination of 2% chlorhexidine gluconate in 70% isopropyl alcohol is recommended as being effective for skin antisepsis (DH 2007a, Madeo and Barlow 2008, Pratt et al. 2007). Chlorhexidine gluconate maintains a persistent antimicrobial function by disrupting the cell membrane and precipitating their contents, whilst the isopropyl alcohol quickly destroys micro-organisms by denaturing cell proteins (Inwood 2007). In order to achieve a reduction and inhibition of the micro-organisms living on the skin, gentle friction is required for 30 seconds and the solution should be allowed to dry to achieve good skin antisepsis and to expose the cracks and fissures of the skin to the solution (Pratt et al. 2007).
Central venous access device-related infection
A CVAD presents a high risk of infection with an incidence of bacteraemia of between 4% and 8% (HPA 2008f). When it is suspected that the CVAD is the source of infection, a blood culture sample should ideally be obtained from each lumen of the vascular device, as well as obtaining a peripherally drawn sample (Dellinger et al. 2008, DH 2007a, Gabriel 2008). Adequate hub cleansing with 2% chlorhexidine in 70% isopropyl alcohol is essential in reducing cross-contamination of the sample (Inwood 2007).
Blood cultures from a CVAD can identify colonization from either the device itself or the bloodstream (Penwarden and Montgomery 2002). To diagnose CVAD-related infections,