Transcript File - Respiratory Therapy Files

Airway Pressure Release
Ventilation (APRV)
Objectives
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Provide the definition and names for APRV
Explain the four set parameters.
Identify recruitment in APRV using exhaled
CO2.
Recommend appropriate initial settings for
APRV
Make adjustments based on arterial blood
gas results
Discontinue ventilation with APRV
Introduction
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Airway pressure release ventilation (APRV) is a
relatively new mode of ventilatory support that,
although outlined in 1987, did not become available
in the United States until the mid-1990s.
APRV augments alveolar ventilation. Airway
pressure is released from an elevated baseline
pressure to produce an expiration. The elevated
pressure facilitates oxygenation, while the pressure
release increases minute ventilation.
Introduction
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APRV has been successfully used in neonatal,
pediatric, and adult forms of respiratory failure.
Experimental and clinical use of APRV has been
shown to facilitate spontaneous breathing and is
associated with decreased peak airway pressures
and improved oxygenation/ventilation when
compared with conventional ventilation.
Additionally, improvements in hemodynamic
parameters, splanchnic perfusion, and reduced
sedation/neuromuscular blocker requirements have
been reported.
Introduction
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APRV may offer potential clinical advantages for
ventilator management of acute lung injury/acute
respiratory distress syndrome and may be
considered as an alternative “open lung approach”
to mechanical ventilation. Whether APRV reduces
mortality or increases ventilator-free days
compared with a conventional volume-cycled “lung
protective” strategy will require future randomized,
controlled trials
http://www.youtube.com/watch?v=BIT2Gy9nxp4
APRV Description
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A mode of ventilation along with
spontaneous ventilation to promote lung
recruitment of collapsed and poorly
ventilated alveoli.
The CPAP is released periodically for a brief
period.
The short release along with spontaneous
breathing promote CO2 elimination.
Release time is short to prevent the peak
expiratory flow from returning to a zero
baseline.
APRV
APRV (Airway Pressure
Release Ventilation)
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Provides two levels of CPAP and allows spontaneous breathing at
both levels when spontaneous effort is present
Both pressure levels are time triggered and time cycled
AKA
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BiVent – Servo
APRV – Drager
BiLevel – Puritan Bennett
APRV – Hamilton
Etc.
Lung Protective
Strategies
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Acute lung injury (ALI) and acute
respiratory distress syndrome (ARDS)
Keep plateau pressures < 30 cm H2O
Use low tidal volume ventilation (4-6
mL/kg IBW)
Use PEEP to restore the functional
residual capacity (FRC)
Lung Protective
Strategies
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As recently as 1993, the American College of Chest
Physicians (ACCP) consensus conference failed to
agree on an optimal mode of ventilation for any
disease state or an optimal method of weaning
patients from mechanical ventilation. The ACCP
agreed that well-controlled clinical trials that
defined the indications and uses of specific modes
of ventilation were lacking. Now, quite a few years
later, the hard science out there is still a bit scarce,
but, we have learned a few things.
Lung Protective
Strategies
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Recently, discovery of the potential for mechanical ventilation
to produce ventilator-associated lung injury has resulted in
the development of new lung protective strategies. Lung
protective strategies include those described in the open lung
approach promoted by Amato et al. The open lung
approach uses reduced tidal volumes (6 mL/kg or less)
to prevent high-volume lung injury and overdistension of alveoli.
In addition, Amato et al. used elevated end expiratory
pressure (average positive end-expiratory pressure
[PEEP] 16 cmH2O), to prevent low volume lung injury
from cyclic airway closure and re-opening.
Open the Lung and Keep
it Open
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ARDSNet study compared conventional tidal volume (mL/kg)
to reduced tidal volume (6 mL/kg).
The results of the ARDSNet trial and a study conducted by
Amato et al. suggest an association between reduced tidal
volume and improved outcome.
Improved outcomes seen in the ARDSNet study were a result
of not only reduced tidal volumes, but also increased PEEP
As a result, ARDSNet Assessment of Low tidal Volume and
Elevated end-expiratory volume to Obviate Lung Injury
(ALVEOLI) study was conducted to evaluate the role of higher
levels of PEEP on survival, results were inconclusive
Lung Recruitment
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Complete recruitment exceeds the lower inflection
point used by Amato et al. to determine optimal
PEEP levels. Recruitment begins at the lower
inflection point and continues to the upper
inflection point.
Therefore, elevated baseline airway pressure during
APRV may produce near complete recruitment, thus
minimizing low volume lung injury from cyclic
recruitment.
