A 52-year-old man with community-acquired pneumonia is admitted to the ICU. On day 3, he develops acute hypoxemic respiratory failure with bilateral infiltrates on chest X-ray and PaO₂/FiO₂ ratio of 180 mmHg. He meets diagnostic criteria for ARDS. Regarding the pathophysiology and management of ARDS, all of the following statements are correct EXCEPT:

Explanation

## Pathophysiology of ARDS **Key Point:** ARDS is characterized by increased alveolar-capillary permeability, leading to protein-rich edema fluid (edema fluid-to-plasma protein ratio >0.65), which distinguishes it from cardiogenic pulmonary edema. ## Ventilation Strategy in ARDS **High-Yield:** The ARDSNet trial (2000) demonstrated that **low tidal volume ventilation (6 mL/kg of ideal body weight)** reduces mortality by ~22% compared to conventional ventilation (12 mL/kg). High tidal volumes (10–15 mL/kg) are now contraindicated because they cause barotrauma and worsen ventilator-induced lung injury (VILI). **Clinical Pearl:** Lung-protective ventilation is the cornerstone of ARDS management and is supported by all major guidelines (ACCP, ARDS Definition Task Force). ## Evidence-Based Interventions in ARDS | Intervention | Evidence | Mortality Benefit | | --- | --- | --- | | Low tidal volume (6 mL/kg IBW) | ARDSNet RCT | Yes (~22% reduction) | | Prone positioning (16+ hrs/day) | PROSEVA trial | Yes in moderate-severe ARDS | | Neuromuscular blockade (early) | ACURASYS trial | Yes in severe ARDS | | High tidal volume (10–15 mL/kg) | ARDSNet | **Increased mortality** | | PEEP titration | ALVEOLI, LOV trials | Unclear benefit | **Warning:** High tidal volume ventilation increases plateau pressure, promotes alveolar overdistension, and worsens outcomes. This is the **incorrect statement** in the question. ## Correct Statements Explained 1. **Increased capillary permeability** — hallmark of ARDS; mediated by inflammatory cytokines (TNF-α, IL-1, IL-6), neutrophil infiltration, and endothelial injury [cite:Harrison 21e Ch 296]. 2. **Prone positioning** — PROSEVA trial (2013) showed 16 hours daily prone positioning in moderate-to-severe ARDS reduced 28-day mortality from 32.8% to 16.0% [cite:Harrison 21e Ch 296]. 4. **Neuromuscular blockade** — ACURASYS trial (2010) demonstrated early paralysis (first 48 hours) in severe ARDS reduced mortality and improved ventilator synchrony [cite:Harrison 21e Ch 296]. ## Summary **Mnemonic: ARDS Management — "LPPN"** - **L**ow tidal volume (6 mL/kg IBW) - **P**rone positioning (16+ hrs) - **P**ositive end-expiratory pressure (individualized) - **N**euromuscular blockade (early, severe cases)