Can low frequencies (5-6 Hz) in High Frequency Oscillatory Ventilation (HFOV) cause lung damage in preterm infants due to high tidal volumes?

Low Frequencies in High Frequency Oscillatory Ventilation Can Damage Preterm Infant Lungs

Low frequencies (5-6 Hz) in High Frequency Oscillatory Ventilation (HFOV) can indeed damage the lungs of preterm infants due to higher tidal volumes, and higher frequencies (15-18 Hz) with lower tidal volumes should be used instead. 1

Mechanism of Lung Injury with Low Frequencies

When using HFOV in preterm infants, the relationship between frequency and tidal volume is inverse - lower frequencies are associated with higher tidal volumes. This relationship creates significant risk for lung injury:

• Lower frequencies (5-6 Hz) require higher tidal volumes to maintain adequate ventilation
• Higher tidal volumes can cause:
  • Volutrauma (stretch injury to lung tissue)
  • Increased risk of air leaks
  • Impaired gas exchange
  • Development of bronchopulmonary dysplasia (BPD)

Optimal HFOV Parameters for Preterm Infants

Recent evidence supports using higher frequencies with lower tidal volumes:

• Optimal frequency range: 15-18 Hz (median 16 Hz) 1
• Optimal tidal volume: Approximately 1.6 ml/kg (median 1.63 ml/kg) 1
• Strategy: Low volume, high frequency approach

This approach has been shown to provide adequate ventilation while minimizing lung injury in preterm infants with respiratory distress syndrome 1, 2.

Clinical Evidence Supporting Higher Frequencies

The 2018 study in preterm lambs demonstrated that proper lung recruitment strategies during HFOV optimize gas exchange and reduce pneumothorax risk 3. A 2020 study showed that early use of HFOV with higher frequencies (above 15 Hz) and lower tidal volumes was associated with increased survival without bronchopulmonary dysplasia in preterm infants 2.

Guidelines for HFOV Use in Neonates

The Paediatric Mechanical Ventilation Consensus Conference (PEMVECC) acknowledges HFOV as a reasonable alternative mode of ventilation when poor lung compliance, low volumes, and poor gas exchange complicate the clinical course 4. However, the guidelines emphasize:

• Avoiding excessive chest wall movement during ventilation of preterm infants 4
• Individualizing peak inflating pressures with each breath 4
• Minimizing peak inspiratory pressure to reduce ventilator-associated acute lung injury 4

Practical Application of HFOV in Preterm Infants

When initiating HFOV in preterm infants:

1. Start with higher frequencies (15-18 Hz) to minimize tidal volume requirements
2. Target low tidal volumes (approximately 1.6 ml/kg)
3. Use appropriate mean airway pressure to maintain lung volume without overdistension
4. Monitor for signs of inadequate ventilation or overdistension:
   • Chest wall vibration
   • Gas exchange parameters
   • Hemodynamic stability

Common Pitfalls to Avoid

1. Using adult-derived HFOV settings in neonates - Neonatal lungs require different parameters
2. Selecting low frequencies (5-6 Hz) - This increases tidal volumes and risk of lung injury
3. Inadequate monitoring - Continuous assessment of ventilation adequacy is essential
4. Failure to adjust parameters based on clinical response and lung mechanics

Conclusion

The evidence strongly supports using higher frequencies (15-18 Hz) with lower tidal volumes during HFOV in preterm infants to minimize lung injury. The practice of using low frequencies (5-6 Hz) should be avoided due to the associated higher tidal volumes and increased risk of lung damage.