High frequency ventilation (HFV) uses very high rates of breathing (2.5-15 Hz) combined with low tidal volumes (0.5-5 ml/kg). There are several types of HFV including high frequency oscillatory ventilation and high frequency jet ventilation. HFV works through mechanisms like convection, pendelluft effect, and molecular diffusion to improve gas exchange with small tidal volumes. It allows adequate gas exchange and oxygenation using lower airway pressures, reducing the risk of lung injury. Settings like mean airway pressure, amplitude, and frequency are adjusted based on the patient's oxygenation and ventilation needs. HFV is effective for various lung conditions but requires careful monitoring to optimize outcomes.

2. Introduction
 High frequency ventilation (HFV) is defined by the
‘high frequency’ (2.5-15 Hz) and low tidal volume
(0.5-5 ml/kg).
 Types of HFV
 High Frequency Oscillatory Ventilation
 High Frequency Jet Ventilation
 High Frequency Positive Pressure Ventilation

3. Types of High Frequency
Ventilators
 High frequency jet ventilators (HFJV)
 Bunnel Life Pulse; Acutronic (Switzerland)
 True high frequency oscillatory ventilators (HFOV)
 Sensor Medics 3100A; Hummingbird & Humming V;
 Stephan SHF 3000; Dufour OHF 1
 Oscillator-like devices
 Infant Star HFV (HFFI); SLE 2000 HFO; Dräger Baby Log
8000

4. HFPPV
 Are conventional ventilators adapted to operate at
rapid rates between 60 – 120
 Are not used frequently

5. HFOV
 Essentially airway vibrators
 characterized by having both active inspiratory and
expiratory phases
 A continuous flow of gas generates oscillations
 Pressure oscillations within the airway produce small
tidal volumes
 Regular ET tubes can be used

6. Advantages over conventional
ventilation
 Ability to provide adequate gas exchange using lower
proximal airway pressures
 Reduces volutrauma and barotrauma
 Preservation of normal lung architecture in the
relatively intact lung even when high mean airway
pressures are necessary

7. Mechanism of HFOV
 Lungs as a two compartment model
 First compartment: AIRWAYS.
 Do not participate in gas exchange
 referred as anatomic dead space
 Second compartment: ALVEOLAR UNITS
 responsible for gas exchange

8.  Elements of HFV
 Use of supraphysiologic ventilatory rates above 60 rpm
 Use of tidal volume smaller than the anatomic dead
space
 6 mechanisms for gas exchange have been noted with high
frequency ventilation

9. How does HFV work?
 Convection (Bulk Flow) Ventilation
 Even with small tidal volumes, direct alveolar ventilation
occurs to short path length units that branch off of the
primary airways.

10. How Does HFV Work?
 Taylor Dispersion:
 Convective flow
superimposed on a diffusive
process, results in
increased dispersion of the
tracer molecules.
 The high velocity spike of
gas moves down the center
of the tube, leaving the
molecules on the periphery
unmoved. Gas diffuses
evenly through the tube
when flow stops.

11. How Does HFV Work?
 Pendeluft
– At high frequencies,
distribution becomes
strongly influenced by
time constant
inequalities. Gas from
fast units (short time
constants) will empty
into the slow (long time
constants) units.

12. How Does HFV Work?
 Cardiogenic Mixing:
 The heart beat adds to the the peripheral gas mixing.

13. How Does HFV Work?
 Molecular Diffusion:
– Is felt to be one of the major
mechanisms for gas exchange in
the alveolar regions.
– It is responsible for the gas
exchange across the AC
membrane and also contributes
to the transport of O2 and CO2
in the gas phase near the
membrane.
– This may be due to the increased
turbulence of molecules.

