Chapter 26 ICU Infections

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SECTION II • Medical and Surgical Crises

the incidence can be reduced to a very low level. Despite better antibiotics, earlier recognition and improved understanding of the mechanisms of catheter-related infections, the case fatality rate for catheter-associated bacteremia remains significant. Mechanisms Three basic mechanisms can produce catheter- related infections (Fig. 26-4). (1) Most commonly, catheters are colonized at the skin–air interface, as bacteria migrate along their outer surfaces. Subcutaneous and eventual intravascular migration results in local infection or bacteremia if bacterial growth is uncontrolled by host defense or antibi- otic therapy. (2) Catheters also can become colo- nized by exposure to circulating microorganisms introduced into the circulation at a distant site. As foreign objects, standard catheters routinely form a “fibrin sheath” or biofilm. This microenviron- ment is a stagnant, fertile environment for patho- gen growth, helping sources of bacteria or fungi far distant from the catheter to seed these indwelling lines. Although antiadhesive treatments that mimic the cellular glycocalyx and impregnated biocidal coatings such as silver salts and chlorhexidine are helpful, they encumber added cost and a universally effective prophylactic approach is not yet at hand. (3) Only rarely, catheter-related infections are due to the infusion of a contaminated intravenous fluid or drug. Although, in theory, such infusate contami- nation can occur with any drug, the problem has been reported most often with parenteral nutrition

solutions and first-generation formulations of pro- pofol, an intravenous sedative/anesthetic with a

lipid vehicle. Risk Factors

Characteristics of patients at particular risk for catheter-related infection include diabetes mellitus, immunosuppressive therapy (especially neutrope- nia), immune deficiency diseases, skin diseases at the insertion site, and presence of sepsis at a dis- tinct source. Physician and environmental factors increasing the risk of intravascular catheter infec- tions include (1) catheter placement under emer- gency or nonsterile conditions, (2) insertion of multilumen catheters, (3) catheterization of a cen- tral vein, (4) prolonged catheterization at a single site, (5) placement by surgical cutdown, and (6) inexperience of the operator. Most catheter infec- tions can be prevented by using sterile technique when inserting, dressing, changing, and reconnect- ing catheters and by minimizing the frequency of catheter access. Rigorous sterility during insertion is essential; apart from sterile gloves, wide sterile barri- ers, surgical gowns, caps, and masks should be used for elective insertions. Chlorhexidine is superior to povidone-iodine solutions for skin preparation. Inexperience with catheter insertion increases infec- tion risk. (It is not clear whether catheters become contaminated during insertion or if less experienced operators are prone to produce more tissue trauma during the insertion process.) Multilumen catheters or catheters entered repeatedly (even for antibiotic

Intraluminal spread

Contaminated entry port

Hospital staff

Contaminated infusate

Extraluminal spread

Skin microflora

Dressing

Subcutaneous tissue

Hematogenous spread

Catheter tip contaminated on insertion through skin

FIGURE 26-4. Portals and pathways through which catheter-related infections can develop.