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Reducing the risks of device-related infection caused by staphylococci

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Intravenous (IV) therapy is a common and frequently essential intervention for patients undergoing medical care. Although this may have a positive effect on the health of the person in receipt of such therapy, it is not without risk. Any breach in the integrity of the skin, caused by wounds, incisions, or the use of penetrating devices such as intravascular catheters, can act as a portal for access to normally sterile tissues by micro-organisms and thereby predispose the patient to infection.

Patients receiving IV therapy are four times more susceptible to health-care-associated bacteraemia than those not receiving this form of intervention (Elliott, 1993). The increasing use of intravascular devices throughout medicine has been accompanied by significant morbidity and mortality associated with catheter-related sepsis (Waghorn, 1994). This paper will examine aspects of care that may reduce the risk of infection and describe the pathogens responsible for the majority of bacteraemia in the cannulated patient.

Interest in this form of infection has increased recently. Bacteraemia has now become the focus of political attention due to the perceived problem of health-care-associated infection (Public Health Laboratory Service, 2002). Because of the increase in media interest in health-care-associated infection, there is a perception that these types of infection are increasing. It is not possible to state whether this is true, however, as all surveillance until mandatory bacteraemia surveillance began in 1991 has been voluntary. Therefore it is not possible to state whether any increase is an actual one or is a result of better reporting. This will remain the case until the results of the mandatory surveillance have begun to produce trends that may be analysed.

A national surveillance scheme for reporting Methicillin-sensitive Staphylococcus aureus (MSSA) and Methicillin-resistant S. aureus (MRSA) has now been established in the UK since April 2001 (Barrett and Spencer, 2002). This requires NHS trusts to supply data on numbers of episodes of these specific types of bacteraemia, on the basis of which a rate per 1000 bed days is calculated using bed occupancy data. The results are in the public domain and are published on the PHLS website (www.phls.org.uk). The results ranged from 0 to 0.72 cases per 1000 bed days.

MRSA bacteraemia was chosen as a measure because it is relatively easy to extract the data - most isolates are indicative of infection and it is associated with a higher death rate than the sensitive strains of S. aureus (Whitby et al., 2001). Bacteraemia rate, however, may not be used as an indication of high overall levels of MRSA infection, and some authors have argued that other factors may be implicated in the rate of MRSA bacteraemia (Gray and George, 2001).

Device-related bacteraemia

The three leading pathogens that cause hospital-acquired bacteraemia in the UK are S. aureus, coagulase-negative staphylococci and Escherichia coli. The organisms responsible for infections that can occur in different devices in acute trusts in England are listed in Table 1 (Coello et al, 2003).

In the case of central venous catheter infections, Table 1 shows that staphylococci are responsible for over 68% of these, while in the case of peripheral catheter infections in excess of 69% of isolates are from this group of organisms.

Staphylococci

Staphylococci are gram-positive bacteria that are commensal flora on some parts of the body and are commonly found on the skin. Some staphylococci are pathogens and others have the potential for pathogenicity in the compromised host. The most common of the group implicated in IV device-related infections are coagulase-negative staphylococci such as S. epidermidis. Coagulase is an enzyme produced by S. aureus and is a confirmatory test commonly carried out in pathology laboratories when this type of infection is suspected. Although coagulase-negative staphylococci are of relatively low virulence, they have the same abilities of adhesion to foreign bodies and implants as other more pathogenic staphylococci, making it difficult to treat an infected line without first removing the colonised device.

S. aureushas other abilities that make it a significant pathogen in IV therapy, including phagocytic and toxic-shock-inducing toxins. The production of the enzyme coagulase changes fibrinogen into fibrin, which forms a protective barrier around the invading bacterium, preventing penetration by the body’s natural defences and any systemic form of treatment.

Treatment of staphylococcal episodes will depend on the type of incident, as well as the causative organism. Simple uncomplicated line colonisation with coagulase-negative staphylococci can be treated by simply removing the line, whereas S. aureus bacteraemia will require systemic antibiotic therapy with flucloxacillin in the case of methicillin-sensitive strains and glycopeptides for treatment of MRSA.