14. during HFV2
(1) Direct ventilation of most proximal alveoli units by bulk
convection
(2) Pendalluft effect – asynchronous flow among alveoli due
to asymmetries in airflow impedance. This cause gas to recirculate
among lung units and improve gas exchange
(3) Turbulence in the large airways causing enhanced gas
mixing
(4) Turbulent flow with lateral convective mixing
(5) Taylor dispersion – laminar flow with lateral transport by
diffusion
(6) Collateral ventilation through non-airway connections
between neighbouring alveoli
(7) Asymmetric velocity profiles – convective gas transport is
enhanced by asymmetry between inspiratory and expiratory
velocity profiles that occur at branch points in the airways.
Proposed mechanisms that can
enhance gas exchange

17. Switch from conventional to HFV
 Goal of HFV:
 maximize oxygenation and ventilation with
adequate lung volume while minimizing
barotrauma and oxygen toxicity
 Indications:
 increased FiO2 and MAP and with poor
saturations. (O2 index)
 higher pressures on conventional ventilation

18. Indications
 Rescue following failure of conventional ventilation
 PPHN, Meconium
 Air leak syndromes
 Pneumothorax, pulmonary interstitial emphysema
 To reduce barotrauma when conventional ventilator
settings are high
 Hyaline membrane disease
 Diaphragmatic hernia
 Pulmonary hypoplasia
 Alternative to ECMO

19. Contraindications for HFV
 Obstructive Airway Disease
 Asthma/RAD
 Emphysema
 Bronchiolitis
 Cardiovascular System Dysfunction
 Shock

20. Terminology
 Frequency - High frequency ventilation rate (Hz,
cycles per second)
 MAP- Mean airway pressure (cmH2O)
 Amplitude- delta P ( analogous to PIP on conventional
ventilation)
 FiO2

21.  Oxygenation
 is dependent on MAP and FiO2
 MAP provides a constant distending pressure equivalent
to CPAP. This inflates the lung to a constant and optimal
lung volume maximizing the area for gas exchange and
preventing alveolar collapse in the expiratory phase.
 Ventilation
 is dependent on amplitude( delta P) and frequency
 Thus when using HFV CO2 elimination and
oxygenation are independent

22. Initial settings
 Frequency : The smaller the Hz number, the larger the tidal
volume.
 set at 15 Hz for premature with RDS and 10 Hz for larger babies
 1000 grams -15 Hz
 1000-2000 grams - 12 Hz
 2.0-10 Kg - 10 Hz
 For Meconium Aspiration Syndrome - 3-6 Hz
 MAP : is set at the same or higher levels depending on the
strategy
 Amplitude/delta P : at 25 – 30 and adjusted depending on PaCo2
 FIO2 : 1.0

23. Type of Strategies
 High volume strategy
(aim to maximize
recruitment of alveoli)
 Set MAP 2-3 cmH2O
above the MAP on
conventional ventilation
 Set frequency to 10 Hz
 MAP in 1-2 cmH2O
steps until oxygenation
improves
 Low volume strategy
(aim to minimize lung
trauma)
 Set MAP equal to the
MAP on conventional
ventilation
 Set frequency to 10 Hz
 Adjust amplitude( delta
P) to get an adequate
chest wall vibration.

24.  In homogeneous lung disease, high volume HFOV at low
inspired oxygen concentrations, and evidence supports it as
the preferred strategy.
 In surfactant deficient, “high volume” HFOV resulted in
significantly less lung damage than either IPPV or low
volume HFOV strategy
 There have been no large randomized clinical studies
comparing the two HFOV strategies, but a reduction in
CLD has only been noted in trials in which the “high
volume strategy” was used

25. Monitoring
 Clinical : Visibly assess the chest vibration/wiggle
 Wiggle should extend up to umbilicus
 Vibration mainly in the neck could indicate a dislodged
ET tube
 Asymmetry of vibration could indicate Pneumothorax
 ABG : monitoring is required frequently at first to assess
effectiveness
 Monitoring Vitals :
 tachycardia; decreased peripheral pulse; peripheral
shutdown; decreased blood pressure and desaturations
indicate hyperinflation

