Page 855 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

586 PART 5: Infectious Disorders

MSSA Pseudomonas
6% 10%
Acinetobacter
Culture 4%
negative
20%
Empirical therapy
56% MRSA
Specific TX
14% 19%

Other + Enterobacteria a
3% 14%

No MDR risk
10%
FIGURE 65-3. Etiologic categories of ICU pneumonia cases. VAP are approximately one-third of patients. (Data from Kett D, Cano E, Quartin A, et al. Implementation of guidelines for
management of possible multidrug-resistant pneumonia in intensive care: an observational, multicentre cohort study. Lancet Infect Dis. March 2011;11(3):181-189.) Enterobacteriaceae—
a
specifically Klebsiella sp, Enterobacter sp, and E coli.

categories. Therefore, the majority appeared to have nosocomial patho- The backbone of empirical antibiotic therapy is a β-lactam antibiotic.
gens, most with risk factors for antibiotic resistance. A trend in many The only other potential class, fluoroquinolones, is no longer appropriate
studies toward lower percentages of nonfermentative gram-negative as monotherapy for MDR pathogens, given the rapid development of resis-
pathogens (eg, Pseudomonas and Acinetobacter) in HAP than in VAP tance and high percentage of resistant isolates. The emergence of strains
does not exclude them from the differential. with newer resistance mechanisms, including the Klebsiella pneumoniae
Knowledge of the etiology is still insufficient for appropriate carbapenemase (KPC), are generating pressure for the use of empirical
antibiotic treatment. HAP is as likely as VAP to have multidrug- colistin as the backbone of empirical therapy in some institutions.
resistant pathogens, especially Enterobacteriaceae. Specifically, some The major issue in empirical β-lactam treatment is which class—
of the recently described carbapenemases and extended spectrum piperacillin/tazobactam, late generation cephalosporins, or carbapenems—
β-lactamases (ESBLs) are just as likely as in HAP and HCAP. HAP is most efficacious. Avoiding the class of β-lactams used recently during
that requires transfer to the ICU is more likely to be caused by these the current hospitalization is probably the most reliable distinguishing
MDR pathogens than HAP successfully treated on the floor because criterion. Previously, a carbapenem was the most reliable choice in a patient
of the adverse consequences of inappropriate empirical treatment of previously exposed to extended spectrum penicillins and late-generation
MDR pathogens. cephalosporins. The appearance of various carbapenemases may make this
■ ANTIBIOTIC THERAPY assumption less reliable in the future.
More controversial is the need for combination therapy for gram-
Empirical Treatment: Table 65-8 represents the latest American negative pathogens. The need for combination therapy is predicated
Thoracic Society/Infectious Diseases Society of America (ATS/IDSA) on an assumption of P aeruginosa as a potential pathogen. Support for
combination therapy for Pseudomonas comes from retrospective analyses
guidelines recommended treatment for hospital-acquired pneumonia
94
in patients with risk factors for MDR pathogens. Unfortunately, the and older bacteremia data. Even less evidence exists for the benefit of
combination therapy for other pathogens. Proponents of combination
overwhelming majority of patients with HAP, especially those trans-
ferred to the ICU, have risk factors for MDR pathogens. Therefore, therapy point to the high percentage of inadequate empiric therapy with
107
any single agent, the increasing frequency of ESBLs and carbapenemases,
the algorithm for narrower spectrum monotherapy can only rarely be
used with confidence. and the association of inadequate empiric therapy with excess mortality.
Opponents emphasize the lack of supportive evidence from randomized
controlled trials, excess cost, and risk of morbidity and side effects, partic-
TABLE 65-8 Recommended Empirical Antibiotic Therapy in HAP Patients With ularly since aminoglycosides are the most common combination therapy
Risk Factors for MDR Pathogens used. No consistent improvement in outcome has been demonstrated
Suspected Pathogens Recommended Antibiotics with combination therapy despite the fairly consistent reduction in the
percentage of patients receiving inappropriate initial empirical therapy.
Non-MDR pathogens plus The need for MRSA coverage in all cases is also not clear. Detection of
Pseudomonas aeruginosa Piperacillin/tazobactam or MRSA nasal carriage has not consistently increased the probability that
Resistant Enterobacteriaceae, including ESBLs anti-pseudomonal cephalosporin or pneumonia in a colonized patient is due to MRSA.
a
Acinetobacter species a carbapenem PLUS anti-pseudomonal A critical component to empirical treatment of HAP is de-escalation
fluoroquinolone or aminoglycoside
of antibiotics once culture data are available. This emphasizes the need
94
Methicillin-resistant S aureus (MRSA) Linezolid or vancomycin to obtain a respiratory specimen for culture. This is easily accom-
plished in an intubated patient, which includes most HAP patients
Legionella pneumophila b Azithromycin or fluoroquinolone
admitted to the ICU. Good evidence supports the concept that if an
a For these two species, a carbapenem may be more reliable. adequate culture is negative for MRSA, Pseudomonas, Acinetobacter, and
b Use of fluoroquinolone for combination therapy above will cover. other highly resistant pathogens, then infection with these pathogens is
Adapted with permission from Guidelines for the management of adults with hospital-acquired, highly unlikely. The controversial combination therapy with aminogly-
ventilator-associated, and healthcare-associated pneumonia. Am J Respir Crit Care Med. February 15, cosides and empirical anti-MRSA coverage should then be discontinued.
2005;171(4):388-416. Certain aspects of this document may be out of date and caution should be used Lack of de-escalation may be associated with excess mortality if the ATS/
when applying the information in clinical practice and other usages. IDSA guidelines are used for HAP in the ICU. 107

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