A 58-year-old man with a history of chronic alcohol use presents to the ICU with a 3-day history of fever, productive cough, and dyspnea. He was admitted 5 days ago with aspiration pneumonia and has been on mechanical ventilation for 2 days. On examination, he is febrile (38.9°C), tachypneic (RR 28/min), and hypoxic (SpO₂ 88% on FiO₂ 0.6). Chest X-ray shows bilateral infiltrates. Arterial blood gas reveals PaO₂ 65 mmHg, PaCO₂ 48 mmHg, pH 7.32. Pulmonary artery catheter shows PAWP 16 mmHg. Which of the following ventilatory strategies is most appropriate for this patient?

Explanation

## Diagnosis: ARDS This patient meets the Berlin Definition criteria for ARDS: - **Timing:** Within 1 week of known insult (aspiration pneumonia) - **Imaging:** Bilateral opacities on chest X-ray - **Oxygenation:** PaO₂/FiO₂ ratio = 65/0.6 = 108 (moderate ARDS: 100–200) - **Pulmonary edema:** PAWP 16 mmHg (normal, excludes cardiogenic cause) ## Lung-Protective Ventilation Strategy **Key Point:** The ARDSNet trial (NEJM 2000) established that low tidal volume (6 mL/kg of predicted body weight) with moderate-to-high PEEP reduces mortality in ARDS by 22% compared to conventional ventilation (12 mL/kg). **High-Yield:** The PEEP/FiO₂ titration table from ARDSNet guides escalation: - Start with PEEP 5 cmH₂O and FiO₂ 0.3 - Increase PEEP in increments of 2–3 cmH₂O as needed to maintain oxygenation - This patient with moderate ARDS and PaO₂ 65 on FiO₂ 0.6 requires PEEP escalation to 12–15 cmH₂O **Clinical Pearl:** Lung-protective ventilation minimizes barotrauma, volutrauma, and biotrauma, reducing ventilator-induced lung injury (VILI). ## Why Option 0 is Correct | Parameter | Lung-Protective | Conventional (Wrong) | |-----------|-----------------|----------------------| | Tidal Volume | 6 mL/kg PBW | 10–12 mL/kg PBW | | PEEP Strategy | Moderate-to-high (12–15) | Minimal (5 cmH₂O) | | Plateau Pressure | Target < 30 cmH₂O | Often > 35 cmH₂O | | Mortality Benefit | Yes (22% reduction) | No | **Mnemonic:** **ARDSNet = A**irway **R**estrictive **D**ose **S**mall **Net** (small tidal volumes, high PEEP) [cite:Harrison 21e Ch 297] ## Additional Management 1. Prone positioning if P/F ratio < 100 (this patient at 108, consider if deteriorates) 2. Neuromuscular blockade if dyssynchrony present 3. Fluid management: Conservative fluid strategy (target CVP < 4 mmHg) reduces ventilator days 4. Treat underlying cause (antibiotics for aspiration pneumonia)