Transcript File - Respiratory Therapy Files

Introduction to
High Frequency Ventilation
Michael Haines, MPH, RRT-NPS, AE-C
Objectives
•
•
•
•
•
•
TYPES OF HFV
There are four basic types of HFV:
High frequency jet ventilation
High frequency oscillatory ventilation
High frequency percussive ventilation
High frequency positive pressure
ventilation (RARE normal vent with high
rates)
• INO with HFV
Introduction
• Respiratory insufficiency from ARDS remains a high risk
for mortality. Intensification of conventional ventilation
with higher rates and airway pressures leads to an
increased incidence of barotrauma. Especially the high
shearing forces resulting from large pressure amplitudes
damage lung tissue. Either ECMO or high-frequency
oscillatory ventilation might resolve such desperate
situations. Since HFOV was first described by
Lunkenheimer in the early seventies this method of
ventilation has been further developed and is now
applied the world over.
High Frequency Jet Ventilation
HFOV 3100 A –
Neonates/Peds
HFVO 3100 B- Adults
High frequency percussive ventilation
Introduction
• HFV is a type of ventilation that delivers small
tidal volumes (VT < VDS ) with supraphysiologic
respiratory rates >150 bpm
• The goal of HFV is to provide adequate
ventilation/oxygenation in the presence of
severe restrictive disease in order to
prevent/reduce the risk of conventional ventilator
induced lung injury
• HFV uses momentum rather than airway
• pressure to overcome lung compliance
Introduction
• High-frequency ventilation was first
introduced 30 years ago as a method for
reducing intrathoracic pressure during
thoracic and laryngeal surgery. Highfrequency oscillation was developed in the
1970's for the treatment of lung disease of
prematurity but is now used for acute
hypoxemic respiratory failure in all ages.
Introduction
• The key difference from CMV is the usage of
high rates and low tidal volumes. Because the
tidal volume is smaller than the dead space, the
gas transport during HFV cannot be explained
by bulk flow theory as in CMV.
• HFV is not uncommon in nature and in fact
occurs in:
– Humming birds
– Panting dogs
Introduction
• Traditional wisdom: VA = f (VT - VDS)
• Physiologic (effective) dead space can
become < anatomic dead space
»Animal studies of HFV: adequate ventilation
can be achieved with VT as low as 1 ml/kg
» Flow streaming reduces effective dead space only portions of the anatomic DS are used
» Fresh gas penetrates some alveoli
Introduction
• During conventional ventilation direct alveolar ventilation
accomplishes pulmonary gas exchange. According to the
classic concept of pulmonary ventilation the amount of gas
reaching the alveoli equals the applied tidal volume minus the
deadspace volume.
• At tidal volumes below the size of the anatomical deadspace
this model fails to explain gas exchange. Instead, considerable
mixing of fresh and exhaled gas in the airways and lungs is
believed to be the key to the success of HFV in ventilating the
lung at such very low tidal volumes.
Amplitude and Hertz
• Amplitude (Power) height of wave
• Hertz (frequency) how close each wave is
Hertz
• Top: Hertz set at 3
• Bottom: 1 breath in conventional
Indications for Neonatal HFV
•
•
•
•
•
•
•
•
•
RDS non responsive to conventional ventilation
Prophylactic use is severe prematurity
PIE
PPHN
PN
Increase in intra-abdominal pressure e.g. NEC
MAS
CDH
TEF
• HFV can be used as a prophylactic means of ventilation for
extremely small neonates, but usually it is used after conventional
ventilation has failed (Increased Paw, FIO2 demands, refractory
hypoxemia, failure to ventilate, over distention, air leaks…). HFV
may also be used in conjunction with NiO and ECMO therapy for
patients failing to oxygenate.
Indications for Adult HFV
• ARDS/ALI (only disease process that has
been currently studied for use)
• Possibly massive airleak and BP fistula
Indications for HFV
• Some criteria used are: PaCO2 >50 mmHg or
FiO2 requirement greater than 0.5 to maintain
PaO2 of 50 mmHg.
• Oxygen index (OI =FiO2 * MAP /PaO2) >35
• PaO2/FiO2 ratio of less than 300
• Infants receiving HFV should be monitored
continuously for their oxygenation and
ventilation. They may require extra intravenous
fluid to compensate the relative volume
depletion resulting from redistribution of blood
flow
Why we use HFV
• It is safer and more effective to use
smaller VT at higher PEEP (MAP)
compared to larger VT at lower PEEP
• HFV uses momentum rather than airway
pressure to overcome lung compliance
• Greatest benefit in diseases of poor lung
• compliance
• »Optimizing PEEP (MAP) during HFV is
• critical
Why we use HFV
• Indications
• Rescue: This is the most established role
for HFV
• Prophylactic: In animal experiments HFV
causes less lung injury than conventional
ventilation.