APRV is less likely to produce over-inflation or high-volume
lung injury, as airway pressures are lowered (released) in
order to accomplish ventilation.
Lung Recruitment
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Maintaining a constant airway pressure may be
advantageous for several reasons. Constant airway
pressure facilitates alveolar recruitment; enhances
diffusion of gases; allows alveolar units with slow
time constants to fill, preventing over-distension of
alveoli; and augments collateral ventilation. Van
Allen et al. noted that complete obstruction of an
airway unit did not always result in collapse of the
alveoli and, therefore, hypothesized that alternative
pathways must exist.
Lung Recruitment
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The pores of Kohn, located in the septa of
the alveoli and open only during inspiration,
first were believed to be responsible.
However, two additional pathways were
later credited with playing a role: (1)
Lambert's canals connect terminal and
respiratory bronchioles with adjacent
peribronchial alveoli, and (2) channels of
Martin interconnect respiratory bronchioles
and serve to bypass the main pathway
Keeping Plateau Pressure < 30 cm H20
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What do you do if CO2 is rising and
the plateau pressure is at 30 cm H2O?
– Change to pressure control/increase
rate/sedation
– Permissive hypercapnia?
– Low VT/high rates?
– HFVO?
– APRV…
Goals with APRV include
the following:
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Avoiding extension of lung injury
Minimal oxygen toxicity with high mean
airway pressure
Recruiting alveoli & preventing derecruitment
Minimizing peak airway pressure
Preventing atelectasis
Using sedation and paralysis
conservatively
Why APRV
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Clinicians have learned that cyclical opening and
closing of injured lung units damages them
(particularly if tidal volumes are large). We would
prefer if the patient could be ventilated at the top of
the volume pressure curve, at high lung volumes,
without phasic changes. This can be achieved using
high frequency oscillation, but adult oscillators are not
widely available. For the majority of patients,
increasing mean airway pressure without increasing
peak pressure means prolonging the inspiratory time
in a pressure control mode. The longer the inspiratory
time (Ti), the better the oxygenation benefit
Indications
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Primarily used as an alternative
ventilation technique in patients with
ARDS.
Used to help protect against ventilator
induced lung injury.
Indications
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The main causes of hypoxemia associated with ALI are
shunting due to alveolar collapse and reduction in functional
residual capacity. Therefore, a primary goal of the treatment
of ALI is recruitment of alveoli and prevention of derecruitment. Sustained plateau pressure is used to promote
alveolar recruitment, while being maintained at an acceptable
level [no more than 30 cmH2O, if possible].
In addition, the number of respiratory cycles is minimized to
prevent both the repetitive opening of alveoli and alveolar
stretch that may result in lung injury. Patients in early-phase
ALI often do not have impaired respiratory muscle strength or
inadequate respiratory drive. Frequently, CPAP alone is
sufficient to restore lung volume and increase lung
compliance. However, when assistance with ventilation is
required, APRV can be used. Intermittent airway pressure
release allows alveolar gas to be expelled via natural lung
recoil.
Goal
To provide the lung protective
ventilation supported by the ARDSnet
research.
Use an “Open lung” approach.
Minimize alveolar overdistension.
Avoid repeated alveolar collapse and
reexpansion.
Restore FRC through recruitment and,
Maintain FRC by creating intrinsic PEEP.
Consider APRV when the
Patient Has -
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Bilateral Infiltrates
PaO2/FIO2 ratio < 300 and falling
Plateau pressures greater than 30 cm
H2O
No evidence of left heart failure (e.g.
PAOP of 18 mm Hg or greater)
In other words, persistent ARDS
Possible Contraindications
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Unmanaged increases in intracraneal
pressure.
Large bronchopleural fistulas.
Possibly obstructive lung disease.
Technically, it may be possible to
ventilate nearly any disorder.
Terminology
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Four commonly used terms include: pressure high
(P High), pressure low (P Low), time high (T High),
and time low (T Low).
P High – the upper CPAP level. Analogous to MAP
(mean airway pressure) and thus affects
oxygenation. P High is the baseline airway pressure
level and is the higher of the two airway pressure
levels. Other authors have described P High as the
CPAP level, the inflating pressure, or the P1
pressure (P1), also called High Peep.
P-High
p-High is the upper CPAP or pressure
setting when utilizing APRV.
p-High regulates end-inspiratory lung
volume & is analogous with mean airway
pressure
Terminology
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PEEP (Also called Plow or Low Peep) is the lower
pressure setting.