Pathogenesis of infection

There is evidence to show correlation between the skin flora colonising the catheter site with those causing bloodstream infection (Maki, 1991). Although this may seem to indicate that many IV exit site infections are endogenous in origin, cross-contamination during insertion may mean that the patient has acquired the infection exogenously (Maki, 1991). It is therefore crucial to reduce the potential for bacterial colonisation at the catheter exit site.

Staphylococci can also access the bloodstream by other means. MRSA colonisation of chronic wounds such as ulcers has been suggested as a predisposing factor for MRSA bacteraemia (Roghmann et al, 2001), although the study also identified that these patients were also more likely to have a central venous catheter, which could also have increased the risk.

Of the other groups of organisms affecting the cannulated patient, gram-negative organisms such as the acinetobacter spp and enterobacter spp have been implicated with the use of IV heparin infusions through extrinsic contamination and manipulation (Playford et al, 1999).

Coello et al’s (2003) paper examines the sources of device-related bacteraemia in English hospitals. Their paper looks at the potential for preventing bacteraemia with reference to national surveillance data; they note that the source of the reported bacteraemia is unreported in one-quarter of bacteraemias - thus, the results show that only a minimal of bacteraemias appear to be preventable. Further information would improve the potential for discovering the potential to prevent such infections.

Clinical infection relating to IV lines

Localised infection

The presence of erythema, oedema and a purulent exudate is indicative of infection. The patient may describe local pain and tenderness. Erythema and cellulitis may be present along the length of the subcutaneous track in tunnelled lines.

Occasionally, patients may experience pyrexia and thrombophlebitis may also be evident in the vessel associated with the device (Box 1).

Systemic infection

Bacteraemia may be described as the presence of micro-organisms in the bloodstream; a significant bacteraemia is one that exhibits clinical signs such as pyrexia, rigors and a raised white blood count.

Although a patient may have bacteraemia, the presence of infections is not always clinically obvious. A common pathogen that affects IV lines is S. epidermidis, a relatively low-virulence but highly resistant pathogen. In these cases the patient will exhibit a low-grade pyrexia that will be unaffected by antibiotics. Suspicion of systemic infection is confirmed by blood culture, with specimens being obtained from the line and a separate peripheral venepuncture.

Intravenous devices and bacteraemia

Any form of parenteral therapy requires a portal of entry to gain access to the cardiovascular system. However, this will breach body defences in the form of intact skin and will invade normally sterile tissues. Although the breach does increase the risks for patients, aspects of patient management that carry risk of infection can be adapted to reduce potential risk.

Insertion of a device

The procedure to insert an indwelling IV device must be carried out following the strict principles of asepsis. These should be related to the risk presented by the type of device and the proposed duration of insertion. Protective clothing will protect both parties, safeguarding the practitioner from blood-borne viruses and minimising the risk of cross-infection to the patient. In the case of a centrally placed longer-term device, the level of protection should be high, with the use of sterile barrier clothing and drapes, while for the insertion of a peripheral short-term device disposable non-sterile gloves are sufficient (O’Grady et al, 2002).

Skin cleansing prior to insertion

The patient’s skin needs to be thoroughly disinfected before a device is inserted to minimise the risk of contaminating the device. Alcoholic chlorhexidine is a suitable substance to use for this (Pratt et al, 2001).

Duration of insertion and documentation

Peripheral devices

In the UK, 48 hours is the accepted duration of peripheral cannulation (Elliot, 1993). Guidance from the USA (O’Grady et al, 2002), however, suggests that to prevent phlebitis peripheral venous catheters should be replaced in adults at least every 72-96 hours (Lai, 1998). The same guidance suggests that, in children, peripheral venous catheters should be left in place until IV therapy has been completed, unless complications, such as phlebitis and infiltration, occur (Shimandle et al, 1999).

It is possible to argue that this principle may be extended to all in receipt of this form of peripheral therapy, as long as monitoring is satisfactory, although nurses’ documentation of the insertion and removal of cannulas has been found to be unsatisfactory (Lundgren et al, 1996). This is supported by studies demonstrating that wards with specific IV documentation have been found to be associated with fewer complications (Smith et al, 1996).

