Published on 25/03/2015 by admin
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Chapter 172 Infection Associated with Medical Devices
Patricia M. Flynn
Despite the therapeutic successes and convenience of the many synthetic devices used in pediatric patients, infectious complications are problematic. The pathogenesis of device-related infection is not completely defined, but many factors are important, including the susceptibility of the host, the composition of the device, the ability of microorganisms to adhere to the device itself or to the biofilm that quickly forms on it, and environmental factors that include the insertion technique and maintenance of the device.
Intravascular access devices range from short stainless steel needles to multilumen implantable synthetic plastic catheters that are expected to remain in use for years. Infectious complications include localized infections and catheter-related bloodstream infections (CRBSI). Exit site infection denotes infection localized to the exit site often with purulent discharge. Tunnel tract infection indicates infection in the subcutaneous tissues tracking along the catheter, which may also include serous or serosanguineous discharge from a draining sinus along the catheter path and usually mandates removal of the catheter. Pocket infection indicates suppurative infection of a subcutaneous pocket containing a reservoir, usually of a totally implanted device. The source of catheter infection is usually contamination by bacteria on the skin rather than bacteremia from another focus seeding the intravascular device. Infection with the microbial skin flora at the insertion site may extend along the external surface of the catheter. This route of infection is most common in intravascular catheters in place for <30 days. Organisms may also gain access to the intraluminal portion of the catheter through improper handling of the catheter hub or contaminated infusate. This route of infection is thought to be more prevalent in catheters in place for >30 days. Gram-positive cocci predominate in both categories, with more than half caused by coagulase-negative staphylococci. Gram-negative enteric bacteria are isolated in approximately 20-30% of episodes, and fungi account for 5-10%.
The clinical manifestations of local infection include erythema, tenderness, and purulent discharge at the exit site or along the subcutaneous tunnel tract of the catheter. CRBSI may occur with or without local infection. Additional clinical findings include fever without an identifiable focus and rigors associated with catheter use.
The diagnosis of localized infection is established clinically. A Gram stain and culture of exit site drainage should be performed and may help elucidate the microbiologic cause. The diagnosis of CRBSI is confirmed by performing quantitative blood cultures simultaneously from the catheter and the peripheral vein. CRBSI is diagnosed when at least a 3-fold higher number of organisms are isolated from blood obtained via the catheter as compared to blood obtained via a peripheral vein. If quantitative blood cultures are not available, a catheter blood culture that becomes positive >2 hr before a peripheral culture, with equal amounts of blood using a radiometric detection system, may also be used for diagnosis. CRBSI can also be diagnosed by isolation of the same organism from the blood and the catheter tip. However, this method requires catheter removal and is not optimal for patients with long-term devices.
Short-term peripheral catheters are most commonly used in pediatric patients, and infectious complications occur infrequently. The rate of peripheral CRBSI is <0.15%. Patient age <1 yr, duration of use for >144 hr, and some infusates (e.g., total parenteral nutrition, lipids) are associated with increased risk for catheter-related infection.
Central venous catheters (CVCs) are widely used in both adult and pediatric patients and are responsible for the majority of catheter-related infections. They are commonly used in critically ill patients, including neonates, who often have many risk factors for the development of nosocomial infection. Patients who are in an intensive care unit and who have a CVC in place have a 5-fold greater risk for developing a nosocomial bloodstream infection than those without a CVC. The means for optimal maintenance of these catheters remains controversial. Although prevalence of infection increases with prolonged duration of catheter use, routine replacement of a CVC, either at a new site or over a guide wire, results in significant morbidity and should not be adopted. Catheters should be removed when they are no longer needed. The use of peripherally inserted central catheters (PICCs), which are inserted into a peripheral vein with the distal end in a central vein, has increased in pediatric patients. Published experience with these devices in children is scanty, but studies in adults document a life span of approximately 3 mo and infection rates of 1.9 episodes/1,000 catheter-days, significantly lower than for CVCs.
When prolonged intravenous access is required, a cuffed silicone rubber (Silastic) catheter may be inserted into the right atrium through the subclavian, cephalic, or jugular vein. The extravascular segment of the catheter passes through a subcutaneous tunnel before exiting the skin, usually on the superior aspect of the chest (Broviac or Hickman catheters). Totally implanted devices consist of a reservoir or port placed in a subcutaneous pocket with a self-sealing silicone septum at the distal end that permits repeated percutaneous needle insertions for administration of drugs. The use of central venous devices has improved the quality of life of high-risk patients but has also increased the risk for various infections. The incidence of local (exit site, tunnel, and pocket) infection is 0.2-2.8/1,000 catheter-days. The incidence of Broviac or Hickman CRBSI is 0.5-6.8/1,000 catheter days, whereas that for implantable devices is 0.3-1.8/1,000 catheter-days. The risk for catheter infection is increased among premature infants, young children, and those receiving total parenteral nutrition.
If either localized infection or CRBSI is diagnosed in a short-term peripheral catheter or CVC, the device should be removed. Antibiotics should be administered in cases of systemic infection, with the exception of uncomplicated coagulase-negative staphylococcal bacteremia in normal hosts, for which catheter removal is sufficient.
For infections associated with long-term vascular access devices (Hickman, Broviac, totally implantable devices), antibiotic treatment is successful for most systemic bacterial infections without removal of the device. Antibiotic therapy should be directed to the isolated pathogen and given for a total of 7-14 days, depending on the organisms isolated. CRBSI caused by Staphylococcus aureus may require a longer duration of therapy. Until identification and susceptibility testing are available, empirical therapy, based on local antimicrobial susceptibility data and usually including a 3rd or 4th generation cephalosporin or aminoglycoside plus vancomycin is indicated. Antibiotic lock or dwell therapy,
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