P Low is the airway pressure level resulting from the
pressure release. Other authors may refer to P Low as
the PEEP level, the release pressure, or the P2 pressure
(P2).
P-Low
Servo I: Bi-Vent
Draeger Evita
The p-Low setting, sets the lower level of
CPAP during the release phase.
The term "p-Low" is used in Draeger &
Hamilton medical ventilators.
PB 840 BiLEVEL
T-High
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T High- is the inspiratory time IT(s)
phase for the high CPAP level (P
High).
T High corresponds with the length of
time for which P High is maintained
T-High
Allows for sustained recruitment allowing
for improved gas exchange by increasing
alveolar surface area.
T-Low
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T Low is the length of time for which
the P Low is held (i.e. for which the
airway pressure is released)
T High plus T PEEP (T low) is the total
time of one cycle.
I:E ratio becomes irrelevant because
APRV is really best thought of as CPAP
With occasional releases
T-Low
The t-Low sets the time interval for the low
pressure/CPAP phase (p-Low).
Allows for intermittent release in airway
pressure, providing paCO2 removal.
Partially unloads the patients work of breathing
associated with pure CPAP breathing.
The name "t-Low" is used in both Draeger and
Hamilton ventilators.
note- t-Low should not be considered
"expiratory time" as the patient may exhale
throughout the entire inspiratory phase.
When using Bi-Level on the PB 840 there is no
setting to set the low pressure interval. The
operator must change frequency & "TH" to set a
t-Low. This can become problematic when trying
to precisely set a t-Low interval.
APRV: Setting P-High based on the Static
Pressure Volume Curve
Some newer mechanical ventilators provide the
operator with automated tools to obtain a static
Pressure Volume (P/V) Curve in the ventilated patient.
These tools provide the clinician a simple, safe, and
reproducible method to assess the P/V curve for various
pulmonary conditions.
APRV: Setting P-High based on the Static
Pressure Volume Curve
For example many Respiratory care practitioners utilize the P/V to identify the
lower and upper inflection points. “The lower section of the P/V curve, where the
compliance is less favorable, corresponds to a condition in which a given number
of alveolar units are collapsed”
It is common for the practitioner to set Positive End-Expiratory Pressure (PEEP) 1to-2 cmH2O above the lower inflection point to prevent de-recruitment and
minimize injury related to shear stress from the repetitive opening and closing of
the alveoli.
The upper inflection point indicates a decrease in lung compliance and may specify
over-distention of the lung units.
The assessment of the static P/V curve can provide insight on how well a patient
will respond to the application of Airway Pressure Release Ventilation. Evaluation of
the “hysteresis” (difference between the inflation and the deflation limb) can
indicate the extent of potential lung units that may be recruited. If the patient has
very little probability for alveolar recruitment then APRV is less likely to be
beneficial and unjustified.
APRV: Setting P-High based on the Static
Pressure Volume Curve
If the patient meets indications for utilizing APRV, the operator can use
points on the P/V to safely set P-High.
P-High should be set always below the pressure which generated the “Upper
Inflection Point”.
P-High can be set 1-to-2 cmH2o above the “Lower Inflection Point”.
The practitioner can calculate “Best Compliance” and set P-High according
to the pressure that generated the best compliance (some P/V tools
automatically calculate this).
The static P/V curve provides a more diagnostic and patient tailored
approach to setting P-High.
P/V Tool for more intelligent patient assessment
The automated P/V Tool uses an empirical and repeatable method to find best
PEEP, based on respiratory mechanics.
It also enables sophisticated lung recruitment maneuvers and therapy
assessment.
This maneuver records the static pressure/volume curve quickly and easily at
the bedside. It employs an adjustable pressure ramp, in which airway pressure
is slowly increased to an upper limit as resultant volume and pressure are
recorded.
After the maneuver, the cursor function lets you inspect inflection points so that
you can easily visualize the linear portion of the compliance curve.
Advantages of APRV
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Uses lower PIP to maintain oxygenation
and ventilation without compromising the
patient’s hemodynamics (Syndow AJRCCM 1994, Kaplan,
CC, 2001)
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Shown to improved V/Q matching (Putensen,
AJRCCM, 159, 1999)
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Required a lower VE suggesting reduced
VD/VT (Varpula, Acta Anaesthesiol Scand 2001)
APRV vs. PCIRV
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Although both modes increase PAW,
PCIRV usually requires higher PIP and
heavy sedation/paralytic, whereas
APRV allows for spontaneous
breathing
Increases cardiac index
Decreases central venous pressure
Additional Advantages Compared to PCIRV
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APRV increases oxygen delivery and
Reduces the need for sedation and
paralysis
APRV also improves renal perfusion
and urine output when spontaneous
breathing is maintained. (Kaplan, Crit Care, 2001;
Hering, Crit Care Med 2002)
APRV vs. SIMV
Conventional vs APRV
Advantages of Spontaneous
Breathing
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The benefits of APRV may be related to the
preservation of spontaneous breathing.