• Which do you think is better?
• Normal (A and B) and acutely injured lung (C
and D). Alveoli at peak inspiration (A) and end
expiration (B) in the normal lung are very stable
with little change in size during tidal ventilation
(dots). High positive inspiratory pressure (PIP)
and low PEEP injurious ventilation causes a
ventilator-induced lung injury resulting in
alveolar instability. Injured alveoli at peak
inspiration (C) are inflated (dots) and totally
collapse (arrows) end expiration (D),
demonstrating severe instability during tidal
ventilation.
• In vivo photomicrographs of subpleural
alveoli in the rat after lung injury by saline
lavage ventilated with either conventional
mechanical ventilation (CMV) or highfrequency oscillatory ventilation (HFOV)
using a 2.5-internal diameter tracheal
tube. With CMV, a group of alveoli are
seen inflated during inspiration (dots) but
collapse with expiration (arrows). Alveoli
are very stable with HFOV during
ventilation. The same alveolus is seen with
HFOV at inflation and exhalation (dots).
Pulmonary Interstitial Lung Disease
(PIE)
Bulk flow to non compliant airways and alveoli increase
distending pressure resulting in air leaks
ARDS
Air leaks from the over stretching of
non compliant alveoli can cause:
•
•
•
•
•
•
•
Subcutaneous emphysema
Pneumothorax
P.I.E.
Pneumomediastinum
Pneumo-pericardium
Pneumo-retroperitoneum
pneuomoperitoneum
HFV is a method of mechanical ventilation that employs supra-physiological
breathing rates and tidal volumes frequently less than dead space. Because
conventional ventilation relies on the production of large pressure changes to
induce mass flow of gas in and out of the lungs, it may be associated with
deleterious consequences of volume and pressure changes at alveolar
level. These include air leaks, such as PIE and pneumothorax, and bronchiolaralveolar injury leading to chronic lung disease.
How does HFV work?
• HFV enhances both bulk flow (convection) and
diffusion of respiratory gases
»Abundant fresh gas “washes out” expired gas from
the airways
»Decreased pCO2 at the gas exchange boundary
increases diffusion
• Linear relationship between ventilator rate
• and CO2 elimination is no longer valid
• »CV: CO2 = f x VT; HFV: CO2 = f x VT2
• »Changes in rate have less impact on gas
• exchange than similar changes made during CMV
Venegas and Fredberg: Crit Care Med 22 (suppl):S49, 1994
How does gas exchange occur with
HFV
• Direct ventilation of most proximal alveoli
units by bulk convection
• Direct Bulk Flow Some alveoli situated in
the proximal tracheobronchial tree receive
a direct flow of inspired air. This leads to
gas exchange by traditional mechanisms
of convective or bulk flow.
How does gas exchange occur
with HFV
• Pendalluft effect – asynchronous flow among
alveoli due to asymmetries in airflow impedance.
This causes gas to re-circulate among lung units
and improve gas exchange. In healthy and,
more so, in diseased lungs, the mechanics of air
flow vary among lung regions and units within
regions. Variation in regional airway resistance
and compliance cause some regions to fill and
empty more rapidly than others. Some gas may
flow between regions if these characteristics
vary among regions that are in close proximity.
• Turbulence in the large airways causing
enhanced gas mixing
How does gas exchange occur with
HFV
• Taylor dispersion – Turbulent eddies and
secondary swirling motions occur when
convective flow is superimposed on
diffusion. Some fresh gas may mix with
gas from alveoli, increasing the amount of
gas exchange that would occur from
simple bulk flow.
• Collateral ventilation through non-airway
connections between neighboring alveoli
How does gas exchange occur
with HFV
• Cardiogenic Mixing
• Mechanical agitation from the contracting
heart contributes to gas mixing, especially
in peripheral lung units in close proximity
to the heart.
• Molecular Diffusion
• As in other modes of ventilation, this
mechanism may play an important role in
mixing of air in the smallest bronchioles
and alveoli, near the alveolocapillary
membranes.
