The “How To” of BiVent
(APRV)
David Pitts II, RRT
Clinical Applications Specialist, Maquet
Birmingham, Alabama
Sponsored by Maquet, Inc – Servo Ventilators
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
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)
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?
Alternative Techniques
Increase the ventilator rate
Permissive Hypercapnia
Airway Pressure Release Ventilation
High Frequency Ventilation
Extracorporeal Life Support
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.
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.
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.
Ventilation With APRV
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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
AKA
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BiVent – Servo
APRV – Drager
BiLevel – Puritan Bennett
APRV – Hamilton
Etc.
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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P High – the upper CPAP level. Analogous to
MAP (mean airway pressure) and thus affects
oxygenation
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PEEP (Also called Plow) is the lower pressure
setting.
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T High- is the inspiratory time IT(s) phase for
the high CPAP level (P High).
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T PEEP or T low- is the release time
allowing CO2 elimination
Terminology
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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
Bi-Vent Set-up Screen
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)
Compared to PCIRV –
Advantages of APRV
APRV uses lower peak and mean
airway pressures,
 Increases cardiac index,
 Decreases central venous pressure,
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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)
New Water Coolers are
Being Installed in the ICU
Waiting Rooms
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.
Try as we might. We can’t
get away from it?
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 20-25 cm H2O.
In patients with Pplateau at or above
30 cm H2O, set at 30 cm H2O
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.
Rat Lung Model –
Dr. Slutsky
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.
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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–
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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)
Going Too Fast
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
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
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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
Thank You!