## Distinguishing ARDS from Cardiogenic Pulmonary Edema ### The Key Discriminator: Hemodynamic Profile **Key Point:** The pulmonary artery occlusion pressure (PAOP) is the single best discriminating feature between ARDS and cardiogenic pulmonary edema. ARDS is defined by a non-cardiogenic mechanism with PAOP ≤18 mmHg, whereas cardiogenic pulmonary edema has PAOP >18 mmHg. ### Comparison Table | Feature | ARDS | Cardiogenic Pulmonary Edema | |---------|------|----------------------------| | **PAOP (mmHg)** | ≤18 | >18 | | **Mechanism** | Increased capillary permeability | Elevated hydrostatic pressure | | **Bilateral infiltrates** | Yes | Yes | | **Acute onset** | Yes | Yes (usually) | | **Frothy sputum** | Uncommon | Common | | **PaO₂/FiO₂ ratio** | <300 | Variable | | **Protein content (edema fluid)** | High (>0.7) | Low (<0.7) | ### Why PAOP is the Gold Standard **High-Yield:** The Berlin Definition of ARDS (2012) explicitly requires PAOP ≤18 mmHg or absence of left atrial hypertension to exclude cardiogenic causes. This hemodynamic criterion is non-negotiable in ARDS diagnosis. **Clinical Pearl:** When PAOP cannot be measured directly (no pulmonary artery catheter), clinical judgment using echocardiography, BNP levels, and response to diuretics helps exclude cardiac etiology. However, the **measured PAOP ≤18 mmHg** remains the definitive discriminator. ### Why Other Features Are Not Discriminatory - **Bilateral opacities:** Both conditions present with bilateral infiltrates on imaging. - **Acute hypoxemia:** Both can present acutely with hypoxemia and low PaO₂/FiO₂ ratios. - **Frothy sputum:** While more common in cardiogenic edema, it is not a reliable discriminator and can occur in ARDS with severe capillary leak. [cite:Harrison 21e Ch 297]
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