What strategy should be used to lower respiratory complications in a patient on BiPAP (Bilevel Positive Airway Pressure) with high FiO₂ (Fraction of Inspired Oxygen) who remains hypoxic?

Decrease Tidal Volume Permitting Mild Hypercapnia (Answer C)

The correct strategy is to decrease tidal volume and permit mild hypercapnia (permissive hypercapnia), as this lung-protective ventilation approach reduces mortality and prevents ventilator-induced lung injury in patients with acute lung injury/ARDS. 1

Rationale for Permissive Hypercapnia Strategy

Lung-protective ventilation with low tidal volumes (approximately 6 mL/kg ideal body weight) and permissive hypercapnia is the evidence-based standard for mechanically ventilated patients with ALI/ARDS who have high inspiratory pressures or are at risk for barotrauma/volutrauma. 1 This strategy:

• Reduces tidal volume and minute ventilation to prevent alveolar overdistension and perpetuation of lung injury 1
• Has been shown to be safe and effective at reducing mortality without adverse consequences 1
• Maintains end-inspiratory plateau pressures at levels less than 30 cmH₂O 1
• Allows PaCO₂ to rise while maintaining arterial pH above 7.20 1

The upper limit for PaCO₂ has not been definitively established, but normalization of arterial blood gas values is not considered a valuable therapeutic maneuver in this context. 1

Why Other Options Are Incorrect

Option A (Hyperventilate to Normalize CO₂) - WRONG

• Hyperventilation with high tidal volumes increases the risk of ventilator-induced lung injury through barotrauma and volutrauma 1
• Normalization of CO₂ is not a therapeutic goal in ARDS patients 1
• This approach contradicts lung-protective ventilation principles 1

Option B (Low PEEP to Prevent Barotrauma) - WRONG

• In patients requiring high FiO₂ (>0.60), higher PEEP levels (10-15 cmH₂O) are recommended for moderate to severe ARDS to recruit collapsed alveoli and improve oxygenation 2
• Low PEEP fails to prevent atelectrauma from repeated alveolar collapse and reopening 2
• PEEP selection should be based on gas exchange, hemodynamic status, and lung recruitability, not arbitrarily kept low 2

Option D (Increase Tidal Volume to Increase PCO₂ Clearance) - WRONG

• Increasing tidal volume directly contradicts lung-protective ventilation and increases mortality risk 1
• Higher tidal volumes cause alveolar overdistension and systemic cytokine-mediated organ dysfunction 1
• This approach increases plateau pressures above the safe threshold of 30 cmH₂O 1

Additional Management Considerations

For this hypoxic patient on BiPAP with high FiO₂:

• Consider prone positioning if PaO₂/FiO₂ ratio is ≤100 mmHg, as this improves oxygenation in approximately 65% of ARDS patients 1
• If BiPAP fails (persistent hypoxemia despite optimization), proceed to endotracheal intubation and mechanical ventilation with lung-protective settings 1
• Monitor for BiPAP failure closely, as delayed intubation is associated with increased mortality 1

Common Pitfalls to Avoid

• Do not delay intubation in patients failing noninvasive ventilation, as this increases mortality risk 1
• Do not use high tidal volumes (>8 mL/kg predicted body weight) even if hypercapnia develops, as this increases mortality 1
• Do not attempt to normalize blood gases at the expense of lung-protective ventilation parameters 1
• Ensure arterial pH remains >7.20 when permitting hypercapnia 1