How does gas exchange occur
with HFV
• Asymmetric velocity – convective gas transport is
enhanced by asymmetry between inspiratory and
expiratory velocity profiles that occur at branch points in
the airways. The velocity profile of air moving through an
airway under laminar flow conditions is parabolic. Air
closest to the tracheobronchial wall has a lower velocity
than air in the center of the airway lumen. This parabolic
velocity profile is usually more pronounced during the
inspiratory phase of respiration because of differences in
flow rates. With repeated respiratory cycles, gas in the
center of the airway lumen advances further into the lung
while gas on the margin (close to the airway wall) moves
out toward the mouth
Gas transport during HFV
•
•
•
•
1. Direct bulk flow
2. Taylor dispersion
3. Pendeluft
4. Asymmetric
velocity
• 5. Cardiogenic mixing
• 6. Molecular diffusion
•
Chang, HK Mechanisms of gas transport during
ventilation by high frequency oscillation. ;-563
Oxygenation with HFV
• Oxygenation is determined by lung volume
(affected by MAP) and FiO2. It is important to
maintain adequate lung volume to prevent
atelectasis and to preserve surfactant function to
achieve adequate oxygenation.
• Adequate MAP should be used to recruit alveoli
and maintain lung volume above functional
residual capacity (FRC).
• In contrast to CMV, lung volume is maintained at
a relatively constant level during HFV.
Oxygenation with HFV
• The ventilation/perfusion matching would
improve as a result of alveolar recruitment
when lung volume increases. The near
constant lung volumes in HFV results in
better gas distribution and avoids the
development of regional atelectasis in less
compliant lung units, hence resulting in
better ventilation/perfusion matching.
Adjustments of Ventilatory Settings
During HFV
• PaCO2 is reduced mainly by increase in
HFV amplitude.
• Changing the HFV frequency may have
unpredictable effects on PaCO2
• Increasing the HFV frequency leads to a
decrease in delivered tidal volume, and
may result in an increase in PaCO2.
Types of HFV
• Three types of HFV ventilators are approved for
use in infants/adults in the United States, :
– High frequency oscillatory ventilator (HFOV)
– High frequency flow interrupter (HFFI)
– High frequency jet ventilator (HFJV).
• All forms of HFV have common
characteristics:
Respiratory rate >150 bpm
Tidal volume= 1-3 mL/kg
noncompliant ventilator circuits
HFOV
• HFOV employs either a piston or diaphragm to oscillate
a bias flow of gas to generate both positive and negative
pressure fluctuations termed as amplitude.
• The adjustable parameters include:
–
–
–
–
–
–
Power
IT%
Mean airway pressure (MAP)
Bias flow
Frequency (Hz)
Amplitude
• Frequency is usually fixed for a particular patient group.
• The recommended range is 10-15 Hz for premature
infants and 8-10 Hz for term infants, around 5 Hz for
adults
HFOV
• Characterized by high respiratory rates between 3.5 to
15 hertz (210 - 900 breaths per minute), where 1 Hz=1
breath per second.
• The rates used vary widely depending upon patient size,
age, and disease process. Typically the smaller the
patient the higher the Hz and vise versa.
• Pressure oscillates around the constant distending
pressure (equivalent to Mean Airway Pressure), which is
usually set slightly higher than the MAP on conventional
ventilation.
• Gas is pushed into the lung during inspiration, and then
pulled out during expiration (active exhalation).
HFOV
• HFOV generates very low tidal volumes
that are generally less than the dead
space of the lung (watch for atelectasis
and sudden drop in vital signs during
implementation).
• Tidal volume is dependent on
endotracheal tube size, power and
frequency.
HFOV
• Different mechanisms of gas transfer are believed to
come into play in HFOV compared to normal mechanical
ventilation.
• Often used in patients who have refractory hypoxemia
that cannot be corrected by normal mechanical
ventilation such as is the case in the following disease
processes: severe ARDS, ALI and other oxygenation
diffusion issues. In some neonatal patients HFOV may
be used as the first-line ventilator due to the high
susceptibility of the premature infant to lung injury from
conventional ventilation.
HFOV
Sensormedics 3100A
http://www.youtube.com/watch?v=UgaDa4jNYP0&feature=related
The 3100A has a diaphragmatically sealed piston driver. It is theoretically capable
of ventilating patients up to 30 kg. Tidal volume typically delivered ≈ 1.5-3.0 ml/kg
(< dead space). It is a efficient ventilator secondary to an active expiratory phase,
but it is not capable of delivering sigh breaths for alveolar recruitment.
