Oscar Hfovtheory

8/13/2019 Oscar Hfovtheory

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High FrequencyHigh Frequency

Oscillatory VentilationOscillatory Ventilation

Dr George Findlay

Consultant Intensivist

University Hospital of Wales

Cardiff


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Risk factors in ARDS:Risk factors in ARDS:

Trauma

Shock Syndromes (Sepsis,Cardiogenic)

Gastric Aspiration Burns

Diffuse Pneumonias

Near Drowning

Metabolic Events (Pancreatitis, Uremia)

Drug Overdose Systemic Mediator Release associated Diseases

-Transfusion Reaction

- Disseminated Intravascular Coagulopathy- Cardiopulmonary Bypass


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Absence of Surfactant

Tidal Breathing

High Distending Pressures

Airway Stretch / Distortion

Cellular Membrane Disruption

Edema / Hyaline Membrane Formation

Higher FIO2 / Pressures

Barotrauma, PIE, BPD

PulmonaryInjury

Sequence


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Pulmonary Injury Sequence:Pulmonary Injury Sequence:

Endo/Epithelial Damage Alveolar Cell Injury and/or loss

Capillary Congestion

Interstitial/Alveolar Edema, Hemorrhage Protein Accummulation

Surfactant Deactivation

Atelactasis

Hyaline Membrane Formation

Inflammatory Cell Migration

Volutrauma , Stretch forces

Increased Protein Leak, Atelectasis


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Respiratory Therapy Concepts in ARDS :Respiratory Therapy Concepts in ARDS :

Conventional Ventilation :

- PEEP, Fi02- Inverse Ratio

- Low Volume Pressure Limited Ventilation

- Prone positioning

- Perm. Hypercapnia

- NO Inhalation

- LFPPV + ECCO 2R

- Partial Liquid Ventilation

Conventional Ventilation + HFJV

HFOV


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NIH ARDS Network USANIH ARDS Network USA Patients : 850 P/F ratio < 300 (79 %


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Changing Lung Volume in CV:Changing Lung Volume in CV:

Paw = Lung Volume !


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Necessity to achieve gas exchange but

eliminate tidal breathing

Use of mean airway pressure sufficient enough tomaintain a constant intrapulmonary pressure aboveclosing pressure, and eliminate the bi-phasic pressure

swing, will alter the development of the pulmonaryinjury

Meredith K, et al , 1989 - baboons

Jackson C, et al, 1990 - ring tail monkeys

De Lemos, et al, 1992 - baboons


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HFOV:

Produces a moreuniform ventilation

pattern Maintains normal

architecture of the

lungs duringventilation.

CMV lung biopsy

HFOV lung biopsy

Meredith et al

24 h

24 h


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If we cannot prevent the injury sequence , then the

target goal is to interrupt the sequence of events !

High Frequency Oscillation does not reverse injury,

but will interrupt the progression of injury


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Optimized Lung Volume strategy:Optimized Lung Volume strategy:

1.) Increase Lung Volume above critical opening pressure to the

Optimum and keep it there in Inspiration and Expiration !

Benefits: - homogenous gas distribution

- reduced regional atelectasis- maximized gas exchange area and pulmonary blood flow

- better matching of ventilation/perfusion

- reduction of intrapulmonary shunting- reduced Oxygen exposure


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HFOV Principle:HFOV Principle:

ET Tube

BIAS Flow

Patient

CDP

Adjust Valve

Oscillator

Increase FRC with a super CPAP system


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Mean Airway pressure 5 cm H2O

Optimized Lung Volume Strategy:Optimized Lung Volume Strategy:

CT Scan :ARDS pig model 30 kg


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Mean Airway pressure 25 cm H2O




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Mean Airway Pressure 40 cm H2O




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CDP= FRC

CT 1 CT 2

CT 3

Paw = CDPContinuous

Distending

Pressure


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2.) Decrease Tidal Volumes to less or equal then dead space

and increase frequency !

