- Remember, you have no outward way of visualizing chest rise on HFOV,
so without a CXR, you have no idea how over/under inflated you are.
Ventilation (ΔP)
Increasing the ΔP will increase the amplitude of the oscillator’s diaphragmatic
movement, and thus increase tidal volume leading to better
CO 2 removal. Because of the respiratory cycle in HFOV, a change in ΔP
yields a geometric change in ventilation in the direction of the change.
You can think of it much as you do adjusting the rate on CMV.^
- Increase in ΔP
↓CO 2 )
→ (^) geometric increase in ventilation (will
- Decrease in ΔP
↑CO 2 )
→ geometric decrease in ventilation (will
NOTE: If MAP is decreased too rapidly, atelectasis may develop and lead to ↑CO 2
Ventilation (Hz)
If efforts to alter ventilation with adjustments in the ΔP are unsuccessful, we
will sometimes alter the Hz. Changes in the Hz actually alter the respiratory
cycle itself. This change in the cycle of ventilation causes the relationship of
Hz to ventilation to roughly be as follows:
- Increase in Hz → linear DECREASE in ventilation (will ↑CO 2 )
- Decrease in Hz → linear INCREASE in ventilation (will↓CO 2 )
Think of adjusting the Hz in the direction you want the CO 2 to go.