Maintaining the normal cyclic decrease in
pleural pressure, augmenting venous return
and improving cardiac output. (Putensen, AJRCCM,
1999)
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The need for sedation is decreased.
Preserve Spontaneous Breathing
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The dashed line in each figure represents
the normal position of the diaphragm.
The shaded area represents the
movement of the diaphragm. (Froese, 1974)
Spontaneous v.s. Paralyzed
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Spontaneous breathing provides ventilation to
dependent lung regions which get the best blood
flow, as opposed to PPV with paralyzed patients.
((Frawley, AACN Clinical 2001. Froese, Anesth, 1974).
Spontaneous v.s.
Paralyzed
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During PPV (paralyzed patient), the
anterior diaphragm is displaced
towards the abdomen with the nondependent regions of the lung
receiving the most ventilation where
perfusion is the least.
Other Advantages of
Spontaneous Breathing
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Reduces atrophy of the muscles of
ventilation associated with the use of PPV
and paralytic agents. (Neuman, ICM,2002)
Another Advantage
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During PPV atelectasis formation can
occur near the diaphragm, when
activity of this muscle is absent.
(paralysis)
However, if spontaneous breathing is
preserved, the formation of atelectasis
is offset by the activity of the
diaphragm. (Hedenstierna, Anesth, 1994)
Initial Settings – P High
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P High – Set a plateau pressure (adult)
or mean airway pressure (pediatric)
Typically about 20-35 cm H2O.
In patients with Pplateau at or above
30 cm H2O, set at 30 cm H2O
http://www.youtube.com/watch?v=y
W-S2ZGLRqs&feature=related
Setting Phigh
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Over-distention of the lung must be
avoided. Maximum Phigh of 35 cm H2O.
(controversial)
Exceptions for higher settings – morbid
obesity, decreased thoracic or
abdominal compliance (ascites).
Setting Thigh
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The inspiratory time (Thigh) is set at a
minimum of about 4.0 seconds
In children, others use lower settings
(Children’s Med Ctr. Uses 2 sec.)
Thigh is progressively increased (10 to
15 seconds (Habashi, et al)
Target is oxygenation.
Setting Thigh
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Progress slowly. For example, 5 sec
Thigh to 0.5 sec Tlow, a 10:1 ratio.
Increasing to 5.5 sec to 0.5 sec is an
11:1 ratio; not a big change.
Old patients may be fragile.
APRV
Release Time - TPEEP
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Currently, with ARDS thinking is not to
let exhalation go to complete
emptying, i.e. do not let expiratory
flow returning to zero. (McCunn, Crit Care
2002)
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Thus, regional auto-PEEP a desirable
outcome with APRV
FLOW
Setting PEEP or Plow in
APRV
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Set PEEP at zero cm H2O.
This provides a rapid drop in pressure, and
a maximum DP for unimpeded expiratory
gas flow. (Frawley, AACN Clin Issues 2001)
Avoid lung collapse during Tlow.
Establishing T PEEP
(Time at low pressure)
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Set T PEEP (T low) so that expiratory
flow from patient ends at about 50 to
75% of peak expiratory flow.
This can be determine saving a screen
and calculating peak expiratory flow.
Or, it can be estimated
Expiratory Flow
T PEEP – Setting The Time
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Adults 0.5 to 0.8 seconds
Pediatric/neonatal settings 0.2 to 0.6
seconds.
Or one time constant. (TC = C x R)
T PEEP – Using the Tc
Release Time in ARDS
Atelectasis can develop in
seconds when Paw
drops below a critical
value in the injured
lung. (Neumann P, JAP 1998, Newmann P,
AJRCCM 1998, Frawley, 2001; McCunn, Internat’l
Anesth Clinics 2002).
Too long a release time
would interfere with
oxygenation and allow
lung units to collapse.
Initial Settings
P high 20-30 cm H2O, according
to the following chart.
P/F
<250
<200
<150
MAP
15-20
20-25
25-28
T high range 4-6 sec.
T low = 0.5 sec and
P low = 0
T High/T low- 12-16 releases
T High (s) T low (s) Freq.
