Distinguishing ARDS from Bilateral Pneumonia

Radiographic Features

The American Thoracic Society recommends that bilateral, diffuse ground-glass opacities that are typically peripheral and interstitial in distribution, often appearing more homogeneous across lung fields, are characteristic of ARDS 1
Dependent consolidation is common in ARDS, particularly in the posterior/basilar regions in supine patients, representing gravitational effects of increased pulmonary edema 2, 3
The absence of cardiomegaly or increased vascular pedicle width distinguishes ARDS from cardiogenic pulmonary edema 1
The Society of Critical Care Medicine notes that air bronchograms may be present within areas of consolidation in ARDS 2
Patchy, multifocal consolidations that are often asymmetric and may have a lobar or segmental distribution are characteristic of bilateral pneumonia 4

The American College of Chest Physicians recommends that acute onset (within 1 week of known clinical insult) with rapidly progressive hypoxemia is a key feature of ARDS 2, 3
A PaO2/FiO2 ratio ≤300 mmHg with PEEP ≥5 cm H2O defines the severity spectrum of ARDS 1
Bilateral infiltrates not fully explained by cardiac failure or fluid overload are a key feature of ARDS 1
Fever, purulent sputum production, and leukocytosis are more prominent in bilateral pneumonia 4, 6

The Infectious Diseases Society of America recommends that for all patients with suspected pneumonia or ARDS with clinical deterioration, obtain lower respiratory tract cultures (tracheal aspirate or BAL) BEFORE changing antibiotics 4, 6
Positive cultures with organisms ≥10³ cfu/ml (PSB) or ≥10⁴ cfu/ml (BAL) support pneumonia diagnosis 4
The American Thoracic Society notes that sterile cultures in absence of recent antibiotic changes argue against bacterial pneumonia 4

High-resolution CT scanning is superior to chest radiography for characterizing lung pathology and can help differentiate ARDS from pneumonia 7, 8
The Society of Critical Care Medicine recommends that ARDS on CT is characterized by bilateral ground-glass opacities with dependent consolidation, often with traction bronchiectasis in organizing phase 2, 3
Pneumonia on CT is characterized by more focal consolidations with possible cavitation, air bronchograms, or pleural involvement 5