First Things First (assess & treat for the following)

• Does patient have any respiratory distress that requires immediate attention?
  • PaCO2 > 50 mmHg
  • pH < 7.2
  • PaO2 < 70 mmHg or O2 saturation < 90%
• Does patient have evidence of low BP: systolic < 90 mmHg and/or diastolic < 60 mmHg?
• Does patient have mental status changes?
• Does patient have evidence of renal dysfunction &/or decreased urine output?
• Is the CXR showing bilateral, multilobar or progression of pulmonary infiltrates?
• Is the patient immunocompromised?
  • If yes, refer to Infections in Immunocompromised Host. Mgt of infection in immunocompromised hosts is very specific and should mandate early consultation with other specialists.

Definitions

• Community-acquired pneumonia (CAP)
• Severe community-acquired pneumonia (SCAP)
• Nosocomial pneumonia (NP) or hospital-acquired pneumonia (HAP)
• Ventilator-associated pneumonia (VAP)
  • Nosocomial pneumonia in a mechanically ventilated patient
• Healthcare-associated pneumonia (HCAP)
  • A NP in patients from nursing homes, dialysis centers, etc. who are exposed to multidrug-resistant (MDR) bacteria
• Important to differentiate the different groups of patients who may present with pneumonia in the ICU:
  • Patient origin: from the community, immunocompromised host either from the community or a nursing home, or currently in the hospital
  • Patient in the hospital and/or ICU who develops a pneumonia, and/or receiving mechanical ventilation, who develops a nosocomial pneumonia
• Demographic characteristics
  • Most relevant are age, comorbid conditions, medication use, history of immunosuppression, geographic & travel history, exposure to animals.
• SCAP
  • American Thoracic Society (ATS) defines SCAP & need for ICU admission by of at least 2 of the minor criteria parameters (systolic BP 90 mmHg or less, multilobar disease, PaO2/FIO2 < 250 torr) or one of the major criteria (need for mechanical ventilation or septic shock).
  • Mortality due to SCAP: 35-40%
    • NP (HAP, VAP, HCAP)
  • Mortality rate of NP in the ICU is 35-70%.
  • Risk factors for NP are grouped into 3 categories:
  • • Underlying acute illness that predisposes to secondary pneumonia
      • Acute lung injury
      • Abdominal, thoracic or cardiac surgery
      • Head injury/coma
      • Immunosuppressive illness
    • Coexisting medical illness
      • Age >60 yo
      • Obesity
      • Cardiac diseases
      • Albumin < 2.2 g/dl
      • Burns
      • Multiple organ failure
      • Chronic pulmonary diseases (chronic obstructive pulmonary disease, asthma, bronchiectasis, etc.)
      • Renal failure
      • Malignancies
      • Diabetes mellitus
      • Splenic dysfunction
    • Factors associated with therapies frequently used in ICU
      • Intubation with mechanical ventilation >2 days: most important, risk factor increases the risk 7- to 21-fold!
      • Antibiotic therapy
      • Bacteriologically virulent pathogens (Pseudomonas aeruginosa, Acinetobacter spp.)
      • Tracheostomy
      • Nasogastric tube use
      • Transfusion >4 units PRBC
      • Use of corticosteroids, immunosuppressants, H2 antagonists
      • Prolonged sedation and/or paralysis
      • Head of bed elevation < 30 degrees

Etiology

• SCAP
  • Patients with severe pneumonia in the ICU may have a pneumonia acquired:
    • In the community (SCAP),
    • In the hospital (HAP),
    • While being mechanically ventilated (VAP) or
    • From nursing homes, dialysis centers, etc. who are exposed to MDR bacteria (HCAP)
  • Most common cause of CAP is S. pneumoniae. 40% of S. pneumoniae is resistant to penicillin and is called drug-resistant S. pneumoniae.
  • S. pneumoniae, H. influenzae, Mycoplasma pneumoniae, influenza A virus, coronavirus (SARS), S. aureus, C. pneumoniae, C. psittaci, L. pneumophila, C. burnetii, gram-negative bacilli (Klebsiella spp, E. coli, Pseudomonas aeruginosa, etc). P. aeruginosa infection is a risk factor in patients with underlying lung diseases, as seen in bronchiectasis, cystic fibrosis & chronic corticosteroid use.
  • Opportunistic pathogens: P. carinii, cytomegalovirus, Cryptococcus neoformans, M. tuberculosis, M. avium intracellulare, A. israelii, N. asteroides, Aspergillus spp.
  • Rare pathogens: pertussis, typhoid, paratyphoid, brucellosis, leptospirosis, tularemia, anthrax, plague, Q fever
  • Viruses: Epstein-Barr virus, cytomegalovirus, measles, varicella, herpes, hantavirus
• NP (HAP, HCAP, VAP)
  • In the first 5 days of hospitalization, pneumonia is usually caused by Streptococcus pneumoniae, Haemophilus influenzae, anaerobic bacteria & less frequently Staphylococcus aureus (SA) (including methicillin-resistant SA [MRSA]) & Moraxella catarrhalis.
  • >5 days after admission, pneumonia is more commonly caused by hospital-acquired pathogens such as aerobic gram-negative bacilli, SA (often MRSA), Legionella pneumophila. Less frequent: influenza A & B, respiratory syncytial virus, Aspergillus spp., Pneumocystis carinii, Mycobacterium tuberculosis.
    • Gram-negative rods: Pseudomonas aeruginosa, Enterobacter spp., Acinetobacter spp., & enteric gram-negative rods (Klebsiella, E. coli, Proteus, Serratia) are the predominant pathogens & are at high risk to be drug-resistant.
    • SA (20-30% are MRSA). MRSA is seen in patients with underlying COPD or prior antibiotic use and/or in patients receiving mechanical ventilation.
  • Polymicrobial infections (60%) are common in patients on mechanical ventilation. MRSA, S. pneumoniae & H. influenzae are found in early-onset (before day 5) nosocomial pneumonia.