3.0
0.5
17
4.0
0.5
13
5.0
0.5
11
6.0
0.5
9
PS- as indicated with
special attention given to
PIP.
Review of Settings
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http://www.youtube.com/watch?v=y
W-S2ZGLRqs&feature=related
Waveform Review
Airway Pressure Release Ventilation (APRV) showing the characteristic long
inspiratory time (TIMEH) (A) and short "release" time (TIMEL) (B). Note
that all spontaneous breathing occurs at PEEPH. [Note: Our module on
APRV applies generally to all variations popularly used].
Bi-Vent Settings
Set Releases and I:E
Create releases and I:E
Bi-Vent Ventilation
P High
T PEEP
T High
Spontaneous Breathing
Spontaneous Breaths (On P High)
Patient Trigger
(On P High)
Spontaneous Breathing w/PS
Spontaneous Breaths w/PS
Identifying Lung Recruitment
– CO2 Monitoring
Making Changes in APRV
Settings Based on ABGs
Control Settings for CO2
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DP (Phigh – Plow) determines flow out of
the lungs and volume exchange (VT and
PaCO2).
Some clinicians suggest a target minute
ventilation of 2 to 3 L/min. (Frawley,
2001).
Optimize spontaneous ventilation.
CO2 Elimination
To Decrease PaCO2:
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Decrease T High.
–
–
–
–
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Shorter T High means more release/min.
No shorter than 3 seconds
Example: T High 5 sec. = 12 releases/min
T High 4 sec = 15 releases/min
Increase P High to increase DP and volume
exchange. (2-3 cm H2O/change)
– Monitor Vt
– PIP (best below 30 cm H2O)
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Check T low. If possible increase T low to allow
more time for “exhalation.”
To Increase PaCO2
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Increase T high. (fewer releases/min)
Slowly! In increments of 0.5 to 2.0
sec.
Decrease P High to lower DP.
– Monitor oxygenation and
– Avoid derecruitment.
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It may be better to accept hypercapnia
than to reduce P high so much that
oxygenation decreases.
Management of PaO2
To Increase PaO2
1. Increase FIO2
2. Increase MAP by increasing P High in 2
cm H2O increments.
3. Increase T high slowly (0.5 sec/change)
4. Recruitment Maneuvers
5. Maybe shorten T PEEP (T low) to increase
PEEPi in 0.1 sec. increments (This may
reduce VT and affect PaCO2)
Weaning From APRV
1.
2.
3.
FiO2 SHOULD BE WEANED FIRST. (Target <
50% with SpO2 appropriate.)
Reducing P High, by 2 cmH20 increments until
the P High is below 20 cmH2O.
Increasing T High to change vent set rate by 5
releases/minute
Weaning From APRV
3.
4.
The patient essentially transitions to
CPAP with very few releases.
Patients should be increasing their
spontaneous rate to compensate.
During Weaning
Add Pressure Support judiciously.
Add Pressure Support to P High in order
to decrease WOB while avoiding overdistention,
P High + PS < 30 cmH2O.
Pressure Support with
APRV
Pressure Support with
APRV
60
PEEPHigh + PS
PEEPH
Paw
PEEPL
cmH20
-20
Pressure Support
1
2
3
4
5
6
7
Weaning Bi-Vent
Lower Rate
Longer T High
Lower P High
Add PS
Weaning Bi-Vent
Lower Rate
Longer T High
Add PS
Lower P High
Weaning- Habashi method: Drop-and-Stretch
Perceived Disadvantages
of APRV
APRV is a pressure-targeted mode of
ventilation.
Volume delivery depends on lung
compliance, airway resistance and the
patient’s spontaneous effort.
APRV does not completely support CO2
elimination, but relies on spontaneous
breathing
Disadvantages of APRV

With increased Raw (e.g.COPD)
– the ability to eliminate CO2 may be more difficult
– Due to limited emptying of the lung and short
release periods.

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If spontaneous efforts are not matched
during the transition from Phigh to Plow and Plow
to Phigh, may lead to increased work load and
discomfort for the patient.
Limited staff experience with this mode may
make implementation of its use difficult.
The End

Lesson 1 Lab: Setup and manipulation of
APRV on the Galileo ventilator and BiLevel
on the PB 840. Use of clinical scenarios will
be used to guide decision making.

Lesson 1 assignment: Analyze current
evidence based research on the use of APRV
as a measure to decrease mortality in the
ARDS patient. Write a minimum of 3 pages
utilizing peer reviewed articles and APA
referencing to support or refute APRV use
as primary means to decrease mortality.