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HFOV
HIGH FREQUENCY OSCILLATORY VENTILATION
B EC KY VA R EL A & JA MIE WOOD
Overview
 High Frequency Ventilation (HFV)
 High Frequency Oscillatory Ventilation (HFOV) and how it works
 When do we use HFOV
 Basic Parameters for HFOV
 How HFOV prevents Ventilator Induced Lung Injury (VILI)
High Frequency Ventilation
Provides augmented gas distribution
By means of numerous gas transport
mechanisms.







Convection, transit time, direct ventilation
Pendalluft effect
Taylor dispersion
Asymmetric velocity
Cardiogenic Mixing
Molecular diffusion
Collateral Ventilation
Convection, Transit Time and
Direct Ventilation
Convection
 is the transport of air flow at a
constant equal velocity that is
parabolic in shape.
Transit Time:
 Airflow to the alveoli will vary
in proportion to the length of
the Bronchial airways.
Direct Ventilation:
 Results from bulk air flow to
alveoli that have a much
shorter transit time.
Pendalluft Effect
Taylor Dispersion
Asynchronous Filling
At the end of expiration:
• Alveoli with short time constants
(fast alveoli units) are empty.
• Alveoli with longer time constants
(slow alveoli units) are still
emptying
Asynchronous filling:
• Gases will move from slow units
to fast units because of pressure
gradients between the alveoli.
The relationship between:
 Axial velocity profile (Turbulence)
 the diffusion of gases in motion
 and the branching network of the
lungs.
Asymmetry
Airflow moving through the airways
moves in a u-shape formation. At the
center of the lumen air will move at a
faster velocity, than air that is closest
to the wall.
Asymmetry
Occurs with rapid respiratory cycles.
Gases (O2) at the center of the lumen
will advance further into the lungs as
gases (CO2) along the wall of the
airway moves out towards the mouth.
Cardiogenic Mixing
As the heart beats the heart
provides additional peripheral
mixing by exerting pressure
against the lungs during
contraction of the heart.
This pressure promotes the
movement of gas flow through
the neighboring parenchymal
regions.
Molecular Diffusion
Maintaining a constant
distending pressure with HFV
within the lungs along with
movement of gas molecules
promotes gas diffusion across
the alveolar membrane, at a
faster rate.
Collateral Ventilation
Collateral ventilation
increases with HFV due to
connections between the
alveoli
 (Pores of Kohn)
What is HFOV
 HFOV has all of the elements of high
frequency ventilation discussed
previously.
 Also provides a bias oscillatory gas flow
used to generates positive and negative
pressure fluctuations referred to as
amplitudes or (Delta-P)
How does it work?
 Small tidal volumes at high frequency are
generated by low amplitude pressure
oscillations. These tidal volumes that are
approximately equal to dead space.
 High mean airway pressures (PEEP)
provides distending pressure.
 HFOV can provide 5-15 Hz equal to (900
breaths/min.
Oscillation/Frequency Hz
Amplitude
MAP/PEEP
HFOV: 3100A
External Air/O2 Blender
1. Provides blended air/O2 and cooling to the
oscillator
External Humidifier
1. Attaches and functions with the
patient’s circuit
2. Capable of flows up to 40 LPM
Pneumatic Logic and Control
System
Comprised of 4 pneumonic controls
1. Bias flow
2. Mean Pressure adjustments
3. Mean pressure limit control
4. Patient circuit calibration adjustment
Patient Circuit
Provides:
1. Bias flow/pressure
2. Pressurized oscillations
3. Pressure limiting
Oscillator Subsystem
Uses an
1.electronic control circuit called the
square wave form driver
2. Forward and backward linear motion
provides inspiratory and expiratory gas
flow.
3. Provides frequent small VT in HZ
Pressure Monitoring System
1. Safety and alarms rely on this system
2. The PMS senses pressures within the
patient’s circuit through the tubing that
runs from the y-coupler
Electronic Power Supply
Monitors:
1. Alarms
2. Pressures
3. Function of the oscillator
18
• 3100 A
13-14
8
4
3
11
5
9
7
6
10
12
15b
16
15a
17
2
1
3100A Interface:
1. Bias flow knob
2. Mean Pressure adjustment
3. Mean Pressure Limit
4. Power
5. % Inspiratory Time
6. Frequency
7. Start/Stop
8. Mean Airway Pressure
9. Set Max Paw
10. Set Min Paw
11. Paw >50 cm H2O
12. Paw <20 cm H2O
13. Power failure Button
14. Reset
15a Battery Low
15b Source Gas Low
16. Oscillator Overheated
17. Oscillator stopped
18. 45 second Silence
Adjustable Parameters
Amplitude:
Determines the volume of gas generated
by each frequency wave
IT%
Inspiratory Time Percentage
 33% IT = 22 milliseconds a 15 Hz
Amplitudes
 2.5 for
 3.0 for
 4.0 for
 5.0 for
 6.0 for
 7.0 for
Weight: kg/mg
<2.0 kg.
<3.0 kg
<2.5-4.0 kg
4.0-5.0 kg
< 10 kg
>20 kg
I:E: For HFOV
I:E also determines the time for
movement of the piston to generate
another oscillatory breath.
 Initial I:E of 1:2 for 3-15 Hz at 33%
IT
Oscillation/ Frequency (Hz)
Frequency = The Rate