Central devices

The current consensus remains that, while centrally placed devices are free from complications, they should be left in place. Care of the exit site may therefore be more important in the case of a centrally placed device, owing to its potential for a long periods of use (Elliott, 1993). Pulmonary arterial lines may be replaced after seven days and peripheral arterial catheters should be replaced every four to five days (Raad et al, 1993).

Catheter administration hubs

The administration hub is often one of the most frequently manipulated part of the IV line and thus gives the potential for contamination. Before any manipulation, the external surfaces of the hub should be disinfected with povidone-iodine or chlorhexidine gluconate (Pratt et al, 2001). However, some studies have not demonstrated a link between hub contamination and catheter colonisation (Lucet et al, 2000).

Choice of entry site dressing

Protection of the entry-site requires consideration. The purpose of an exit-site dressing is to prevent trauma to the wound and device, and to prevent extrinsic contamination of the wound site.

Optimum characteristics for an exit-site dressing

Ideal characteristics for an IV exit-site dressing include sterility, secure fixation, prevention of moisture accumulation, ability to visualise the exit site, ease of use and cost-effectiveness.

Sterility

Sterile dressings must be used, as it is possible for organisms found at the site to migrate down the catheter. Dressings should provide protection from extrinsic contamination.

Fixation and ease of use

The catheter must be securely fixed. Mobility at the site may encourage the migration of organisms along the catheter surface. Transparent polyurethane dressings have been found to be easy to apply and remove, and conform well to the skin for patient comfort (Wille et al, 1993). It will occasionally be necessary to secure a catheter to the skin with a secondary dressing. Polyurethane dressings allow patients to bathe or shower without the dressing becoming permeable to organisms.

Prevention of moisture accumulation

Gauze dressings will prevent the pooling of moisture but must be regularly examined for contamination as they will allow the passage of organisms when wet. Some polyurethane dressings are designed to promote a moist wound healing environment and have been adapted for catheter fixation. Although many of these types of dressing appear similar, factors such as the moisture vapour transmission rate can differ widely. Differences in pooling of moisture have been noted in randomised studies of these types of dressing (Keenlyside, 1991).

Cost-effectiveness

Exit sites must be examined daily for signs of infection (Maki, 1991). Although dry gauze is undoubtedly a cheaper alternative compared with polyurethane dressings, the former must be changed daily in order to observe the insertion site. The resulting costs in terms of nursing time to perform the required aseptic techniques may thus mean that in the long term the more expensive dressing is, in fact, the more cost-effective choice.

Change of dressing

Guidelines indicate that a change of dressing is needed every 48 to 72 hours (Elliott, 1993). Transparent dressings allow the site to be observed and should be changed when damp, soiled or loosened or at least weekly (O’Grady, 2003). A gauze dressing may need to be changed daily because of the need to remove it to examine the site for signs of infection. Strict asepsis is necessary when replacing a dressing. Handwashing and the use of an alcohol rub to disinfect the hands before contact with any part of an IV system are mandatory.

Cleaning the site

It has been suggested (Maki et al, 1991) that the area around the exit site should be cleaned with an antiseptic such as chlorhexidine and then sprayed with a further antiseptic - such as povidone iodine - then be allowed to dry for a further two minutes. The site should always be dry when replacing the chosen dressing (Maki et al, 1991). Topical antibiotic agents should be avoided owing to the risk of promoting fungal infections and generating antibacterial resistance (Zakrzewska-Bode et al, 1995).

Conclusion

Although the IV device is an essential component of modern health care, it must never be forgotten that its presence will increase the risk of healthcare-associated infection to the recipient. Skin flora such as the staphylococci spp are the organisms most commonly associated with line-related bacteraemia and can have potentially fatal consequences for patients.

The simplest and most effective method of reducing the rate of IV device-related complications is to ensure that the line is not left in place for longer than is necessary. IV devices should not be left in situ once the reason for their use has ceased (Smith, 1996). The need for the continued presence of any device must be reviewed and documented daily in order to reduce the risk of complications.

 
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