A 38-year-old woman with severe sepsis secondary to intra-abdominal infection develops ARDS on day 2 of ICU admission. She is on lung-protective ventilation (Vt 6 mL/kg IBW, PEEP 12 cm H₂O, FiO₂ 0.8). Current PaO₂/FiO₂ ratio is 95 mmHg. Plateau pressure is 28 cm H₂O. She is haemodynamically stable on low-dose noradrenaline. What is the most appropriate next step?

Explanation

## Clinical Assessment This patient has **severe ARDS** (PaO₂/FiO₂ = 95) despite optimal conventional ventilation. She meets criteria for prone positioning: - Moderate-to-severe ARDS (PaO₂/FiO₂ < 100) - Early intervention (day 2) - Haemodynamic stability - Plateau pressure within safe range (< 30 cm H₂O) **Key Point:** Prone positioning is a level-1 recommendation for moderate-to-severe ARDS when conventional management fails to achieve adequate oxygenation. The PROSEVA trial (2013) demonstrated 28-day mortality reduction with prone positioning in severe ARDS. **High-Yield:** Prone positioning mechanism: 1. Recruits dorsal (dependent) lung zones 2. Redistributes perfusion away from consolidated areas 3. Improves ventilation-perfusion matching 4. Reduces ventilator-induced lung injury 5. Requires 16+ hours daily for benefit **Clinical Pearl:** Prone positioning is safe if: - Plateau pressure < 30 cm H₂O (this patient: 28 cm H₂O ✓) - Haemodynamically stable (this patient: on low-dose vasopressor ✓) - No contraindications (recent abdominal surgery, spinal instability, etc.) ## Management Algorithm ```mermaid flowchart TD A[Severe ARDS<br/>PaO₂/FiO₂ < 100]:::outcome --> B{Lung-protective<br/>ventilation optimized?}:::decision B -->|No| C[Optimize PEEP, FiO₂,<br/>Vt 6-8 mL/kg]:::action B -->|Yes| D{Plateau pressure<br/>< 30 cm H₂O?}:::decision D -->|No| E[Reduce Vt or PEEP]:::action D -->|Yes| F{Haemodynamically<br/>stable?}:::decision F -->|No| G[Optimize fluids,<br/>vasopressors]:::action F -->|Yes| H[Initiate prone positioning<br/>16+ hrs/day]:::action H --> I{Oxygenation<br/>improved?}:::decision I -->|Yes| J[Continue prone positioning<br/>& lung-protective ventilation]:::action I -->|No| K{PaO₂/FiO₂ still < 80?}:::decision K -->|Yes| L[Consider ECMO]:::urgent K -->|No| J ``` **Citation:** [cite:Harrison 21e Ch 289]; Guérin et al., PROSEVA trial, NEJM 2013