SensorMedics 3100A Oscillatory
Ventilator
• INITIAL SETTINGS:
• FREQUENCY: Set initially at 10 Hz (600 BPM) for term infants and
15 Hz (900 BPM) for premature infants (< 2.5 kg). For children
between 6-10 kg, use 8 Hz, and for children > 10 kg, use 6 Hz for an
initial setting.
• INSPIRATORY TIME (I.T.): Set initially at 33% (e.g. 22 milliseconds
at 15 Hz, 41 milliseconds at 8 Hz, 55 milliseconds at 6 Hz).
• 1) Warning - The percent of I.T. should seldom be increased
because it will lead to air trapping and fulminate barotraumas.
Total I.T. should only be increased by decreasing frequency, thus
leaving the I:E ratio constant. I.T. can be decreased to 30% to heal
air-leaks.
• 2) I:E ratio: ≈ 1:2 for 3-15 Hz at 33% I.T.
•
•
The % Inspiratory time also controls the time for movement of the piston,
and therefore can assist with CO2 elimination.
Increasing % Inspiratory Time will also affect lung recruitment by increasing
delivered Paw.
SensorMedics 3100A Oscillatory
Ventilator
• POWER (AMP): A rough representation of the volume of gas
generated by each high frequency wave. Range (1.0 - 10.0).
• Maximum amplitude or volume delivered is highly variable and
depends on: circuit tubing (compliance, length and diameter),
humidifier (resistance and compliance - water level), ET tube
diameter and length
• 1) Set the POWER initially at 2.5 if wt <2.0 kg, 3.0 if wt < 2.5 kg, 4.0
if wt 2.5 - 4.0 kg, 5.0 if wt 4.0 - 5.0 kg, 6.0 if wt < 10 kg, 7.0 if wt > 20
kg.
• Check ABG's every 15-20 min until PaCO2≈ 40-60, i.e., titrate
POWER setting based on PaCO2 desired.
• Chest wall needs to be vibrating. If not vibrating, increase power.
• 2) Alveolar ventilation is directly proportional to POWER, so the
level of PaCO2 is inversely proportional to the power.
SensorMedics 3100A Oscillatory
Ventilator
• Amplitude is a measurement created by
the force that the piston moves which is
based on the POWER setting, resulting in
a volume displacement and a visual
CHEST WIGGLE. It is represented by a
peak to- trough pressure swing across
• the mean airway pressure.
SensorMedics 3100A Oscillatory
Ventilator
• MAP: Initial MAP 4 cm above MAP while on CMV
• Oxygenation on HFOV is directly proportional to MAP, which is
similar to CMV, however with the SensorMedics HFOV the MAP is
generated by PEEP. Thus during HFOV: MAP = PEEP.
• 1. Initial MAP Settings:
• a) Neonates - Initial MAP should be 2-4 cm above the MAP on CMV.
• b) Infants/Children - Initial MAP should be 4-8 cm above the MAP on
CMV.
• c) If starting immediately on HFOV - use a MAP of ≈ 8-10 cm in
neonates and 15-18 cm in infants/children.
• Check CXR 2 hrs after converting to HFOV, then adjust MAP to
achieve optimal lung volume (9-10 ribs expanded).
• If not oxygenating, increase MAP by 2 cm every hour until
oxygenation improves. Adjust Power to keep PaCO2 45-55.
Sensormedics 3100B
://www.youtube.com/watch?v=jLroOPoPlig
SensorMedics 3100B
Oscillatory Ventilator
• Initial Settings and Suggestions for Larger
Patient Use On 3100 B
• Patients with ARDS >35 Kg
• Set Paw 5 cmH20 above CV Paw
• FiO2 100%
• Set Hertz at 5-6
• Power 4.0, adjust for good chest wiggle
• I time % at 33%
• Set Bias Flow at >25 lpm, may need to go higher
SensorMedics 3100B
Oscillatory Ventilator
• Guidelines for Initial HFOV Settings:
• 1. Prior to initiating HFOV, perform a recruitment maneuver on the
oscillator by increasing Paw to 40 cmH2O for 30-40 seconds.
NOTE: the oscillator should be OFF during the maneuver.
Immediately abort the maneuver if hemodynamic compromise
occurs.
• 2. Set initial Paw at 5 cmH2O above conventional ventilator Pmaw.
• 3. Set power to achieve initial amplitude at chest oscillation to midthigh.
• 4. Set Hz at 5. Set IT to 33% (may increase to 50% if difficulty with
oxygenation; this may further raise carinal pressure an additional 2 –
4 cmH2O).
• 5. If oxygenation worsens, increase Pmaw in 2 – 3 cmH2O
increments q 30 minutes until maximum setting (approximately 45 –
55 cmH2O).
