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Controlling intravascular catheter infections |
Summary
Sepsis related to intravenous catheters is the commonest cause of bloodstream infections in Australia. The risk of infection is highest with percutaneous central venous catheters, somewhat lower with tunnelled or subcutaneous catheters, and lowest with peripheral intravenous catheters. The best prevention is removal of intravenous lines when they are no longer necessary. Optimal insertion techniques and line maintenance are also important. Once infection occurs, the line should generally be removed. Antibiotic therapy is directed against suspected micro-organisms (usually staphylococci) and modified with the results of cultures. If septic shock occurs general supportive measures including intravenous fluids, inotropic drugs and observation in an intensive care unit will also be necessary.
Key words: sepsis, bacteraemia, bloodstream.
(Aust Prescr 2003;26:41-3)
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Introduction
Intravenous catheters are indispensable in modern medicine and are no longer
restricted to hospital inpatients. There is a growing number of patients on
'home' intravenous therapy, predominantly for total parenteral nutrition or
cancer chemotherapy. However, these devices are increasingly associated with
sepsis and are now the commonest cause of all bloodstream infections. These
infections cause significant morbidity and mortality.
Rates of intravascular catheter-associated bloodstream infections
In Australia, there are at least 3500 cases of intravenous catheter-associated
bloodstream infections annually. These are associated with a case fatality
rate of 24%, and the mortality rate directly attributable to intravenous catheter
sepsis is 12%. This equates to 1.5 bloodstream infections per 1000 admissions.1
Percutaneous central venous catheters are associated with 23 bloodstream infections per 1000 catheters. In contrast, catheters in peripheral
veins are associated with only 0.36 bloodstream infections per 1000 catheters.2 Peripheral
vein catheters remain in situ an average of 1.5 days, while central venous
catheters remain in situ about four times longer (an average of 5.5 days).
The daily infection risk with central venous catheters is about 20 times that
of peripheral catheters. Tunnelled or surgically implanted catheters (Hickmans,
Portacath) and peripherally inserted central venous catheters appear to have
a quarter the daily risk of percutaneous central venous catheters, but they
still pose a much higher risk than peripheral catheters.
Why there is such a disproportionate infection rate of central venous catheters
is unclear. It may reflect the poorer health of patients requiring this type
of therapy as well as the longer duration of intravenous access in this group.
The infusion of total parenteral nutrition, the use of triple lumen (versus
single lumen) catheters, and some catheter insertion sites (jugular and femoral
sites in particular) are independent risk factors. However, all these factors
only partially account for the marked differences in daily infection risk rates.
Of concern, is the observation that a large number of intravenous catheters
(including central venous catheters) in hospitalised patients are not in active
use for prolonged periods of time but remain in situ 'just in case'. Also,
some catheters are being used for interventions that are not necessary (for
example, total parenteral nutrition when nasogastric feeding is possible).
Pathogenesis
There are several modes of colonisation with pathogens.3 At
the skin entry site, the outer surface of the catheter can become colonised
with organisms originating from the skin. These bacteria can then migrate proximally
along the catheter's surface to reach the bloodstream. Alternatively, the catheter's
inner surface may become colonised by introduction of organisms through the
catheter hub (e.g. from the hands of hospital staff). Rarely, micro-organisms
may be introduced by contaminated infusate (especially total parenteral nutrition).
The point at which colonisation changes to invasive infection is unclear, but
it is thought to be related to the number of organisms present on the catheter,
and is time dependent (infection is rare within the first 48 hours of catheter
placement).
The role of biofilms (collections of bacteria adherent to the catheter surface
and organised within an extensive glycocalyx) is important. Although micro-organisms
in biofilms are visible on microscopy, they are often unculturable, and are
protected from the effects of antibiotics. If biofilms are present, cure is
usually only possible by removing the catheter.
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Microbiology
Skin-associated micro-organisms are the predominant isolated pathogens (see
Table 1). Coagulase-negative staphylococci (e.g. Staphylococcus
epidermidis) are the commonest, possibly because they appear to have
the best adherence
to inert surfaces. Staphylococcus aureus infections
are second in frequency, with the infection risk being highest in patients
with neutrophil defects or
venous thrombophlebitis. Enteric mucosal micro-organisms such as enterococci,
Enterobacteriaceae, pseudomonas, and candida
species may colonise the catheter either by colonising the skin, by colonising
the infusate (especially total
parenteral nutrition) or by haematogenous seeding from mucosal breaches.
