Host factors

Infection control measures in ICUs are traditionally directed at limiting person-to-person spread of infection and spread from other exogenous sources. These measures often fail because they may have little effect on the endogenous flora, which is an important source of infection in critically ill patients. Monitoring of antibiotic use can control the selection of resistant and sometimes more virulent micro-organisms from a patient's endogenous flora. The emergence of resistant endogenous strains is a particular problem with Gram-negative bacilli (e.g. Pseudomonas and Enterobacter species).

The normal host defense mechanisms of critically ill patients are impaired by underlying diseases or as a result of medical interventions (e.g. intravascular catheters and endotracheal tubes). Routine replacement of central venous catheters is recommended to prevent infection based on the observation that the risk increases exponentially after 3 to 5 days of catheterization. However, the duration of placement is still under debate, as is the use of guidewire exchange. If semiquantitative tip cultures are positive, a new catheter must be inserted at a new puncture site. Strict aseptic techniques (with sterile gowns, mask, and gloves) for catheter insertion should be applied. Written policies concerning the use of invasive devices should be implemented, and catheter insertion techniques and care should be standardized.

The gut flora serve as a main reservoir for endogenous nosocomial infection. The normally low pH of the stomach is often neutralized by H 2 blockers or antacids, promoting overgrowth of enteric micro-organisms associated with nosocomial infections like ventilator-associated pneumonia. Admission surveillance cultures of the gastrointestinal tract to identify the 'carrier state' of patients colonized with endogenous flora have been suggested. This may help to prevent infection by stopping the pathway from colonization to infection. Selective decontamination of the digestive tract (SDD) using topical antimicrobials to prevent infections from emerging from the endogenous gut flora is controversial, and should not be used routinely in the ICU setting.

Gut translocation may occur in ischemic gut, in obstruction, or during periods of hypothermia. Thus maintenance of adequate perfusion may help to maintain intact barrier functions.

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