SensorMedics 3100B
Oscillatory Ventilator
• 6. If PaCO2 worsens (but pH > 7.2), increase amplitude in 10
cmH2O increments q 30 minutes up to the maximum setting. After
maximum amplitude is achieved, if necessary, decrease Hz to the
minimum setting of 3 Hz.
• 7. If severe hypercapnea occurs, with pH < 7.2, bag patient, set
maximum amplitude, Hz at 3, and try a small cuff leak (5 cmH2O
and then compensate bias flow); rule out endotracheal tube
obstruction.
• 8. If oxygenation improves, gradually wean FiO2 to 0.40, then slowly
reduce Pmaw 2-3 cmH2O q 4 – 6 hours until 22 – 24 cmH2O
range.
• 9. When the above goal is met, switch to PCV (initial settings: peak
pressure titrated to achieve delivered VT 6 ml/kg IBW, Pplat < 30 35 cmH2O), I:E 1:1, PEEP 12 cmH2O, rate 20 – 25,
• Paw should be 20 cmH2O (+/- 2 cmH2O).
SensorMedics 3100B
Oscillatory Ventilator
•
•
•
•
•
•
Hypercapnia
↑ delta P
Increase AMP
↓ frequency
↓ I time
(deflate cuff)
• Hypocapnia
↑ frequency
↓ delta P / AMP
SensorMedics 3100B
Oscillatory Ventilator
• Weaning – Wean FiO2 for arterial saturation > 90%
– Once FiO2 is 60% or less, re-check chest
x-ray and if appropriate inflation, begin
decreasing the Paw in 2 - 3 cmH2O
increments
– Wean Delta-P in 5 cmH2O increments for
PaCO2
• – Once the optimal frequency is found,
leave it alone
3100 A
3100 B
Limit Adjust
Button
No Limit
Adjust
Button
Piston
centering
adjustable
Piston
centering
connected
to
I/E Ratio
High Frequency Jet Ventilation
• This is the modification of a technique
initially developed to provide respiratory
support during bronchoscopy. Gas from a
high pressure source is delivered in short
bursts down a fine cannula, the tip of
which is lying within the endotracheal tube
and pointing down towards the periphery
of the lung
High Frequency Jet Ventilation
– Jet ventilator provides pulses of gas
– Conventional ventilator provides PEEP, FIO2
and sigh breaths for passive removal of
carbon dioxide
– Uses a flow interrupter that uses a pinch valve
to generate a stream of high frequency
pulses. These rapid pulses of fresh gas
generate the tidal volumes, which allow
ventilation to occur primarily from flow
streaming (Taylor Dispersion)
High Frequency Jet Ventilation
• A high pressure ‘’jet’’ of gas flows out of
the adaptor and into the airway. This jet of
gas occurs for a very brief duration, about
0.02 seconds, and at high frequency: 4-11
hertz. Tidal volumes ≤ 1 ml/Kg are used
during HFJV. This combination of small
tidal volumes delivered for very short
periods of time create the lowest possible
distal airway and alveolar pressures
produced by a mechanical ventilator.
Exhalation is passive
High Frequency Jet Ventilation
• Jet ventilators utilize various I:E ratios-between 1:1.1 and 1:12-- to help achieve
optimal exhalation. Conventional
mechanical breaths are sometimes used
to aid in reinflating the lung. Optimal PEEP
is used to maintain alveolar inflation and
promote ventilation-to-perfusion matching.
Jet ventilation has been shown to reduce
ventilator induced lung injury by as much
as 20%.
High Frequency Jet Ventilation
• A conventional ventilator is always run in tandem
with the jet to generate the PEEP and sigh
breaths. Expiration on HFJV is passive from
elastic recoil. A special ET adapter is used
during HFJV. This adapter has a jet port through
which the High Frequency Jet pulses are
introduced and a pressure monitoring port for
determining the delivered pressures.
• Expiration is passive, air-trapping can occur
High Frequency Jet Ventilation
• Aerosolized saline solution in the
inspiratory circuit is used to humidify the
inspired air. Some additional gas is
entrained during inspiration from a side
port in the circuit. This form of HFV
generally delivers a V of 2 to 5 mL/kg at a f
of 100 to 200 breaths/min. The jet
pressure (which determines the velocity of
air jets) and the duration of the inspiratory
jet (and, thus, the inspiratory/expiratory
ratio [I/E]) are controlled by the operator.
