SKIN PREPARATION procedures may leave up to 20% of resident skin bacteria alive. During venipuncture, these pathogens can adhere to the catheter as it passes through the skin, setting the stage for a biofilm coating on the external catheter surface. Catheter movement also can let organisms into the bloodstream at venipuncture sites, leading to catheter-related bloodstream infections.
In this article, I'll describe the profile of microorganisms in wet, dry, and oily human skin, then discuss how these factors affect catheter-related infections and what you can do to minimize your patient's risk.
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Human skin falls into three types: wet, dry, and oily. Wet skin, such as that in the axilla and groin, is highest in number and types of microbes. Dry skin on the extremities has the fewest numbers and types of microbes. (This is one reason why the reported rate of catheter-related infection is lower in midline and peripherally inserted central catheters [PICCs] compared with central vascular devices.)
Oily skin is found on the forehead, neck, and upper chest. This skin type has more numbers and types of organisms than dry skin, but less than wet skin.
The amount of bacteria on the skin also varies with a patient's sex: Men have more skin flora with more cells per colony than do women. Age is another consideration: Age-related decreases in sweating and atrophy of sebaceous glands give an older person's skin more water content (even though it may appear dry). As a result, yeast is more easily cultured from the skin of older people than from that of young people.
Getting to the hub of the problem
Most microorganisms that cause catheter-related infections come from the patient's own skin or the catheter hub. When signs and symptoms of infection develop within the first week after catheter insertion, the skin is the likely source; infections occurring later are probably caused by microorganisms introduced via the catheter hub.
For years, clinicians believed that microbes migrate from the skin down the catheter surface, colonizing the catheter and causing bloodstream infection. But new research reveals a different scenario. Bacteria that attach to the catheter as it passes through the skin produce and encase themselves in biofilm-a self-protective polymeric matrix. Bloodstream infection occurs when biofilm breaks away and floats freely in the bloodstream. Biofilm may break away spontaneously as it grows or be dislodged by blood flow or catheter flushing.
Along with microbes introduced during catheter insertion, other microbes may be floating in the bloodstream or introduced via contaminated I.V. fluid. These microbes can also attach to the catheter surface and produce biofilm.
Always present on intravascular catheters, biofilm resists the immune system's defense mechanisms. Antibiotics, which can kill free-floating bacteria in the bloodstream, can't penetrate biofilm's deep layers.
Preventing infections
To reduce the risk of introducing microbes during catheter insertion and routine catheter care, use a 2% chlorhexidine-based preparation, the product most commonly recommended for skin antisepsis. Repeated use of chlorhexidine enhances its effectiveness because it binds with skin cells, which prolongs its microbicidal activity.
Maintain proper hand hygiene and use sterile technique and barrier protection (sterile gloves, gown, cap, mask, and large sheet drapes) when inserting midline catheters and PICCs. Use catheters with antimicrobial coatings for short-term therapy in adults. (Coated PICCs recently became available, but coated tunneled catheters and implanted ports aren't on the market yet.)
Because microorganisms (including those from your skin) can be introduced each time you manipulate the catheter hub, minimize the number of times you handle the hub. Perform meticulous hand hygiene and clean hub surfaces and injection ports before use.
By knowing more about how catheter-related infections occur, you can help implement methods to reduce your patient's risk.
Lynn C. Hadaway is president of Lynn Hadaway Associates, Inc., in Milner, Ga. This article was adapted from Skin flora and infection, Journal of Infusion Nursing, LC Hadaway, January/February 2003.
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