High Frequency Ventilation Flashcards
What Is High Frequency Ventilation (HFV)
A form of mechanical ventilation that uses frequencies that are greater than 150 bpm and small tidal volume
Often the tidal volumes will be smaller than deadspace
Deadspace estimated to be 2.2 mg
Frequencies in HFV
Frequencies is specified in Hertz (Hz) which is cycles per second
1 Hz=1 cycle/sec=1 breath per second=60 bpm
What Are the Indications for HFV
Acute Lung Injury (Severe Oxygenation Failure)
Ventilation failure
Upper airway surgery and bronchoscopy
BP Fistula or pulmonary air leaks in neonates (eg. PIE)
Indications for HFV-Acute Lung Injury
- Adult: No evidence that HFV is better than conventional CHR P&P
- When OI >20 on two ABG that are 6h apart
- Neonates:HFV is considered superior to conventional ventilation, however when surfactant lung protective strategies and NO is used there does not seem to be a benefit to HFV over conventional
Indications for HFV-Ventilation Failure
Ph <7.25 with Vt <6 mL/kg and plateu pressure <30 cmH2O
Indications for HFV-Upper Airway Surgery and Bronchoscopy
HFJV preferred over conventional ventilation as they provide more efficient gas exchange with an open airway
Indications for HFV-BP Fistula or pulmonary air leaks in neonates (eg. PIE)
HFJV is most used traditionally (less bulk flow= less movement)
Air leak disease is usually the result of barotrauma where as volutrauma tends to form a ARDS picture
High Frequency Positive Pressure Ventilation (HFPPV)
Modified form of conventional ventilation
Uses a conventional ventilator high a high RR (120-240 bpm) and a low Vt (3-5 ml/kg)
Used before HFJV/HFO were readily available to be used so it is not used much now
High Frequency Flow Interrupter (HFFI)
Uses a ball that moves at a set frequency to interrupt the flow to the patient
High Frequency Percussive Ventilation (HFPV)
Combines HFV and conventional ventilation
Superimposes oscillations on the conventional ventilation
The percussive vibrations are thought to aid in secretion mobilization.
High Frequency Jet Ventilation (HFJV)
Passive exhalation
When expiration is passive there is the risk of breath stacking
Combines the use of a jet ventilator and a conventional ventilator
The conventional vent provides the PEEP (which = MAP) and +/- sigh breaths
The jet vent pulses above this
High Frequency Oscillation (HFO)
Most commonly used
Only type of HFV that uses active exhalation
Active Exhalation
High Frequency Jet Ventilation (HFJV) Methods of Administration
Using a specially designed ETT (eg. Hi-Lo Jet ETT)
Using a specially designed ETT connector (no re-intubation required) and the Jet Ventilator in addition to the conventional vent
Via a trans-tracheal catheter
A crude form; usually present in difficult airway carts
How Does HFJV Work
Uses 14-18 gauge small bore injector in which gas is introduced at high pressure (15-50 psi). Gas leaves from a different route. Gas flow interrupted by pneumatic, fluidic or electronically controlled solenoid valves.
Jet Ventilation ETT
Central Lumen for the conventional ventilator
Pressure monitor which opens below the cuff
Another lumen which delivers the jet ventilation and open above the cuff
High Frquency Osillation Main Controls
FiO2
MAP
Amplitude
Frequency
TI% or I:E
Bias Flow
Indications in Neonates for HFJV
- A HFJV for infants
- Indications for use:
- RDS
- Rescue infants with lung injury e.g. PIE
- Others:
- Air leak for reasons other than PIE
- Meconium aspiration
- Pneumonia
- CDH
- PPHN
Basic Theory of Jet Ventilation
VT ~ 1 ml/kg = half the size of anatomic dead space
High velocity inspiration – moves through deadspace gas instead of pushing dead space ahead of fresh gas
Exhaled gas cycles out in a counter-current helical flow pattern around incoming gas which helps with clearance of secretions from the airway
PIP settings may compare to conventional but inspirations are short and fast therefore pressure falls quickly meaning alveolar pressures much lower than peak airway pressure
Bunnell LifePulse
Jet Ventilation
How does the conventional ventilator work with jet ventilation
The conventional ventilator is responsible for
Background conventional ventilation
Entrainment of gas
Maintenance of PEEP
HFJV-Ventilation
Amplitude produces VT and controls PaCO2
Frequency (in Hz)
Exhalation is passive; PEEP is constant if rate low enough to prevent air trapping
NOTE: when Ti is constant changes in the frequency do not impact VT (and thus, an increased rate will decrease PaCO2)
HFJV-Oxygenation
FiO2 (on the conv. vent)
PEEP = MAP
PEEP is the primary controller for MAP and oxygenation
Find optimal MAP by raising PEEP 1-2 cmH2O above conventional settings – stablize patient using CMV of 5bpm and FiO2 getting stable SaO2 and then switching to CPAP
High Frquency Osillation How It Works
Requires specialized machines to provide HFO
Basically uses a bias flow past the airway and either a piston, high frequency speaker (diaphragm) or rotating valve to provide the oscillations
High Frquency Osillation How It Differs from other HFV Techniques
Expiration is active
Gas flow is sinusoidal
Means it flow in and out in a repeatable manner
Bulk flow rather than jet pulsations are delivered
Minute Ventilation Equation in HFOV
ṾE = f x VT2VT: 0.8 to 2.0 ml/kg (less than deadspace!!)