INITIAL HFJV SETTINGS
• A.) RATE (FREQUENCY) and INSPIRATORY TIME
• Initial Rate or Frequency - 420 BPM (7 Hz) is the usual
starting frequency for infants (range of 4 - 11 Hz or 240660 BPM). Start with 360 BPM (6 Hz) if either air leaks
or air trapping is a concern. Changes in rate or
frequency are rarely made in the hour-to-hour
management of blood gases.
• B.) I.T. - High Frequency Breath - always use 20
milliseconds (0.02 sec) for the inspiratory time (range
20-34 milliseconds). Any increase in I.T. will greatly
increase the risk of air trapping and pneumothorax.
INITIAL HFJV SETTINGS
•
•
•
•
C.) PIP (Peak Inspiratory Pressure)
The jet functions as a pressure limited ventilator.
Set the PIP that you want the jet to achieve.
The difference between the PIP ordered and the PEEP
is the delta P, which represents the volume of gas
generated by each high frequency pulse during the
opening of the pinch valve (maximum generated volume
occurs with a PIP of 50 cm with a minimum PEEP and
an IT of 34 milliseconds).
• Increase in PIP will increase delta P and improve
ventilation and a decrease in PIP will decrease delta P
and decrease ventilation.
• Initial PIP Settings: Range (8 - 50 cm H2O)
INITIAL HFJV SETTINGS
• D.) PEEP and Sigh Breaths
• The PEEP on HFJV is set by using the conventional
ventilator that is in-line with the jet. Oxygenation on
HFJV is directly proportional to MAP which is similar to
CMV; however, with HFJV, the MAP should be
generated primarily by PEEP with a contribution from the
PIP. The greater the delta P, the larger the
contribution of the PIP to the MAP.
• During HFJV; MAP should primarily be determined
by PEEP to avoid excessive use of PIP, thus
minimizing barotrauma, volutrauma, and hypocarbia.
Adjusting HFJV
• Appropriate adjustments when the arterial carbon dioxide tension
(PaCO2) is elevated include: increasing the driving pressure in 5 psi
increments to a maximum of 50 psi, increasing the inspiratory
fraction in 5 percent increments to a maximum of 40 percent,
increasing the frequency in 10 breaths per minute increments to a
maximum of 250 breaths per minute, or adding an another mode of
mechanical ventilation
• Appropriate adjustments when the arterial oxygen tension (PaO2) is
low include: adding applied PEEP in 3 to 5 cmH2O increments,
increasing the driving pressure by 5 psi increments to a maximum of
50 psi, or increasing the inspiratory fraction in 5 percent increments
to a maximum of 40 percent
HFJV
•
•
•
•
Advantages and Limitations
Used in tandem with CMV (IMV:0-5 bpm)
Not currently available outside the US
Can maintain oxygenation and ventilation over a
wide range of patient sizes and CL
• Works well in non-homogeneous lung diseases
• I-time and VT is held constant when rate is changed
so PaCO2 rises and falls intuitively as rate is lowered
and raised
• Very effective when low Paw is required: air leak
syndromes
High frequency percussive
ventilation (HFPV)
• Combines HFV plus time cycled, pressurelimited controlled mechanical ventilation
(ie, pressure control ventilation, PCV). It
can be conceptualized as HFOV
oscillating around two different pressure
levels, the inspiratory and expiratory
airway pressures
High frequency percussive
ventilation (HFPV)
• HFPV improves oxygenation,improves
ventilation, and lowers airway pressures
(peak, mean, and end-expiratory),
compared to other modes of mechanical
ventilation.
• HFPV is possible because of a device
called a phasitron. A phasitron is an
inspiratory and expiratory valve located at
the end of the endotracheal tube.
High frequency percussive
ventilation (HFPV)
• High-pressure gas drives the phasitron to
deliver small tidal volumes at a high
frequency (200 to 900 beats per min),
superimposed on the inspiratory and
expiratory airway pressures of PCV. PCV
is typically delivered at a respiratory rate of
10 to 15 breaths per min.
• HFPV does not require pharmacologic
• paralysis. In addition, it clears secretions
moreeffectively than other types of HFV
Differences in CMV, HFOV and HFJV pressure
waveforms
Assessment during HFV
• Frequent assessment of chest inflation both by clinical
signs (Chest wiggle) and chest radiographs (CXR) are
important during the clinical application of HFV
• You need to assess the amount of vibration being
produced. Vibration mainly in the neck could indicate a
dislodged ET tube and asymmetry vibration could
indicate pneumothorax. The vibration produced depends
on the amount of amplitude and lung compliance. Use a
visual assessment of the depth of bounce ranging from
the umbilicus to the clavicle.
