Why is high frequency oscillatory ventilation (HFOV) with low frequencies used to manage pulmonary interstitial emphysema in extreme preterms?

High Frequency Oscillatory Ventilation with Low Frequencies for Pulmonary Interstitial Emphysema in Extreme Preterm Infants

High frequency oscillatory ventilation (HFOV) with low oscillatory frequencies (5-6 Hz) is specifically recommended for managing pulmonary interstitial emphysema (PIE) in extreme preterm infants when conventional ventilation fails. 1

Pathophysiological Rationale

HFOV with low frequencies is particularly beneficial in PIE for several key reasons:

• Extended expiratory time: Lower frequencies (5-6 Hz) provide a prolonged expiratory phase, which allows trapped air to escape from the interstitial spaces 2
• Reduced barotrauma: HFOV delivers very small tidal volumes at higher mean airway pressures, minimizing additional lung injury 3
• Improved gas trapping resolution: The oscillatory pattern helps mobilize trapped air while maintaining adequate gas exchange 2

Clinical Evidence

The most recent evidence strongly supports this approach:

• A retrospective cohort study demonstrated that HFOV with low frequency (5-6 Hz) resulted in:

  • Rapid and sustained improvement in oxygenation in infants with bilateral PIE
  • Successful resolution of unilateral PIE through controlled collapse and re-inflation
  • 79% overall survival rate (15/19 infants), including 71% of bilateral PIE cases 2

• This approach allows for reduction in mean airway pressure over time (from 14 ± 3.9 cm H₂O at baseline to 12 ± 2.9 cm H₂O at 72 hours) while improving oxygenation 2

Implementation Algorithm

When managing extreme preterm infants with PIE:

1. Initial assessment: Confirm PIE diagnosis radiologically and assess severity based on:

   • Oxygen requirements (high FiO₂)
   • Persistent respiratory acidosis
   • Extent of disease (bilateral vs. unilateral)

2. Transition to HFOV with low frequency settings:

   • Frequency: 5-6 Hz
   • Inspiratory time: 30%
   • Begin with mean airway pressure similar to conventional ventilation

3. Monitoring and adjustment:

   • Monitor oxygenation, ventilation, and hemodynamic parameters closely
   • For bilateral PIE: Gradually reduce mean airway pressure as tolerated
   • For unilateral PIE: Consider positioning with affected side dependent to promote selective atelectasis

4. Duration of therapy:

   • Continue for at least 24-72 hours to achieve sustained improvement
   • Transition back to conventional ventilation only after radiological improvement

Special Considerations

• Contraindications: HFOV should not be used in obstructive airway disease due to risk of dynamic hyperinflation 3

• Cautions:

  • Particular caution in infants with cardiac dysfunction or passive pulmonary blood flow 3
  • Monitor for complications including hypotension, bleeding diatheses, bronchopulmonary dysplasia, and necrotizing tracheobronchitis 4

• Alternative approaches: If HFOV fails, consider high-frequency jet ventilation (HFJV), which has shown superior outcomes compared to conventional ventilation in a multicenter trial (61% vs 37% success rate) 5

• ECMO consideration: For refractory cases where available, ECMO may be considered as a rescue therapy 3

Conclusion

While adult guidelines recommend against routine use of HFOV in ARDS 3, neonatal evidence supports HFOV with low frequencies as an effective strategy specifically for PIE in extreme preterm infants. The physiological benefit comes from the extended expiratory time allowing trapped air to escape, while maintaining adequate gas exchange with minimal additional lung injury.