Benefits: - no excessive volume swings

- reduced regional overinflation and stretching

- reduced Volutrauma


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GAS EXCHANGE IN HFOV:GAS EXCHANGE IN HFOV:

1.) Convection (Bulk Flow) Ventilation

2.) Asymetrical Velocity Profile

3.) Taylor Dispersion4.) Molecular Diffusion

5.) Pendelluft

6.) Cardiogenic Mixing


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SUGGESTED READING:SUGGESTED READING:

Chang HK. Mechanisms of gas transportduring ventilation by HFOV, Brief Review,

J Appl Physiol, 1984

Schindler M, et al. Effect of Lung

Mechanics on Gas Transport During HFO.Pediatric Pulmonology, 1991


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ET Tube

BIAS Flow

Patient

CDP

Adjust Valve

Oscillator

Decrease TVs to physiological dead space and increase frequency


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CDP=FRC=Oxygenation

+ + + + +

- - - - -

Amplitude

Delta P =Tv =

Ventilation

I

E

HFOV = CPAP with a wiggle !


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Pressure transmission CMV / HFOV :Pressure transmission CMV / HFOV :

Distal amplitude

measurements with

alveolar capsules in

animals, demonstrate itto be greatly reduced or

attenuated as the

pressure traversesthrough the airways.

Due to the attenuation

of the pressure wave, bythe time it reaches the

alveolar region, it is

reduced down to .1 - 5cmH2O.

Gerstman et. al


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Pressure transmission HFOV :Pressure transmission HFOV :

P

T

proximal

trachea

alveoli


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Pressure curves CMV / HFOVPressure curves CMV / HFOV


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Pressure (Amplitude) Controls CO2CDP (Paw) Controls O2


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HFOV effectively decouples:HFOV effectively decouples:

Oxygenation & VentilationOxygenation & Ventilation

Diff b t CV d HFOV


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Differences CV HFOV

Rates 0 - 150 180- 900

Tidal Volume 4 - 15 ml/kg 0.1 - 5 ml/kg

Alv Press swing 0 - > 50 cmH2O 0.1 - 5 cmH2O

End Exp Vol Low-normal High-normal

Gas Flow Low High

Differences between CV and HFOV


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High Frequency VentilationHigh Frequency Ventilation

Definition:Definition:

All rates above 150 breaths per minute(FDA)

Twice resting rate and tidal volume equal orless then anatomical dead space

(Ackermann)

Greater then four times natural breathing frequency

(Slutsky)


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High Frequency Ventilation in Adults:High Frequency Ventilation in Adults:

HFJV : High Frequency Jet Ventilation

HFOV : High Frequency Oscillating Ventilation


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HV Jet Ventilator in ARDS:HV Jet Ventilator in ARDS:

Delivers short pulses of pressurized gas in ET tube

Advantages:

- Simple devices

- Improvement of gas exchange

Disadvantages

- Need for combination CV/HFJV

- Need for cannula / modified ET tube

- Passive exhalation- Air trapping / Airway stretch

- Humidification problems


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HFOVHFOV--HFJV what is different ?HFJV what is different ?

Mechanism

Frequency

Exhalation

CDP Control

Humidity

ET Tube

HFOV HFJV

Oscillator Jet, Set back Jet

3-15 HZ(180-900)

1-10 HZ(60-600)

Direct setting Gas trappingby

incr. Frequency andset Peep

Active Passive

Standard

Humidifier

Vaporizer, Nebulizer

Humidity Entrainment

Standard ETT Modified ETT


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3100 B HFOV Resume:3100 B HFOV Resume:

Less Oxygen exposure:

Stable lung inflation

Recruitment of alveolar space Improved matching V/Q

Reduction of Volutrauma:

No conventional breaths needed Less Volume swings No high peak pressures

Active Exhalation

Reduces Airtrapping

Reduces Airway stretch

Sufficient Humidification less risk NTB

HFOV effectively

decouples

Oxygenationand

Ventilation


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31OO B HFOV31OO B HFOVInstrument ControlsInstrument Controls

BIAS Flow ( Continuous Flow ) Continuous Distending Pressure (CDP)

Delta Pressure Oscillating Frequency

Inspiratory / Expiratory Ratio


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( 3100 B settings !)

HFOV:

3100 B


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SensorMedics 3100B

Electrically powered,

electronically controlled

piston-diaphragm oscillator

Paw of 3 - 55 cmH2O

Pressure Amplitude from 8 -

130 cmH2O Frequency of 3 - 15 Hz

% Inspiratory Time 30% -

50% Flow rates from 0 - 70 LPM


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31OO B HFOV31OO B HFOVInstrument ControlsInstrument Controls

BIAS Flow ( Continuous Flow ) Continuous Distending Pressure (CDP)

Delta Pressure

Oscillating Frequency

Inspiratory / Expiratory Ratio


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Paw is created by a continuous bias flow of gas past the

resistance (inflation) of the balloon on the mean airway


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resistance (inflation) of the balloon on the mean airway

pressure control valve.

