What is the evidence behind proning in severe Acute Respiratory Distress Syndrome (ARDS)?

Evidence for Prone Positioning in Severe ARDS

Prone positioning should be implemented for patients with severe ARDS (PaO2/FiO2 ratio <100-150 mmHg) for at least 16 hours per day to significantly reduce mortality. 1, 2

Physiological Benefits of Prone Positioning

Prone positioning provides several physiological benefits in ARDS:

• Redistribution of lung densities with recruitment of well-perfused dorsal regions 1
• More homogeneous distribution of ventilation and improved ventilation/perfusion matching 1, 3
• Reduction in alveolar shunt and better gas exchange 1
• Decreased risk of ventilator-induced lung injury (VILI) through more even distribution of transpulmonary pressure 1, 3
• Reduced compression of lung segments by the heart 1
• Enhanced drainage of secretions 4

These mechanisms collectively lead to improved oxygenation, with studies showing a significant increase in PaO2/FiO2 ratio (mean difference of 23.5 mmHg) 5.

Clinical Evidence for Mortality Benefit

The evidence for prone positioning has evolved significantly over time:

• Earlier meta-analyses (pre-2013) showed improved oxygenation but failed to demonstrate consistent mortality benefits 1
• More recent evidence strongly supports prone positioning for severe ARDS:
  • The PROSEVA trial demonstrated significant mortality reduction when prone positioning was applied for at least 16 hours per day in patients with severe ARDS 1, 3
  • Meta-analyses of trials using prolonged prone positioning (≥12 hours daily) show a 26% relative risk reduction in mortality (RR 0.74; 95% CI 0.56-0.99) 5
  • The mortality benefit is most pronounced in patients with moderate to severe ARDS (PaO2/FiO2 <150 mmHg) 5

Implementation Protocol

For optimal results, prone positioning should be implemented as follows:

1. Patient selection: Patients with severe ARDS (PaO2/FiO2 <150 mmHg) 1, 2, 5
2. Timing: Early application within the first 48 hours of ARDS diagnosis 1
3. Duration: At least 16-20 hours per day 1, 2
4. Staffing: Requires well-trained staff (at least one doctor and three nurses) following a standardized protocol 4
5. Concurrent strategies: Should be combined with lung-protective ventilation (tidal volume 6 mL/kg predicted body weight, plateau pressure <30 cmH2O) 2

Contraindications and Complications

Contraindications:

• Open abdominal wounds
• Unstable pelvic fractures
• Spinal lesions or instability
• Brain injury without intracranial pressure monitoring 1

Potential Complications:

• Endotracheal tube obstruction or dislocation
• Pressure sores
• Accidental removal of vascular lines 4, 5

However, when performed by experienced staff following standardized protocols, serious adverse events are rare 4.

Special Considerations

• Prone positioning can be safely combined with other rescue therapies such as ECMO in severe cases 4
• For patients not responding to prone positioning alone, consider neuromuscular blockade for the first 48 hours to prevent patient-ventilator dyssynchrony 1, 2
• Prone positioning may be more effective than other rescue therapies for refractory hypoxemia, with stronger evidence for mortality benefit 6

Practical Implementation Tips

• Use adequate sedation to ensure patient comfort and prevent self-extubation
• Carefully secure all tubes and lines before turning
• Monitor for pressure injuries, particularly at facial pressure points
• Return to supine position if life-threatening complications occur (hemodynamic instability, cardiac arrest)
• Continue prone positioning daily until significant improvement in oxygenation is maintained in supine position (PaO2/FiO2 >150 mmHg with PEEP <10 cmH2O and FiO2 <0.6 for at least 4 hours after supine repositioning) 1

In summary, prone positioning represents one of the few interventions in ARDS management with proven mortality benefit when applied appropriately to patients with severe disease.