The

1
The How To of BiVent (APRV)

• David Pitts II, RRT
• Clinical Applications Specialist, Maquet
• Birmingham, Alabama
• Sponsored by Maquet, Inc Servo Ventilators

2
Objectives

• 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

3
Lung Protective Strategies

• Acute lung injury (ALI) and acute respiratory
  distress syndrome (ARDS)
• Keep plateau pressures lt 30 cm H2O
• Use low tidal volume ventilation (4-6 mL/kg IBW)
• Use PEEP to restore the functional residual
  capacity (FRC)

4
Keeping Plateau Pressure lt 30 cm H20

• What do you do if CO2 is rising and the plateau
  pressure is at 30 cm H2O?

5
Alternative Techniques

• Increase the ventilator rate
• Permissive Hypercapnia
• Airway Pressure Release Ventilation
• High Frequency Ventilation
• Extracorporeal Life Support

6
Indications

• Primarily used as an alternative ventilation
  technique in patients with ARDS.
• Used to help protect against ventilator induced
  lung injury.

7
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.

8
APRV Description

• 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.

9
Ventilation With APRV

• 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.

10
APRV
11
AKA

• BiVent Servo
• APRV Drager
• BiLevel Puritan Bennett
• APRV Hamilton
• Etc.

12
Consider APRV when the Patient Has --

• Bilateral Infiltrates
• PaO2/FIO2 ratio lt 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

13
Possible Contraindications

• Unmanaged increases in intracraneal pressure.
• Large bronchopleural fistulas.
• Possibly obstructive lung disease.
• Technically, it may be possible to ventilate
  nearly any disorder.

14
Terminology

• P High the upper CPAP level. Analogous to MAP
  (mean airway pressure) and thus affects
  oxygenation
• PEEP (Also called Plow) is the lower pressure
  setting.
• T High- is the inspiratory time IT(s) phase for
  the high CPAP level (P High).
• T PEEP or T low- is the release time allowing CO2
  elimination

15
Terminology

• T High plus T PEEP (T low) is the total time of
  one cycle.
• IE ratio becomes irrelevant because APRV is
  really best thought of as CPAP
• With occasional releases

16
Bi-Vent Set-up Screen
17
Advantages of APRV

• Uses lower PIP to maintain oxygenation and
  ventilation without compromising the patients
  hemodynamics (Syndow AJRCCM 1994, Kaplan, CC,
  2001)
• Shown to improved V/Q matching (Putensen, AJRCCM,
  159, 1999)
• Required a lower VE suggesting reduced VD/VT
  (Varpula, Acta Anaesthesiol Scand 2001)

18
Compared to PCIRV Advantages of APRV

• APRV uses lower peak and mean airway pressures,
• Increases cardiac index,
• Decreases central venous pressure,

19
Additional Advantages - Compared to PCIRV

• 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)

20
New Water Coolers are Being Installed in the ICU
Waiting Rooms
21
Advantages of Spontaneous Breathing

• 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)
• The need for sedation is decreased.

22
Preserve Spontaneous Breathing

• The dashed line in each figure represents the
  normal position of the diaphragm.
• The shaded area represents the movement of the
  diaphragm. (Froese, 1974)

23
Spontaneous v.s. Paralyzed

• 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).

24
Spontaneous v.s. Paralyzed

• During PPV (paralyzed patient), the anterior
  diaphragm is displaced towards the abdomen with
  the non-dependent regions of the lung receiving
  the most ventilation where perfusion is the least.

25
Try as we might. We cant get away from it?
26
Other Advantages of Spontaneous Breathing

• Reduces atrophy of the muscles of ventilation
  associated with the use of PPV and paralytic
  agents. (Neuman, ICM,2002)

27
Another Advantage

• 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)

28
Initial Settings P High

• 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

29
Setting Phigh

• 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).

30
Setting Thigh

• The inspiratory time (Thigh) is set at a minimum
  of about 4.0 seconds
• In children, others use lower settings
  (Childrens Med Ctr. Uses 2 sec.)
• Thigh is progressively increased (10 to 15
  seconds (Habashi, et al)
• Target is oxygenation.

31
Setting Thigh

• Progress slowly. For example, 5 sec Thigh to 0.5
  sec Tlow, a 101 ratio.
• Increasing to 5.5 sec to 0.5 sec is an 111
  ratio not a big change.
• Old patients may be fragile.

32
APRV
33
Release Time - TPEEP

• 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)
• Thus, regional auto-PEEP a desirable outcome with
  APRV

FLOW
34
Setting PEEP or Plow in APRV

• 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.

35
Establishing T PEEP (Time at low pressure)

• 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

36
Expiratory Flow
37
T PEEP Setting The Time

• Adults 0.5 to 0.8 seconds
• Pediatric/neonatal settings 0.2 to 0.6 seconds.
• Or one time constant. (TC C x R)

38
T PEEP Using the Tc
39
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, Internatl Anesth Clinics
  2002).
• Too long a release time would interfere with
  oxygenation and allow lung units to collapse.

40
Rat Lung Model Dr. Slutsky
41
Initial Settings

• P high 20-30 cm H2O, according to the following
  chart.

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
P/F MAP lt250 15-20 lt200
20-25 lt150 25-28
T high range 4-6 sec.

• PS- as indicated with special attention given to
  PIP.

• T low 0.5 sec and
• P low 0

42
Bi-Vent Settings
Set Releases and IE
Create releases and IE
43
Bi-Vent Ventilation
P High
T PEEP
T High
44
Spontaneous Breathing
Spontaneous Breaths
(On P High)
Patient Trigger
(On P High)
45
Spontaneous Breathing w/PS
Spontaneous Breaths w/PS
46
Identifying Lung Recruitment CO2 Monitoring
47
Making Changes in APRV Settings Based on ABGs
48
Control Settings for CO2

• 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.

49
CO2 EliminationTo Decrease PaCO2

• Decrease T High.
• 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)
• Check T low. If possible increase T low to allow
  more time for exhalation.

50
To Increase PaCO2

• 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.
• It may be better to accept hypercapnia than to
  reduce P high so much that oxygenation decreases.

51
Management of PaO2

• To Increase PaO2
• Increase FIO2
• Increase MAP by increasing P High in 2 cm H2O
  increments.
• Increase T high slowly (0.5 sec/change)
• Recruitment Maneuvers
• Maybe shorten T PEEP (T low) to increase PEEPi in
  0.1 sec. increments (This may reduce VT and
  affect PaCO2)

52
Going Too Fast
53
Weaning From APRV

• FiO2 SHOULD BE WEANED FIRST. (Target lt 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

54
Weaning From APRV

• The patient essentially transitions to CPAP with
  very few releases.
• Patients should be increasing their spontaneous
  rate to compensate.

55
During Weaning

• Add Pressure Support judiciously.
• Add Pressure Support to P High in order to
  decrease WOB while avoiding over-distention,
• P High PS lt 30 cmH2O.

56
Pressure Support with APRV
57
Weaning Bi-Vent
Lower Rate
Longer T High
Add PS
Lower P High
58
Weaning Bi-Vent
Lower Rate
Longer T High
Add PS
Lower P High
59
(No Transcript)
60
(No Transcript)
61
Perceived Disadvantages of APRV

• APRV is a pressure-targeted mode of ventilation.
• Volume delivery depends on lung compliance,
  airway resistance and the patients spontaneous
  effort.
• APRV does not completely support CO2 elimination,
  but relies on spontaneous breathing

62
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.
• 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.

63
The End Thank You!