Chapter 26 ICU Infections

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SECTION II • Medical and Surgical Crises

profoundly influence the likely site of infection and the organisms most commonly responsible. The selection of antimicrobials must take allergies and organ dysfunctions into account. Furthermore, individual hospitals have different spectra of bacte- ria causing a particular clinical syndrome, and even within a single hospital antibiotic susceptibility can vary widely among units. Therefore, practitioners must have a thorough knowledge of the patient being treated, the likely pathogens, and the anti- microbial susceptibility pattern of the hospital in which they practice. Antimicrobial options are constantly evolving. In recent years, for example, entirely new anti- biotic categories have been exploited and better tolerated formulations of long-established drugs have been commercially released. In the former category are drugs directed at organisms resistant to most standard agents, such as linezolid, dapto- mycin, and quinupristin–dalfopristin for meth- icillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus . Others include nontraditional antifungal agents, such as caspofungin for invasive Aspergillus and Candida infections. Nephrotoxicity of traditional amphoteri- cin desoxycholate has been attenuated by its lipid complex, cholesteryl sulfate complex, and lipo- somal variants. Voriconazole, a modified triazole, now offers a well-tolerated alternative to ampho- tericin that can be given orally as well as parenter- ally in the treatment of aspergillosis. Modifications within well-established antimicrobial categories have extended their spectra and/or limited their side effects. For example, fluoroquinolones (e.g., levofloxacin, gatifloxacin, and moxifloxacin) offer potent competition to traditional drugs in the treat- ment of typical and atypical pneumonia. Allergic sensitivity, renal insufficiency, hepatic dysfunction, bleeding tendency, or other vital organ dysfunctions may restrict options, but almost always, there exist more than one potentially effective antimicrobial combination. Suggestions that follow for antibiotic therapy are based on the most common pathogens and their usual susceptibility patterns while consid- ering the frequency and severity of side effects and ease and cost of administration. “Broad-spectrum” effectiveness is both a luxury and a liability, as the desire to cover a large number of potential patho- gens comes at a high price. Indiscriminate use of broad-spectrum antibiotics is rapidly producing multidrug-resistant bacteria. MRSA and penicillin- resistant Pneumococcus are now pandemic. New

and menacing pathogens such as multiresistant Enterococcus and Acinetobacter are recognized with increasing frequency. Unless patterns of antibiotic use change, it is likely such infections will grow in importance. Antibiotics are the only class of drugs that, when misused, can injure not only the patient being treated but nearby patients and those admit- ted to the ICU in the future. For example, the rou- tine use of vancomycin to treat diarrhea or to cover for Gram-positive pathogens may inadvertently “select out” organisms resistant to this useful drug. These highly resistant organisms then lurk in the ICU, ready to infect subsequent patients. The urinary tract, the most common site of ICU infection, accounts for almost 40% of all infec- tions. Although UTIs usually are inconsequential, the mortality rate for a bacteremic UTI approaches 30%. Risk factors for UTI include presence of a urinary catheter, female gender, diabetes, and advanced age. Colonization of urinary catheters occurs at a rate of about 5% to 10% per day, and most ICU-acquired UTIs occur in such colonized patients. Presumably, the colonized catheter per- mits retrograde passage of pathogenic bacteria into the bladder where they proliferate. Urinary catheter composition (Teflon rather than rubber) may reduce the infective hazard; however, there is no evidence that routine changing of the catheter or external application of antibiotic ointment decreases risk. Keys to preventing nosocomial UTI are sterile cath- eter insertion, early catheter removal, and mainte- nance of a closed drainage system. Diagnosis The diagnosis of UTI is all but certain when greater than 10 5 bacteria/mL are isolated from culture of freshly collected urine. This level of bacteriuria correlates well with the presence of more than one organism per high-power field of unspun urine. Unfortunately, fewer bacteria do not exclude the presence of infection. True infections have been documented with colony counts as low as 10 2 /mL. Escherichia coli, the most common bacterial isolate, occurs in about 30% of UTIs. Enterococcus and Pseudomonas are each recovered about 15% of the time in the ICU population. Klebsiella and Proteus species represent less common isolates. Contrary to previous teaching, in many cases, pure cultures Urinary Tract Infections Pathogenesis