• Assess Spo2, HR and TCO2 or ETCO2
• Obtain ABG’s through UAC line
Assessment during HFV
• Obtain the first x-ray at 1 hour preferably,
but no greater than 4 hour mark to
determine the lung volume at that time.
Paw may need to be read adjusted
accordingly.
• Always obtain a CXR , if unsure as to
whether the patient is hyper-inflated or has
de-recruited the lung.
Assessment during HFV
• Chest wiggle that is absent or becomes
diminished is a
• clinical sign that the airway or ET tube is
obstructed.
• CW present on one side only is an indication
that the ET tube has slipped down a primary
bronchus or a pneumothorax has occurred.
• Check the position of the ET tube or obtain a
CXR.
• Reassess CW following any position change.
Assessment during HFV
• 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.
• Blood Pressure. Be prepared for a potential
blood pressure drop; this is due to the increased
intra-thoracic pressure that oscillation can
cause, resulting in decreased venous return.
Assessment during HFV
• Auscultation:
Listening to breath sounds in infants ventilated
on HFOV may be helpful, as the sounds (friction
sounds) become reduced in the affected side
when the endotracheal tube is low and ventilates
only 1 lung or when a pneumothorax is present.
These changes may occur before the infant
becomes symptomatic. Thus auscultation should
be performed at the time of routine assessment
or if there is clinical deterioration
• Adventitious/Vesicular BS are not easily
auscultated
Assessment during HFV
• Suctioning
• Keep to a minimum and us In-line suction catheter
• Press Stop button briefly on SensorMedics while briefly
inserting and withdrawing catheter. PAW is maintained
throughout. You may increase Paw/FIO2 slightly
– Rationale for pausing – The oscillator causes a pressure pulse in
the airways. When suctioning if the sensormedics isn’t turned off
the secretions get pushed back down because of this pulse
pressure. So you are having ineffective clearance of secretions.
There is also the potential of air trapping with active piston
movement
– Push Reset button anytime ventilator becomes disconnected
and suddenly stops
Hazards to HFV
- Air-trapping causing lung over-inflation
- Improper sedation/fighting of ventilator
- Pulmonary interstitial emphysema
- Intraventricular haemorrhage &
periventricular leukomalacia
- Tracheal damage
- Sudden disconnect and alveolar collapse
- Noise pollution
Key points to starting HFV
• Choosing the RIGHT patient. HFV is NOT
for every patient
• When to Start?
Early application provides protection and
reduces incidence of further lung damage
• Rescue may or may not improve mortality
chances. The later HFV is started the less
chance of survival
Key Points
• Retrospective studies suggest that HFV
improves gas exchange in infants with severe
respiratory failure and hence reduces the need
for ECMO. The response rate to HFV appears to
be disease-specific. Infants who have
homogeneous lung diseases, such as RDS or
pneumonia, are more likely to respond more
favorably to HFV than those who have more
heterogeneous lung disease such as ARDS,
meconium aspiration pneumonia.
Key points to starting HFV
• Sedation/Paralytic may be required during
application of HFV
• Watch for sudden deterioration in vital signs
• Watch for Atelectasis and pneumothorax
• ALLOW FOR PERMISSIVE HYPERCAPNIA
Case Study:
• http://www.viasyshealthcare.com/prod_serv/dow
nloads/HFOVCaseStudy5_I.pdf
Nitric Oxide
• Nitric Oxide (NO) Therapy is used to relax
smooth muscle to improve blood flow to alveoli
to improve ventilation/perfusion mismatch,
decrease pulmonary vascular resistance,
decrease pulmonary pressures, improve
oxygenation and reduce need for ECMO
• NO acts as a specific pulmonary vasodilator
reducing PVR and pulmonary artery pressure
• Inhaled NO provides selective vasodilation of
the pulmonary arterioles without systemic effect.
Nitric Oxide
Nitric Oxide (NO), not to be confused with the anesthetic nitrous
oxideselective vasodilation properties.
NO is the active metabolite of a number of other vasodilators,
including sodium nitroprusside and nitroglycerin.
Produced in all human organ systems, including the nasopharynx
and lungs.
In high concentration, NO is profoundly toxic and causes disease
identical to Acute Respiratory Distress Syndrome (ARDS).
In presence of oxygen, NO is broken down to form nitrogen dioxide
(NO2). In the blood NO interacts with hemoglobin. The byproduct of
this reaction produces increased levels of methemoglobin.
