Diagnosis of acute respiratory distress syndrome and differentiation from ventilator-associated pneumonia

Acute respiratory distress syndrome (ARDS) remains a significant cause of morbidity and mortality in surgical intensive care unit patients. A relatively predictable sequence of pathophysiologic events occur in the lung, which involve inflammatory mediators and neutrophils. The characteristic radiographic findings of ARDS may mimic ventilator-associated pneumonia (VAP), making the diagnosis of VAP difficult. The standard clinical criteria of fever, leukocytosis, purulent sputum, and infiltrate on chest radiograph are not specific for pneumonia in the surgical patient. The use of bronchoscopy with bronchoalveolar lavage and quantitative cultures can differentiate local and systemic inflammatory response to injury or blood loss from invasive bacterial pneumonia. Basing antibiotic therapy solely on the results of quantitative cultures is safe, because quantitative cultures identify VAP in less than half the patients with clinical evidence of pneumonia. Empiric therapy should be based on the microbiology of the intensive care unit rather than the results of the Gram stain.