OxygenationOxygenation


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OxygenationOxygenation

The Paw is used to

inflate the lung and

optimize the

alveolar surface

area for gas

exchange.

Paw = Lung

Volume


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Bias Flow

CDP Control Balloon

Red Line Balloon Control


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Balloon Deflation:(valve opening)

-

- main power failure

- Map > 60 cm H2O- Map < 5 cm H2O

Oscillator Section


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Controls: Frequency (3-15 Hz) Inspiration time (30-50%)

pressure (0 - > 130 cm H2O)

Start/Stop Button

Centering display shows movement of the piston (not position of the piston ! Centering of the piston is connected to I-time (automatically!)


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Primary control of CO2

is by the stroke volume produced

by the Power Setting.


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Alveolar ventilation during CMV is defined

as:

F x VtAlveolar Ventilation during HFV is defined

as:

F x Vt 2

Therefore, changes in volume delivery (as afunction of Delta-P, Freq., or % Insp. Time)

have the most significant affect on CO2

elimination

Ventilation


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Ventilation

Secondary control of PaCO2 is the Frequency set.


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Frequency controls the time allowed

(distance) for the piston to move.Therefore, the lower the frequency ,

the greater the volume displaced,

and the higher the frequency , thesmaller the volume displaced.

R l ti D lt P d O ill tiR l ti D lt P d O ill ti


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Relation Delta Pressure and OscillatingRelation Delta Pressure and Oscillating

FrequencyFrequency

Power control adjusts Oscil lator movement (forward/backward)

Oscillator movement creates Delta Pressure Delta Pressure controls TV

Oscillating Frequency effects TV

( TV )2 * Frequency = VCO2 Delta P controls Ventilation, Frequency effects Ventilation

Delta P adjustable : > 130 cm H2O

Frequency adjustable: 3 - 15 Hertz ( HZ = times per second )

InspiratoryInspiratory / Expiratory Ratio:/ Expiratory Ratio:


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InspiratoryInspiratory / Expiratory Ratio:/ Expiratory Ratio:

I/E Ratio adjustable with Inspiratory time control Inspiratory time = Forward movement piston

Expiratory time = Backward movement piston

Backward movement piston = active exhalation ! Recommended Insp. time = 33% (prevents airtrapping)

++

----

30%

70%

Inspiratory time adjustable: 30% - 50%

CO2 removal Block v.s. Sine waveCO2 removal Block v.s. Sine wave


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SineBlock Block

PCO2

55 Kg lung lavaged pigDp 60 CDP 20 FiO2 0.3

Alarm Section

( CDP / MAP )


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( CDP / MAP )

Alarm Settings:

Visual Indicators:

Alarm Silence Button:

Reset Button:

- maximum CDP (MAP)

- minimum CDP (MAP)

- source gas low- battery low

- oscillator overheated

- oscillator stopped

- 45 sec. suppression

- controls Red line balloon


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Pressure Controls CO2MAP/ CDP Controls O2


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Differences 3100A/3100B:Differences 3100A/3100B:3100 A:

0 - 40 l/min

3 - 45 cmH2O

>90 cmH2Omax. prox. Amplitude

CDP > 50 cmH2O

CDP < 20% max.CDP alarm setting

3100 B:

0 - 60 l/min

7 - 55 cmH2O

>130 cmH2Omax. prox. Amplitude

CDP > 60 cmH2O > 5sec

CDP < 5 cmH2O

Bias Flow:

CDP Adjust:

Delta P:

Red line

balloonvalve opening :

Piston centering

adjustable

Piston centering

connected toI/E Ratio

Minimum Bodyweight Limit 3100 B:Minimum Bodyweight Limit 3100 B:


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Red line balloon

valve opening

3100 A 3100 B

CDP > 50 cm H2O CDP > 60 cm H2O > 5 sec.

CDP < 20% Max. CDP < 5cm H2O

CDP alarm setting

Recommended Patient minimum Bodyweight Limit

for the use of the 3100 B is 35 KG !

Upper limits for valve opening in the 3100 B

can cause severe complications in infants and

pediatric patients below 35 KG bodyweight !

Patient Circuit CalibrationPatient Circuit Calibration


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Ventilator Performance CheckVentilator Performance Check


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