26. Monitoring
 CXR : to assess the degree of lung distension
 Initial x-ray at 1-2 hrs to determine the baseline lung
volume on HFV (aim for 7-8 ribs).
 A follow-up chest x-ray in 4-6 hours is recommended to
assess the expansion.
 Thereafter repeat chest x-ray with acute changes in
patient condition.
 Over inflation : X-ray reveals diaphragm flattened,
lung fields expanded to greater than 8th rib posteriorly,
thin cardiac silhouette.
 Under inflation : X-ray reveals lungs fields "whiteout"
and expanded to less than 6th rib posteriorly

27. Optimizing settings
 Oxygenation problem
 Poor Oxygenation
 Increase FiO2
 Increase MAP(1-2cmH2O)
 Perform a chest x-ray to check the appearance
 If over distension - reduce MAP
 If under distension - increase MAP
 Measure BP as hypotension due to hypovolaemia may
occur during HFOV
 Over Oxygenation
 DecreaseFiO2
 Decrease MAP(1-2cmH2O)

28. Optimizing settings
 Ventilation
 High Paco2
 Check the chest wall is "bouncing".
 Check that the largest possible sized endotracheal
tube has been used.
 Increase Amplitude
 Decrease Frequency (1-2Hz) if Amplitude Maximal
 Low paco2
 Decrease Amplitude
 Increase Frequency (1-2Hz)if Amplitude Minimal

29. Weaning
 Reduce FiO2 to <40% before weaning MAP
 Reduce MAP when chest x-ray shows evidence of over-
inflation (>9 ribs).Reduce MAP in 1-2cm increments to 8-9.
 In air leak syndromes (low volume strategy), reducing MAP
takes priority over weaning the FiO2.
 Wean the amplitude in 4cm H2O increments.
 Do not wean the frequency
 Consider switching to conventional ventilation when MAP
<10cm H2O, Amplitude 20-25 and blood gases satisfactory

30. Adverse effects
 Hyperinflation : may result and manifest by decreased cardiac
output recognized by: tachycardia; decreased peripheral pulse;
peripheral shutdown; decreased blood pressure and
desaturations.
 Pneumothorax : signs may be gradual occurring over several
hours. Indications are deterioration of blood gas and saturation
levels and decreased vibrations on affective side.
 Increased risk of dislodgment of ET tube due to the short rigid
vibrating tubing.
 The association between HFOV and IVH remains open. Studies
report varying IVH rates of this multifactorial complication.
 Airway damage : tracheitis ( MC – HFJV)

31. Practical points
 Position the infant's body in alignment with the oscillator
so that only the head is being moved when it is time for a
position change
 Do not disconnect tubing during repositioning.
 Disconnection is discouraged as it can cause alveolar
collapse and loss of lung volume.
 Use of Neopuff is discouraged unless mechanical failure or
severe deterioration of infant's condition.
 Infants should not be weighed on HFOV routinely.
 Turn oscillations off at start/stop knob briefly while X-ray
is taken

32. SUCTIONING
 Suction before putting on HFO
 Avoid for the next 4 hrs –preferably up to 24 hrs
 Inline suctioning
 Suctioning causes de recriutment.
 Increase the MAP by 2 then slowly come back to
original in 10- 15 min

33. Practical points
 Monitoring of infant’s heart rate may be problematic via
ECG electrodes, heart rate can be monitored as a ‘pulse’
through the UAC .
 Evaluation for heart murmurs may require a temporary
pause in HFOV therapy.
 Assess infant’s neurological and behavioral state on HFOV.
 Analgesia and sedation may be required for comfort and
avoidance of ET tube dislodgment

34. strategies
 RDS
 < 1000 GM – 12 Hz
 MAP- 3-5 above the CVent
 Delta P – wiggle
 PIE
 MAP< 1-2 CVent
 AIR LEAK
 MAP= OR 1-2 > CVent

35. New trends for HFV
 HFV and Nitric Oxide
 HFOV and Surfactant
 HFOV and Partial Liquid Ventilation

36. Thank you