Regarding the diagnostic criteria, risk factors, and prognostic indicators in ARDS, all of the following are correct EXCEPT:

Explanation

## Berlin Definition of ARDS (2012) **Key Point:** The Berlin Definition is the current diagnostic standard and requires: 1. **Bilateral opacities** on chest X-ray or CT (not explained by pleural effusion, atelectasis, or nodules) 2. **Onset within 1 week** of known insult (clinical insult or new/worsening respiratory symptoms) 3. **Respiratory failure not fully explained** by cardiac failure or fluid overload 4. **PaO₂/FiO₂ ratio** on PEEP ≥5 cmH₂O: - Mild: 200–300 mmHg - Moderate: 100–200 mmHg - Severe: <100 mmHg [cite:JAMA 2012; Harrison 21e Ch 296] ## Exclusion of Cardiac Pulmonary Edema **High-Yield:** The Berlin Definition explicitly states that ARDS is a diagnosis of **exclusion** of cardiogenic pulmonary edema. However, **PAOP >18 mmHg does NOT automatically exclude ARDS**—both conditions can coexist (e.g., sepsis + heart failure, pneumonia + MI). The criterion is clinical judgment: if pulmonary edema is **fully explained by cardiac failure**, then it is not ARDS. If there is additional inflammatory lung injury despite elevated PAOP, ARDS may still be diagnosed. **Warning:** A common misconception is that PAOP >18 mmHg is an absolute exclusion criterion. In reality, ARDS can occur in patients with elevated PAOP if there is evidence of increased capillary permeability (high edema fluid-to-plasma protein ratio) and bilateral infiltrates not solely attributable to heart failure. ## Risk Factors for ARDS **Mnemonic: "ARDS Risk — SAPP"** - **S**epsis (most common, ~40–50% of cases) - **A**spiration (second most common, ~20–30%) - **P**neumonia (community-acquired or hospital-acquired) - **P**ancreatitis, Pulmonary contusion, Polytrauma Other risk factors: transfusion, transoesophageal echocardiography, fat embolism, near-drowning, amniotic fluid embolism. ## Prognostic Indicators | Factor | Prognostic Significance | | --- | --- | | **PaO₂/FiO₂ ratio** | Lower ratio = worse prognosis. Severe (<100) has ~40% mortality; mild (200–300) has ~25% mortality | | **Age** | Older age associated with higher mortality | | **SOFA score** | Higher SOFA = worse prognosis | | **Sepsis as cause** | Associated with higher mortality than other causes | | **Ventilator settings** | High plateau pressure, high PEEP requirement = worse prognosis | **Clinical Pearl:** A PaO₂/FiO₂ ratio >300 mmHg indicates milder lung injury and is associated with better outcomes and lower mortality compared to severe ARDS (ratio <100 mmHg, ~40% mortality). ## The Incorrect Statement **Option 4 is WRONG:** PAOP >18 mmHg does not exclude ARDS. The Berlin Definition requires that pulmonary edema not be **fully explained** by cardiac failure, but elevated PAOP alone does not rule out ARDS. Patients can have both elevated PAOP and ARDS (e.g., septic cardiomyopathy, pneumonia with concurrent heart failure).