A 52-year-old man with a history of type 2 diabetes mellitus is admitted to the ICU following aspiration of gastric contents during an emergency laparotomy for perforated peptic ulcer. On postoperative day 2, he develops acute dyspnea, tachypnea (RR 32/min), and hypoxemia (SpO₂ 88% on room air). Chest X-ray shows bilateral diffuse infiltrates. Arterial blood gas reveals PaO₂ 55 mmHg, PaCO₂ 32 mmHg on FiO₂ 0.6. Pulmonary artery wedge pressure (PAWP) is 14 mmHg. Which of the following is the most appropriate initial ventilatory strategy?

Question

Accepted Answer

B. Volume-controlled ventilation with tidal volume 6–8 mL/kg ideal body weight and PEEP titration. ## Diagnosis: ARDS (Acute Respiratory Distress Syndrome)

This patient meets the Berlin criteria for ARDS:
- Acute onset (postoperative day 2)
- Bilateral opacities on imaging
- Respiratory failure not fully explained by effusions, collapse, or nodules
- PaO₂/FiO₂ ratio = 55/0.6 = 92 (moderate ARDS: 100–200)
- Normal PAWP (14 mmHg) excludes cardiogenic pulmonary edema

## Lung-Protective Ventilation Strategy

**Key Point:** The ARDSNet trial (2000) established that low tidal volume (6–8 mL/kg ideal body weight) with appropriate PEEP reduces mortality in ARDS compared to conventional ventilation (12 mL/kg).

**High-Yield:** The ARDSNet protocol is the gold standard for ARDS ventilation:
- Tidal volume: 6–8 mL/kg predicted body weight
- Plateau pressure: target ≤30 cm H₂O
- PEEP/FiO₂ table: titrate PEEP based on oxygenation needs
- Mode: volume-controlled or pressure-controlled (both acceptable if tidal volume target met)

**Clinical Pearl:** Lung-protective ventilation reduces ventilator-induced lung injury (VILI) by preventing overdistension and repetitive alveolar collapse/re-expansion.

**Mnemonic: ARDS Vent Strategy = "6-8-30"**
- **6–8** mL/kg ideal body weight
- **30** cm H₂O plateau pressure limit
- **PEEP** titration per ARDSNet table

## Why This Patient Needs PEEP Titration

With PaO₂/FiO₂ = 92 (moderate ARDS), this patient requires:
- Initial PEEP 8–10 cm H₂O
- Incremental FiO₂/PEEP escalation per ARDSNet protocol
- Serial blood gas monitoring
- Plateau pressure checks to avoid over-distension

Answer

A. Pressure-controlled ventilation with tidal volume 12 mL/kg ideal body weight

Answer

C. Spontaneous breathing trial with minimal support to avoid ventilator-induced lung injury

Answer

D. High-frequency oscillatory ventilation as first-line therapy

Explanation

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