What is the open lung concept in Pediatric Acute Respiratory Distress Syndrome (PARDS)?

The Open Lung Concept in Pediatric Acute Respiratory Distress Syndrome (PARDS)

The open lung concept in PARDS is a ventilation strategy that aims to recruit collapsed alveoli and maintain their patency through optimized PEEP titration and recruitment maneuvers, while preventing ventilator-induced lung injury by using low tidal volumes and limiting plateau pressures. 1

Core Components of the Open Lung Concept

PEEP Titration and Recruitment

• PEEP should be individualized based on PARDS severity 2:

  • Mild PARDS (PaO₂/FiO₂ 201-300 mmHg): Lower PEEP (5-10 cmH₂O)
  • Moderate PARDS (PaO₂/FiO₂ 101-200 mmHg): Higher titrated PEEP
  • Severe PARDS (PaO₂/FiO₂ ≤100 mmHg): Higher titrated PEEP with consideration for prone positioning and neuromuscular blockade

• Recruitment maneuvers may be considered in cases of severe refractory hypoxemia despite optimized PEEP 1

  • Types include:
    • Brief application of continuous positive airway pressure (30-40 cmH₂O)
    • Progressive incremental increases in PEEP at constant driving pressure
    • Brief high driving pressures

Lung-Protective Ventilation Parameters

• Low tidal volumes: 4-8 mL/kg predicted body weight 1
• Plateau pressure limit: ≤28-32 cmH₂O (depending on chest wall compliance) 2
• Driving pressure (Plateau pressure - PEEP): Keep as low as possible 1
• Permissive hypercapnia: Target pH >7.20 2

Evidence and Effectiveness

The open lung concept is based on the understanding that PARDS involves heterogeneous lung injury with areas of collapsed alveoli alongside normally aerated regions. This approach aims to:

1. Prevent atelectrauma: Cyclic opening and closing of alveoli causes shear stress and inflammation 2
2. Reduce ventilator-induced lung injury: By limiting excessive pressure and volume 2
3. Improve ventilation-perfusion matching: By recruiting collapsed lung units 1

However, the evidence supporting specific recruitment strategies in PARDS is limited. The Pediatric Mechanical Ventilation Consensus Conference (PEMVECC) states there are "insufficient data to recommend any lung recruitment manoeuvre in children with lung injury" 2. Despite this, they suggest considering PEEP titration and lung recruitment in patients with moderate-to-severe disease 2.

Implementation Considerations

Patient Selection

Not all PARDS patients benefit equally from open lung strategies. Patients with:

• Non-focal ARDS patterns on imaging
• Lower PaO₂/FiO₂ ratios
• Non-pulmonary causes of ARDS

May have more recruitable lung tissue and respond better to this approach 2.

Monitoring Response

When implementing the open lung concept:

• Monitor oxygenation (SpO₂, PaO₂/FiO₂)
• Assess lung compliance
• Watch for hemodynamic compromise during recruitment maneuvers
• Discontinue recruitment if blood pressure drops or oxygenation worsens 1

Oxygenation Targets

For PARDS patients, target:

• SpO₂ 92-97% when PEEP <10 cmH₂O
• SpO₂ 88-92% when PEEP ≥10 cmH₂O 2

Pitfalls and Caveats

1. Hemodynamic instability: High PEEP and recruitment maneuvers can reduce venous return and cardiac output
2. Barotrauma risk: Excessive pressure during recruitment can cause pneumothorax
3. Misclassification of ARDS morphology: Applying inappropriate ventilation strategies based on incorrect assessment of lung morphology (focal vs. non-focal) can increase mortality 2
4. Mechanical power: The combination of pressure, volume, flow, and respiratory rate contributes to ventilator-induced lung injury; consider the cumulative effect of ventilation parameters 2

Future Directions

Research is needed to:

1. Develop better methods to identify patients who will benefit from open lung strategies
2. Establish optimal recruitment protocols specific to pediatric patients
3. Determine the role of imaging in guiding personalized ventilation strategies 2, 3

The PROSpect trial is expected to provide more evidence on optimal ventilation strategies for severe PARDS 3.