Still results in effective CO2 elimination due to the gas transport mechanisms involved in HFV
The tidal volume is the bigger factor in the MV!
Proposed Mechanisms of Gas Exchange
Bulk Convection
2.Pendelluft gas movement
Gas moving from one lung unit to another due to differences in R and C
3.Asymmetric velocity profiles (Streaming)
Gas in the center moves faster than gas at periphery
Also bi-directional gas movement (at the center O2 moves into the lungs while at the periphery CO2 moves out)
4.Taylor dispersion
High velocity gas movement enhances the development of turbulence in the conducting airways
This movement encourages dispersion of gas, both laterally and centrally
5.Cardiogenic oscillation
The oscillations of the circulatory system assist gas movement, especially at high frequencies
3100: Theory of Operation
HFOV Oxygenation
- The MAP is used to inflate the lung and optimize the alveolar surface area for gas exchange
- MAP = Lung Volume (FRC)
- Controls Affecting Oxygenation are:
- FiO2
- MAP
- (TI%)
Alveolar Ventilation in HFV and CV
Alveolar ventilation during conventional ventilation is defined as: f x VT
Alveolar ventilation during HFV is defined as: f x VT2
Therefore, changes in volume delivery have the most significant affect on CO2 elimination in HFV
HFV and Ventilation
CO2 removal is affected by 3 main controls:
Frequency (Hz): DecreaseFrequency s volume (and MV!!)
Amplitude (Delta P): Amplitude s volume
(TI%): Insp. Time s volume
When you are adjusting for CO2 consider changing your amplitude first in babies and for adulst you should consider changing the freuqncy first
What are same less common ways to remove CO2 with HFV
Max bias flow, deflate cuff.
HFOV and Frequency
to decrease PaCO2 you would decrease frequency!! This allows for a larger VT which is the bigger part of the MV=f x VT2
Frequency controls the time allowed (distance) for the piston to move. Therefore, the lower the frequency , the farther the piston moves and the greater the volume displaced. The higher the frequency , the less distance the piston travels and the smaller the volume displaced.
What is your first and second choice in HFOV for Decrease PaCO2
1) Frequency
2) Amplitude which is produced by the power setting
Note: As the MAP is increased there is less DP available, B/c the higher the MAP the more resistance the piston has to work against.
% Inspiratory Time Effect on CO2
▪Effect on CO2:
▪Increased % Insp Time allows more time for piston movement and \ can assist with CO2elimination
▪Effect on O2:
▪Increased % Insp Time increases delivered MAP \ can improve oxygenation
3100: Piston Centering
3100B: Piston Centering is automatically regulated by the instrument and requires no operator intervention.
3100A: This is adjusted by the operator!
3100: Starting Up
To pressurize the patient circuit, the Reset / Power Fail button must be pressed and helduntil the mean airway pressure builds up and then
The Start / Stop button is used to start and stop the oscillator.
The oscillator may be stopped without a complete loss of mean airway pressure.
3100: Preset Alarms
Upon activation the oscillator will stop, the dump valve opens and the circuit vents to ambient
Bias flow is still delivered when the MAP<5 cmH2O is activated.
3100: Source Gas Low
The source gas low alarm will provide only a visual indicator if either of the high pressure gas supplying the blender falls below 30 psig OR if the source gas feeding the piston cooling system falls below 30 psig.
3100: Battery Low
The battery low alarm will provide only a visual indicator when the nine volt alarm battery needs replacement
This battery is used to power the Power Fail alarm NOTthe oscillator.
3100: Oscillator Overheated
Failure to correct the situation will result in piston failure!
