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High Frequency Ventilation

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Megan Spurny

on 19 April 2013

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Transcript of High Frequency Ventilation

An Intro to High Frequency Ventilation
M. Spurny MHS, RRT MV using Tv < Vd @ supraphysiologic rates
Rates > 150bpm
Usually rate = hertz (Hz)
1Hz= 60 breaths/min What is it? Link between MV, O2 and CLD shortly after intro to CMV
High Vt contributes to further damage in pts. with areas of low compliance:
Infants: Surfactant inactivation/deficiency
LaPlace's Law= Healthy areas receive bulk of flow or pressure causing damage
Large delta P's with CMV cause stretch injury Why is it? Release of inflammatory mediators/scarring/CLD Developed to mimic a dog panting to increase alveolar ventilation
Increased diffusion in the large and medium airways alters gas flow
Bulk convective flow
Pendelluft phenomenon
Taylor dispersion
Brownian movement
Collateral ventilation
Complete opposite on ventilatory spectrum from CMV How does it work? Form of gas mixing between adjacent alveoli with different time constants
"Air Swing"
Creates some equilibration of gas in alveoli
Difference in compliance between alveoli has a larger impact on pendelluft flow than does a difference in resistance between alveoli Pendelluft Convection: The concerted, collective movement of ensembles of molecules
Large amount of flow and gas mixing in airways due to high frequencies and flow rates
Helps ventilate the proximal airways and aide in larger amount of diffusion Bulk convective flow Contributes to total gas transport due to longitudinal dispersion of gas in a diffusive process
Amplified by radial transport and laminar flow in small airways
'Pushes' Small Vt's forward towards alveoli Taylor Dispersion Responsible for gas particle interchange
Contributes to diffusion of gases in respiratory tract
HFOV- Virtually no gas flow in alveoli due to attenuation, Taylor dispersion and high total cross sectional ares
Principle means of gas diffusion and gas transport is a product of Fick's Law Brownian Movement Allows for air movement accross alveolar units
Via the pores of Kohn and canals of lambert OR the inequality of time constants Collateral Ventilation High Frequency Conventional and Positive Pressure
High Frequency Flow Interruption
High Frequency Jet Ventilation
High Frequency Oscillatory Ventilation Types of HFV Modification of CMV pressure limited ventilation
RR up to 150bpm
Tend to deliver high Vt
Possibility for gas trapping
Not FDA approved (generally not used) for use in neonates HFPPV: Pressure regulated
Low Vt, short duration
In conjunction with CMV
ETT attenuates intratracheal and intrapulmonary pressures
Passive exhalation or assisted
Basically similar to high frequency jet concept HFFI's Short pulsed jets @ ETT
Vt is combo of jet breath and entrainment vols. that are dragged along with each jet
Jet ventilator used with CMV Always
Passive exhalation
Baseline pressures are provided by CMV HFJV Extremely small Vt and High rates
Continuous distending pressure (MAP)
Uses a driving piston to drive flow
Outward flow of expiratory gases is enhanced by ACTIVE exhalation HFOV Use standard ETT
Allow precise control over MAP
Allow precise control over amplitude

These things allow precise control over:
Oxygenation

Ventilation What's the same? MAP, FiO2 Delta P, Frequency Some are used in conjunction with CMV
Oscillator uses ACTIVE exhalation
It's opposite day for frequency:
Increase Ventilation: Decrease frequency
MAP is NOT PEEP What's Unique? Data primarily for neonates:
Diffuse, homogenous lung disease (or lung prone to ATX)
CMV is failing or may cause further damage
Surfactant deficiency (RDS)
Diffuse PNA
Existing pulmonary air leak syndromes
PTX
PIE Indications: Acute RDS
Pulmonary Air Leak
Rescue therapy for failure of CMV**
?? Cardiac repair surgeries Pediatric Indications: ** The term 'rescue' should be considered carefully... Always be proactive with therapies, not reactive Frequency:
Rare to go <4hz or >15hz
Less impact on ventilation than Delta P
Smaller kids= higer hz
Larger kids= lower hz
START: 10hz
Amplitude/PIP:
Delta P= Tv
Chest wiggle
Dependent on pulmonary mechanics
Non-invasive monitoring/ABG's Settings: Settings: MAP:
Continuous distending pressure- not PEEP
Controlled by bias flow and expiratory valve aperture
Creates a static lung volume (almost no flow in alveoli)
Optimizes lung volumes
2-3cmH2O > MAP on CMV
12-20cmH2O if new start (Depending on diagnosis, SpO2, hemodynamics)
PEEP:
Start at CMV level
Increase as you would on CMV
Maintain MAP
If on HFJV, if increasing PEEP, consider Increasing PIP Flow:
Adequate enough to facilitate MAP and to ensure pt. not outdrawing flow
Variable with device
Inspiratory Time:
HFJV: Defined by jet-on time (milliseconds, usually 0.020)
HFOV: 33% (it's a % of total cycle time. Creates 1:2 IE ratio
Discourages severe air trapping Settings: High Volume Strategy:
ATX prone lung
Optimize lung inflation to maintain V/Q
Reduce shearing forces due to high Vt's
Methods:
Increase MAP in small increments (1-2cmH2O) until oxygenation improves or MLV is reached
Watch for impairment of venous return (decrease in CO)
OR
Sustained inflations
Applying Pplat pressures> than alveolar opening pressures for periods of 5-30 Seconds (Also called recruitment maneuvers)
MAP between inflations should be slightly less than MAP with other method
Results may depend on lung physiology
BIG risk of air leak Management: Low Volume Strategy:
Air leak syndromes
Difficult to achieve MLV
Slowly allow lung to deflate or minimize air leakage
Usually have to accept higher FiO2
Utilize a lower MAP
Decrease Tv
Tolerate hypercarbia and moderate acidosis Management: Decrease amplitude to maintain CO2 criteria
Wean FiO2 <40%
Decrease MAP as tolerated by SpO2, FiO2, CXR
1-2cmH2O Q 2-3 hours
Evaluate need for CMV or extubation to CPAP, SiPAP or O2

P. 365 Table 20.2 Illustrates setting manipulation Weaning: Breath Type Distinction What are the most noticeable differences between breath types? Optimal Distention How is Ve manipulated with HFOV? What should oxygenation look like?


What should ventilation look like? CMV versus HFOV Inspiratory/Expiratory Patterns How does this even work?
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