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Calculate ARDS severity using the Berlin Definition criteria. Acute Respiratory Distress Syndrome (ARDS) is classified as mild, moderate, or severe based on the P/F ratio with specific PEEP requirements.
Clinical Use Only
This calculator is intended for healthcare professionals. ARDS diagnosis requires clinical correlation with imaging, timing, and exclusion of cardiac causes. Always consult critical care specialists for management.
| Severity | P/F Ratio | PEEP | Mortality |
|---|---|---|---|
| Mild | 201-300 mmHg | ≥ 5 cm H₂O | ~27% |
| Moderate | 101-200 mmHg | ≥ 5 cm H₂O | ~32% |
| Severe | ≤ 100 mmHg | ≥ 5 cm H₂O | ~45% |
The Berlin Definition (2012) eliminated the term "Acute Lung Injury (ALI)" and created three ARDS severity categories instead of two. It requires minimum PEEP of 5 cm H₂O for P/F ratio calculation, removed the pulmonary artery wedge pressure criterion, and added timing and risk factor requirements. This improves prognostic accuracy and standardizes diagnosis.
The PEEP requirement standardizes P/F ratio measurements across patients. ARDS involves alveolar collapse, and PEEP helps recruit collapsed alveoli. Measuring P/F ratio with adequate PEEP ensures the assessment reflects true lung injury severity rather than just degree of alveolar recruitment. Without minimum PEEP, P/F ratios would not be comparable.
Yes, the SF ratio (SpO₂/FiO₂) can be used when ABG is unavailable. SF ratio ≤ 235 roughly corresponds to P/F ≤ 200, and SF ≤ 315 corresponds to P/F ≤ 300. However, ABG is preferred for accurate classification and also provides information about ventilation (PaCO₂) and acid-base status.
The PROSEVA trial showed mortality benefit with prone positioning in severe ARDS (P/F < 150) when used early (within 36 hours) for prolonged sessions (≥16 hours/day). Prone positioning improves oxygenation by redistributing ventilation to dorsal lung regions and reducing ventilator-induced lung injury. Consider in all severe ARDS patients without contraindications.
The ACURASYS trial showed benefit with 48 hours of neuromuscular blockade in severe ARDS. However, the more recent ROSE trial did not show benefit with lighter sedation strategies. Current practice: consider neuromuscular blockade in severe ARDS with patient-ventilator dyssynchrony, but not routinely for all severe ARDS patients. Use shortest duration possible.
Key distinguishing features: ARDS requires known risk factor and acute onset, bilateral infiltrates are typically more peripheral, and cardiac function is normal/hyperdynamic. Cardiogenic edema has cardiac dysfunction (low EF, elevated BNP/troponin), central/perihilar infiltrates, and responds to diuresis. Bedside echocardiography is crucial when diagnosis uncertain.
Evidence is mixed. Low-dose methylprednisolone (1-2 mg/kg/day) may benefit persistent ARDS (after 7 days) and COVID-19 ARDS (dexamethasone 6mg daily). Not recommended in early ARDS (<14 days) or high-dose therapy. Consider in unresolving ARDS, but weigh risks of immunosuppression, neuromyopathy, and hyperglycemia.
Consider ECMO for severe refractory hypoxemia (P/F < 80 despite optimization) or uncompensated hypercapnia with pH < 7.25 despite lung-protective ventilation. The EOLIA trial showed trend toward benefit. Transfer to ECMO-capable center should occur early, before patient develops multi-organ failure. Best outcomes when initiated within 7 days of mechanical ventilation.