Diagnosis
In the majority of bloodstream infections associated with central venous catheters, there will be little or no evidence of sepsis at the insertion site (in contrast to infections associated with peripheral vein catheters).
The diagnosis of catheter-associated bloodstream infection requires a positive culture of blood from a peripheral vein and clear evidence implicating the catheter as the source. The culture of 15 or more colonies of a pathogen from a catheter tip is diagnostic of catheter-associated bloodstream infections. Unfortunately, this method only has a positive predictive value of 16-31% because most catheter tip cultures are negative.4
Another approach to diagnosis (which conserves the catheter) is simultaneous
culture of blood drawn peripherally and blood drawn from the catheter. As the
density of organisms is greatest in the catheter specimen (if it is the source
of sepsis), the catheter blood culture will usually become positive at least
two hours earlier than the peripheral blood culture (using the Bactec system).
This technique has been reported to have a sensitivity and specificity of greater
than 90% and a positive predictive value of approximately 80%.
Treatment
Catheter removal is usually essential in all cases of catheter-associated
bloodstream infections, with the exception being some cases associated with
Hickmans or Portacath catheters. Even with these, catheter removal is still
essential if Staphylococcus aureus or candidal septicaemia occurs and strongly
recommended if Gram negative bacilli (due to likelihood of treatment failure)
are isolated from blood cultures.
If low virulence organisms such as coagulase-negative staphylococci are isolated,
removal of the line itself may be sufficient to resolve the infection, but
usually the patient is also treated with one week of intravenous antibiotics.
If a Hickmans or Portacath is involved and is not removed, the patient is treated
with two weeks of intravenous antibiotics. This may control the infection in
80% of cases, however, if the bacteraemia or fever persist despite appropriate
antimicrobial therapy, the central venous catheter must be removed.
If bloodstream infection is suspected and the catheter is replaced, the new
central venous catheter should not be passed over a guide-wire at the same
venepuncture site. If it is, the new catheter will almost certainly be contaminated
with the same organism (see Table 2 for further prevention issues).
While awaiting blood culture results, empiric therapy to cover staphylococci
and Gram negative bacilli (i.e. vancomycin, or flucloxacillin in combination
with an aminoglycoside) is the best initial treatment. The regimen may be modified
once the pathogen is identified.
If Staphylococcus aureus is isolated, treat with antibiotics (e.g. flucloxacillin
if sensitive) for a minimum of 14 days after catheter removal (4-6 weeks therapy
if persistent fevers or a suspected distant focus of infection). If candida
is isolated, treatment is generally with a triazole (e.g. fluconazole) for
at least 14 days after the last positive blood culture. The fungal isolate
should be fully identified, as species other than Candida albicans are often
resistant to triazoles.
If the patient remains febrile after removal of the device, three sets of
blood cultures should be obtained. Endocarditis or septic thrombophlebitis
should be suspected if blood cultures remain positive for more than 48 hours
after the device has been removed.
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Conclusion
Catheter-related sepsis is a common complication of modern medical therapy.
Reduction of this complication may be achieved by minimising intravenous access.
If there is no absolute need for intravenous access, remove the intravenous
line. Use peripheral access rather than central venous catheters wherever possible.
When central venous catheter access is necessary, use peripherally inserted
venous catheters or tunnelled/implanted lines if possible. If bloodstream infections
occur, removal of the intravenous line is essential, with only a few exceptions
(Hickmans- or Portacath-associated bloodstream infections with low virulence
organisms such as coagulase-negative staphylococci).
References
1. Collignon PJ. Intravascular catheter associated sepsis: a common problem. Med J Aust 1994;161:374-8.
2. Managing bloodstream infections associated with intravascular catheters. Drug Ther Bull 2001;39:75-80.
3. Crump JA, Collignon PJ. Intravascular catheter-associated infections. Eur J Clin Microbiol Infect Dis 2000;19:1-8.
4. Maki DG, Weise CE, Sarafin HW. A semiquantitative culture
method for identifying intravenous-catheter-related infection. N Engl J Med
1977;296:1305-9.
Further reading
Raad I. Intravascular-catheter-related infections. Lancet 1998;351:893-8.
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