The oscillator overheated alarm will provide only a visual indicator if the linear motor temperature exceeds 150°C
Under N operating conditions and with a dedicated air line to cool piston this should not occur.
3100: Oscillator Stopped
The oscillator stopped alarm will provide audible and visual indicators if the oscillatory amplitude is at or below 7 cmH2O and the oscillatory subsystem is energized.
(as indicated by the illumination of the green LED on the start stop button)
Adjusting the Parameters of HFOV in Adults
Oxygenation
FiO2is primary control to adjust, if at 100% then increase Paw by 3-5 cmH2O
Wean Paw by 1-2 cmH2O Q4H until at 34 cmH2O; then wean FiO2
Adjusting the Parameters of HFOV in Adults
Ventilation
▪Frequency is the primary control to adjust (increments of 1 Hz)
▪Goal ΔP is 90 cmH2O
▪Consider increasing bias flow up to 60 LPM
▪Consider inducing a slight ETT cuff leak
When Making Changes
The controls can alter more than one parameter (indirectly) always double checkthat all other settings remained the same changes (and adjust if necessary)
. As MAP is increased the amplitude will decrease (for the same power setting)
HFOV Returning to Conventional Ventilation
Patient stable for more than 12h withFIO2£0.40 and Paw £25 cmH2O
Patient tolerating (or at least recovering quickly from) interventions without prolonged desaturation events
Typical Initial Settings (Neonate)
Bias Flow
Bias Flow = 12-15 LPM
Typical Initial Settings (Neonate)
Frequency
Frequency = 8-15 Hz
Based on weight…smaller the baby the higher the Hz and vice versa
Higher frequencies used for air leak syndromes
Typical Initial Settings (Neonate)
FIO2
FIO2= set 20% higher than current mechanical ventilation settings (may need to start at 100%)
Typical Initial Settings (Neonate)
Power
Power = ΔP=~20 cmH2O to start= adjust to achieve appropriate wiggle
When weaning don’t typically go below a ΔP of 16 cmH2O)
Typical Initial Settings (Neonate)
Paw
Paw = initially set 2 cmH2O > Paw on conventional vent
Lower Paw for air leak syndromes
Typical Initial Settings (Neonate)
% I Time
% I Time = 33%
◦FIO2= set 20% higher than current mechanical ventilation settings (may need to start at 100%)
◦Paw = initially set 2 cmH2O > Paw on conventional vent
▪Lower Paw for air leak syndromes
◦Power = ΔP=~20 cmH2O to start= adjust to achieve appropriate wiggle
When weaning don’t typically go below a ΔP of 16 cmH2O)
In Neonates (AHS) the primary controls for oxygenation and ventilation
Ventilation = ΔP (then f)
Oxygenation = MAP (then FiO2)
HFOV Starting Up
The circuit must first be occluded and then pressurized to above the preset min MAP alarm before oscillations can begin
Ideally the ETT is clamped at end-inspiration on the conventional vent, the oscillator is connected, the circuit is pressurized (hold Reset/Power Failure), the clamp is released, then the Start/Stop button pressed to begin oscillations
This minimizes de-recruitment of the lung!
Always leave the conventional ventilator at the bedside and set up appropriately for the patient!
HFOV Lung Inflation and Recruitment
Monitored at least daily via CXR
Adult: Should see posterior 9 to 11 thribs in both hemithoracesas an indicator of overallideal lung recruitment
Catheter-if tip left within circuit will dampen the effective delta P in lungs
LRM within 5-10 minutes of initiation (adults)
Disconnections
All efforts should be made to avoid disconnecting the patient
Eg.Use closed suction systems (*a note on these: ensure catheter tip fully removed!)
LRM should be performed after any disconnect – Adult
HFOV Wiggle
This wiggle is the only indication that the airway is patent and ventilation is reaching the lungs
An RN/RT should always be at the bedside
If the wiggle diminishes or is absent this is indicative of a partial/full airway obstruction!
The oscillator Will Not Alarm in the Event of an Airway Obstruction!
This wiggle action may cause the ETT to be wiggled out!
Repositioning/re-securing of the airway needs to be done often
Oscillator Circuits
These are made of a low compliance material to minimize the compressible volume of the circuit
◦Heated humidity always used
▪Use auto-fill pots to maintain constant compressible volume and temperatures
▪Due the high levels of bias flow through the circuit the water is used quickly!
▪Pressure bags around the water used to prevent inflation of bag
◦There is a water trap positioned below the diaphragm
Always leave a small amount of water in to act as a seal
Oscillator Circuits and HME
Can not use HME B/C VT’s are < VDHME’s are ineffective
