1. Theory of HFV

2. High Frequency Ventilation
Defined by FDA as a ventilator that delivers more than 150 breaths/min.
Delivers a small tidal volume, usually less than or equal to anatomical dead space volume.
While HFV’s are frequently described by their delivery method, they are usually classified by their exhalation mechanism (active or passive).

3. Differences between HFOV and CMV
CMV HFOV
Rates
Tidal Volume ml/kg ml/kg
Alv Press 0 - > 50 cmH2O cmH2O
End Exp Vol Low Normalized

4. HFV Gas Exchange
Henderson first published his findings in 1915, assessing dead space relationship in ventilation.
He stated, “there may easily be a gaseous exchange sufficient to support life even when Vt is considerably less than dead space.”

5. HFV Gas Exchange
In the 1970’s, Bunnell and his associates demonstrated in animals that adequate alveolar ventilation could be achieved with a frequency between Hz and a Vt of % less volume than anatomical dead space.
Slutsky, et al. theorized that the gas exchange mechanism was caused by the “coupled effects” of convection and molecular diffusion.

6. HFV Gas Exchange
Chang theorized that convective processes were more predominant with an increase in Vt and lower frequencies. A diffusive mechanism may be more predominant where there is a decrease in Vt and higher frequencies are used.

7. High Frequency Ventilation
Types of HFV’s Approved for use in both Neonates and Pediatrics
SensorMedics 3100A HFOV
Bird Volumetric Diffusive HFPPV
Types of HFV’s Approved for use in Neonates Only
Bunnell Life Pulse HFJV
Infrasonics Infant Star (discontinued) HFFI

8. Bunnell Life Pulse Jet
Delivers a pulse of gas into the ETT via a special adapter and pinch valve mechanism
Exhalation is Passive
Frequency of Hz
Peak Airway Pressure of
8- 50 cmH2O
Used in tandem with a
conventional ventilator
Mean Airway Pressure limited to conventional ventilator capabilities

9. Infrasonics Infant Star HFFI
Modification of the conventional Infant Star
Facilitated/Passive Exhalation
Pressure waveform manipulated by a series of pneumatic valves
Frequency of Hz
Paw cannot be adjusted directly. Usually adjusted by changing end expiratory pressure on CMV (limited to 24 cmH2O)
Fixed 18 ms inspiratory time

10. Bird Volumetric Diffusive Vent
A pneumatic cartridge (Phasitron) interrupts the pressurized gas source
Passive Exhalation
Frequency of Hz
Paw is not directly adjusted
May deliver HFV on top of a conventional breath

11. Sensor Medics 3100A
Electrically powered, electronically controlled piston-diaphragm oscillator
Paw of cmH2O
Pressure Amplitude from cmH2O
Frequency of Hz
Inspiratory Time 30% - 50%
Flow rates from LPM

12. 3100A
“True” Oscillator
Produces an active exhalation, and does not depend on passive recoil of the chest for CO2 removal
Stand Alone Ventilator
Does not require nor deliver a conventional breath through the system
Does not require a special ET tube

13. Volume delivery and MAP

14. Comparison: Volume delivery

15. 3100A Ventilator
Approved in 1991 for Neonatal Application for the treatment of all forms of respiratory failure.
Approved in 1995 for Pediatric Application, with no upper “weight limit”. For treating selected patients failing conventional ventilation.

16. Remember
Each device has specific labeling restrictions for its use. Many devices are classified as “RESCUE ONLY” or for treating only a specific pathology.
No clinical comparisons between devices.
Each has its own indications and risks.
Strategies to treat each disease process is specific to the device used.