Managing Community Acquired Pneumonia in the ICU

Patient SK presented with increasing
shortness of breath, right-sided chest pain, productive cough in a change in level of
consciousness — she was febrile with an O2 sat of
eighty-three percent on room air; she had an elevated white blood cell count
and on chest x-ray there was a consolidation. SK was intubated and transferred to
the ICU. Blood cultures were sent and antibiotics
were administered. She is diagnosed with Community-acquired
pneumonia or CAP. In Canada, pneumonia (including influenza) is the eighth most common cause of death. A third of patients with CAP are admitted
to the ICU where mortality rates range from 20 to
50 percent. Like all ammonia syndromes the diagnosis
is based on the appropriate constellation of clinical signs and symptoms. Blood and sputum cultures should be sent for any
patient with CAP sick enough to be admitted to the
hospital, especially the ICU, but they are often negative. Therefore, antimicrobial therapy is often
empiric for the entire course of treatment. It is important to target therapy to
most likely pathogens, current resistance rates and where possible, known, recent, antibiotic use. The key pathogens to consider in CAP
include Streptococcus pneumoniae, and Haemophilus influenza – and in the ICU Legionella species. Staph. aureus or or methicillin-resistant
Staph. aureus (MRSA) should be considered in a
patient with known colonization or risk factors. During flu season, influenza A & B are notable causes of pneumonia. Surveillance systems routinely monitor
resistance in Strep pneumo and H. flu. Current macrolide resistance in Strep pneumo
is around 30 percent while penicillin and cephalosporin
resistance is less than one percent and fluoroquinolone resistance is
between one to two percent. Outpatient rates of ampicillin resistance in H. flu are roughly 18 percent. Therefore for SK a reasonable choice
would be a third-generation cephalosporin such as ceftriaxone or cefotaxime, plus a macrolide — like azithromycin. The third-generation cephalosporin will
cover Strep pneumo, H. flu, and gram-negatives like E coli or Klebsiella pneumoniae. The macrolide will cover Legionella.
During flu season, consider adding oseltamivir. Guidelines recommend either a macrolide
or a fluoroquinolone for severe CAP. Using a macrolide where possible will avoid the overuse of quinolones (which are a risk factor for the NAP1 strain of C. dificile.) If a bug is identified — tailor the
antibiotics to target it. Regardless, seven days of therapy for
patients with CAP, even those in the ICU is sufficient — unless there are
complications like Legionella, or Staph. aureus bacteremia. Key messages: target the most likely pathogens, for
most patients choose a third-generation cephalosporin
plus a macrolide; and treat for seven days.

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