Methemoglobin will not carry oxygen, and therefore, its level must
be closely monitored during NO therapy.
Nitric Oxide
• Nitric oxide is approved by the US Food and
Drug Administration for hypoxic respiratory
failure of the term and near-term newborn
• Hypoxic respiratory failure in neonates born at or
near term may be caused by such conditions as
primary persistent pulmonary hypertension,
respiratory distress syndrome, aspiration
syndromes, pneumonia or sepsis, and
congenital diaphragmatic hernia.
Nitric Oxide
• Inhaled nitric oxide
(iNO) is a selective
pulmonary vasodilator
for which the
mechanism of action
involves guanylyl
cyclase activation
leading to production
of cyclic guanosine
monophosphate and
subsequent smooth
muscle relaxation
Nitric Oxide
• Inhaled nitric oxide (INO) is indicated for:
• Hypoxic respiratory failure
• Newborns older than 34 weeks gestational age
who have either:
– Persistent pulmonary hypertension of the neonate
(PPHN)
– Congenital diaphragmatic hernia (CDH)
– Oxygenation index (OI) > 25
• A special ventilator injects NO into the ventilator
circuit. Key clinical information about INO
appears below.
Nitric Oxide
• NO diffuses into the vascular smooth
muscle cells adjacent to the endothelium
where it binds to and activates guanylyl
cyclase. This enzyme catalyzes the
dephosphorylation of GTP to cGMP, which
serves as a second messenger for many
important cellular functions, particularly for
signaling smooth muscle relaxation.
Nitric Oxide
• Cyclic GMP induces smooth muscle relaxation
by multiple mechanisms including
– Increased intracellular cGMP, which inhibits calcium
entry into the cell, and decreases intracellular calcium
concentrations
– Activates K+ channels, which leads to
hyperpolarization and relaxation
– Stimulates a cGMP-dependent protein kinase that
activates myosin light chain phosphatase, the enzyme
that dephosphorylates myosin light chains, which
leads to smooth muscle relaxation.
Nitric Oxide indications
• Inhaled nitric oxide (INO) is indicated for:
• Hypoxic respiratory failure
• Newborns older than 34 weeks gestational age
who have either:
– Persistent pulmonary hypertension of the neonate
(PPHN)
– Congenital diaphragmatic hernia (CDH)
– Oxygenation index (OI) > 25
• A special ventilator injects NO into the ventilator
circuit. Key clinical information about INO
appears below.
Application of NO
•
•
•
•
Dosing begins at 20 ppm
Wean by decreasing dose by ½ each time
Wean to 1 ppm
Increase FIO2 when discontinuing INO
– The PaO2 decreases when INO is discontinued
because the body needs time to increase NO
productionPotential problems
• NO + O2 → NO2; presence of nitrogen dioxide
(NO2) is not a problem at therapeutic doses
• NO + red blood cell → metHb; monitor levels
• INOvent delivery system is a
integrated, single unit,
designed to administer and
monitor inhaled NO. The
INOvent delivery system
connects to the inspiratory limb
of the patient breathing circuit.
It functions by measuring gas
flow in the breathing circuit
and injecting the required flow
of NO to deliver the
concentration set by the user
in parts per million.
Contraindications
Absolute contraindications:
• Patients with congenital or acquired
methemglobinemia reductase deficiency
Relative contraindications:
• Patients with a bleeding diathesis
Intracranial hemorrhage
• Severe left ventricular failure
Hazards
•
•
•
•
Elevated methemglobin levels
Nitrogen dioxide (NO2) toxicity
Prolongation of PT/PTT
Increased left ventricular filling associated
with rapid changes in pulmonary
pressures
• Rapid withdrawal of NO may result in
rebound hypoxemia and pulmonary
hypertension
Precautions
• When given via mechanical ventilator, an
increase in exhaled tidal volumes might be
noted. This increase occurs as a result of
additional gas flow from NO into the
circuitry.
• Trigger sensitivity of the ventilator might
be compromised, especially if the patient
is on an assisted mode of ventilation.
Monitoring while using NO
•
•
•
•
•
•
•
•
•
•
•
•
FiO2
Tidal volume
Trigger sensitivity
Pulse oximetry
Arterial blood gases must be obtained at baseline and as follows:
Post initiation
Each hour or PRN as needed for six hours
30 minutes after each NO concentration adjustment
At any time when clinically indicated
Pulmonary artery pressure
Platelet count
NO2 levels
http://inomax.com/
View InoMax MOA