Alameda County Medical Center / Highland General Hospital
Trauma Service

   ICU-Acquired Pneumonia
 
Risk Factors
The two most important risk factors for ICU-acquired pneumonia are the duration of mechanical ventilation and prior administration of broad spectrum antibiotics.  The other risk factors include age, coma, burn, trauma, acute lung injury (ARDS, pulmonary contusion), and severity of illness.  The risk of ICU-acquired pneumonia peaks around day 5 of mechanical ventilation.  After 15 days, the incidence plateaus and then declines, such that pneumonia rates are quite low in chronically ventilated patients.
 
Pathophysiology
The most common mechanism by which pneumonia occurs is aspiration of organisms from the upper respiratory or gastrointestinal tract.  Less common are direct inhalation and hematogenous spread.  Pneumonia can result when the inoculum is large, the microbes are virulent, or host defenses are impaired.  Organisms that are seen early (<72 hours) in a patient’s stay in the ICU vary markedly from those seen later.  “Early” organisms are largely S. aureus, S. pneumoniae, other Streptococci and H. influenzae, while “late” pathogens reflect resistant nosocomial pathogens, particularly Pseudomonas aeruginosa, MRSA, and Acinetobacter baumannii.
 
Diagnosis
The diagnosis of ICU-acquired pneumonia can be very difficult to establish.  Various combinations of clinical, radiographic, and laboratory criteria are frequently used to make the diagnosis.  These criteria include fevers, leukocytosis or leukopenia, purulent secretions, and the presence of a new and persistent radiographic infiltrate.  Quantitative cultures of tracheal aspirate, bronchoalveolar lavage, and protected specimen brush can aid in the diagnosis.  However, no combination of clinical diagnostic criteria has been identified to reliably diagnose pneumonia.
 
Prevention
 Treatment 
 
References
  1. Brown DL, Hungness ES, Campbell RS, et al.  Ventilator-Associated Pneumonia in the Surgical Intensive Care Unit.  JTrauma  2001, 51:1207-1216.
  2. Cardenas VJ.  Diagnosis and Management of Pneumonia in the Intensive Care Unit.  Chest Surg Clin N Am  2002, 12:379-395.
  3. Chaste J, Fagon JY.  Ventilator-Associated Pneumonia.  Am J Respir Crit Care Med  2002, 165:867-903.
  4. Hubmayr RD.  Statement of the 4th International Consensus Conference in Critical Care on ICU-Acquired Pneumonia – Chicago, Illinois, May 2002.  Intensive Care Med  2002, 28:1521-1536.

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