In High Frequency Oscillation, tidal volumes per piston movement are typically what percent of anatomic or mechanical dead space?

• A. 5-10%
• B. 20-80%
• C. 90-100%
• D. 100-150%

Answer: (B)

In High Frequency Oscillation Ventilation, the volume delivered with each piston movement is kept very small relative to the lung’s dead space. Clinically, the tidal volume per oscillation is typically about 20% to 80% of the anatomic or mechanical dead space. This means each stroke moves roughly 0.4–1.6 mL/kg in a typical neonate, depending on size and setup.

Why that range fits: using small tidal volumes minimizes volutrauma while still allowing effective gas exchange through the combination of high oscillation frequency, continuous mean airway pressure, and gas mixing within the lungs. Gas exchange in HFOV relies more on diffusion, pendelluft, and high-frequency movement than on bulk alveolar ventilation, so a small tidal volume is sufficient when delivered at very high frequency.

If the tidal volume were much smaller (e.g., a tiny fraction of dead space), CO2 clearance would be inadequate at typical frequencies. If it were much larger (approaching or exceeding dead space), the risk of volutrauma and lung injury would rise. The 20–80% range represents the balance used to achieve ventilation while protecting the lungs.