Chapter 26 ICU Infections

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CHAPTER 26 • ICU Infections

of Staphylococcus epidermidis represent infection, not contamination. In the absence of frank pyuria or quantitative culture data, it is difficult to differ- entiate colonization from infection in critically ill patients with indwelling catheters. In the tenuous patient with bacteriuria, it is probably best to err on the side of brief, organism-directed antibiotic ther- apy. For more resilient patients in the ICU, treat- ment of asymptomatic bacteriuria may be deferred safely. Candida species are commonly recovered from urine. The choice of therapy for isolated candiduria should be based on a clinical judgment regarding whether the patient is “colonized” or “infected.” Unfortunately, few reliable signs distinguish these conditions. A clinical picture of sepsis, with recovery of Candida from blood cultures as well as urine, sug- gests disseminated infection that should be treated with intravenous antifungals such as amphotericin B, fluconazole, or caspofungin. Conversely, finding small numbers of yeast in an asymptomatic patient with an indwelling urinary catheter rarely requires systemic treatment (except expedited removal of the catheter). The most difficult situation occurs when large numbers of yeast or clumps of hyphal forms are found in the urine of an asymptomatic patient or a patient with only modest fever. Although sug- gestive of invasive infection, such patients usually respond promptly to fluconazole (oral or intrave- nous), especially if the urinary catheter can be removed. Without evidence of infection elsewhere, parenteral amphotericin B probably should be reserved for immunocompromised patients or those with limited physiologic reserves. Bladder irrigation with amphotericin B is time consuming, expensive, of uncertain benefit, and confounding to accurate assessment of urine output. Fluconazole has all but eliminated bladder irrigation. Pyocystis, an invasive infection of the bladder wall, may complicate oliguria or anuria, especially in patients requiring hemodialysis. In this setting, reduced urine flow allows bacteria to proliferate to massive numbers within the bladder. For oliguric patients with obscure fever, the bladder should be catheterized and the urine sediment examined. In the appropriate setting, murky, turbid, culture-posi- tive urine establishes the diagnosis. Treatment The aggressiveness of therapy should parallel the clinical severity of the acute syndrome and the underlying illness. As a rule, presumed UTIs should

be treated aggressively because patients in the ICU often have impaired immunity (diabetes, HIV infection, immunosuppressive therapy), numer- ous indwelling devices (e.g., vascular catheters, prosthetic heart valves, pacemakers), and marginal physiologic reserves. The treatment of UTI includes the promotion of urine flow and drainage, removal of urinary catheters (when feasible), and antibiotic therapy. Not all patients with bacteriuria require prolonged courses of expensive, broad-spectrum, intravenous antibiotics. Otherwise, stable immu- nocompetent patients can be treated successfully using enteral antibiotics (e.g., ampicillin, trime- thoprim–sulfamethoxazole, quinolones). Oral ther- apy is not appropriate for septic patients or patients with obstructive uropathy or a focal complication (e.g., renal abscess). The need for two drug cov- erage of pseudomonal infections in nonimmuno- compromised patients is uncertain, but two drugs effective against Pseudomonas should be given to patients with abnormal immunity. (These include intravenous aminoglycosides and antipseudomonal penicillins, fluoroquinolones, or third-generation cephalosporins.) If Enterococcus or Staphylococcus is deemed likely (based on the urine Gram stain or culture), vancomycin probably should be first-line therapy. Rarely, when the infection is life threaten- ing and the possibility of vancomycin resistance is high, linezolid is an appropriate choice. Urine con- centrations of renally excreted antibiotics often are dramatically higher than those used in sensitivity testing; therefore, UTIs often can be cured using an antibiotic to which the bacteria are found to be “resistant” in vitro . Because drainage bags provide important pathogen reservoirs, manipulations of the closed drainage system should be undertaken only when necessary and conducted with sterile tech- nique. Furthermore, drainage bags should not be raised above the level of the bladder, as often occurs during patient transport. Doing so, even briefly, pro- duces urinary stasis and promotes retrograde flow of potentially highly contaminated urine.

Pneumonia Pathogenesis

Pneumonia-producing organisms usually enter the lower respiratory tract in aspirated upper air- way secretions. Hematogenous seeding is a much less common mechanism. Unless the inoculum is very large, glottic closure, cough, and mucociliary clearance normally provide an effective mechanical