Theory of HFV

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Theory of HFV
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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 HFVs are frequently described by their
  delivery method, they are usually classified by
  their exhalation mechanism (active or passive).

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Differences between HFOV and CMV
CMV HFOV Rates 0 - 150 180 - 900 Tidal
Volume 4 - 20 ml/kg 0.1 - 5 ml/kg Alv Press 0 -
gt 50 cmH2O 0.1 - 5 cmH2O End Exp
Vol Low Normalized
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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.

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HFV Gas Exchange

• In the 1970s, Bunnell and his associates
  demonstrated in animals that adequate alveolar
  ventilation could be achieved with a frequency
  between 5 - 30 Hz and a Vt of 20 - 25 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.

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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.

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High Frequency Ventilation

• Types of HFVs Approved for use in both Neonates
  and Pediatrics
• SensorMedics 3100A HFOV
• Bird Volumetric Diffusive HFPPV
• Types of HFVs Approved for use in Neonates Only
• Bunnell Life Pulse HFJV
• Infrasonics Infant Star (discontinued) HFFI

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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 4 - 11 Hz
• Peak Airway Pressure of
• 8- 50 cmH2O
• Used in tandem with a
• conventional ventilator
• Mean Airway Pressure limited to conventional
  ventilator capabilities

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Infrasonics Infant Star HFFI

• Modification of the conventional Infant Star
• Facilitated/Passive Exhalation
• Pressure waveform manipulated by a series of
  pneumatic valves
• Frequency of 2 - 22 Hz
• Paw cannot be adjusted directly. Usually adjusted
  by changing end expiratory pressure on CMV
  (limited to 24 cmH2O)
• Fixed 18 ms inspiratory time

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Bird Volumetric Diffusive Vent

• A pneumatic cartridge (Phasitron) interrupts the
  pressurized gas source
• Passive Exhalation
• Frequency of 1.6 - 21.6 Hz
• Paw is not directly adjusted
• May deliver HFV on top of a conventional breath

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Sensor Medics 3100A

• Electrically powered, electronically controlled
  piston-diaphragm oscillator
• Paw of 3 - 45 cmH2O
• Pressure Amplitude from 8 - 110 cmH2O
• Frequency of 3 - 15 Hz
• Inspiratory Time 30 - 50
• Flow rates from 0 - 40 LPM

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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

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Volume delivery and MAP
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Comparison Volume delivery
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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.

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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.