15 Hz =900 BPM for neonates
12-14 Hz =600 BPM for termed infants
8 Hz =480 BPM for children 6-10 kg
6 Hz =360 BPM for children above 10 kg
MAP/PEEP:
Maintains constant distending
pressure in the airway
 15-18 cmH2O
PULMONARY DISEASES
AND DISORDERS TREATED
WITH HFOV
https://www.youtube.com/watch?v=dHuXtoODHuA
Pneumopertioneum
Sub cu-emphysema
Pneumomediastinum
Pneumothorax
Pneumopercardium
ARDS
Potential Advantages of HFOV are
1. Uniform inflation of the lung
fields
2. Improves gas exchange
3. Improves lung mechanics
4. Enables stable lung inflation
o Allows recruitment of alveolar
space
o Reduces the risk of volutrauma
o Reduces risk of high peak airway
pressure (PIP)
o Reduces the risk of airway
stretching
o Improves V/Q matching
5. Reduces air leak
6. Decreases the amount of
inflammatory mediators and
alveolar edema
7. Prevents the development of
hyaline membrane disease (HMD)
CMV VS HFOV
During CMV, there are swings between the zones of injury
from inspiration to expiration.
During HFOV, the entire cycle operates in the “safe
window” and avoids the injury zones.
INJURY
HFOV
CMV
INJURY
HFOV is used to prevent Ventilator Induced Lung Injury
Zone of Overdistention
Volume
Safe
window
Zone of
Derecruitment
and
atelectasis
Goal is to avoid injury zones
and operate in the safe window
Pressure
Indications:
• When traditional ventilation fails
• Airleak syndromes
• For patients with severely low lung compliance
• Refractory hypoxemia
Contraindications:
• ICP
• obstructive lung disease
• increased airway resistance (small endotracheal tube)
• asthma
• secretions
• increased physiological dead space
Work Citations Page:
Alves, Amanda. “High Frequency Oscillatory Ventilation HFOV; a new strategy in the
Treatment of patients with Acute Respiratory Distress Syndrome and low lung compliance.”
CIMC 2000. Web 13 August 2014.
Birch, Pita. “Newborn Services Clinical Guideline High Frequency Oscillatory Ventilation.”
Web. 14 August 2014. http://www.adhb.govt.nz/newborn/guidelines/respiratory/hfov/hfov.htm
CareFusion; “3100A High frequency oscillatory ventilation; Operator’s manual.” CareFusion
Corporation. 222745 Savi Ranch Parkway Yorba Linda, CA 92887-4668. Web 18 August 2014
Haines, Mike. “Mechanical Ventilation: High Frequency Ventilation.” Respiratory Therapy
Files. http://www.respiratorytherapyfiles.net Web. 8 August 2014.
Jeng, Mei-Jy. Lee, Chen, Soong. “Neonatal air leak syndrome and the role of high-frequency
ventilation.” Sci Verse Science Direct Journal of the Chinese Medical Association 75 (2012)
551e559 Web. 8 August 2014. http://homepage.vghtpe.gov.tw/~jcma/75/11/551.pdf
Prost, Allen. “High Frequency Oscillation Ventillation.avi.” Youtube.com. 2011.
Web 24 Aug. 2014.
Slee-Wijffels1, Fieke YAM. RM van der Vaart, Twisk, Markhorst, Plötz5 “High-frequency
oscillatory ventilation in children: a single-center experience of 53 cases, pp. R274” Open
Access. 16 Web August 2104. http://www.biomedcentral.com/content/pdf/cc3520.pdf
Slee-Wijffels1, Fieke YAM. RM van der Vaart, Twisk, Markhorst, Plötz5 “High-frequency
oscillatory ventilation in children: a single-center experience of 53 cases, pp. R274” Open
Access. 16 Web August 2104. http://www.biomedcentral.com/content/pdf/cc3520.pdf

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