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 < 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 < 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 < 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.
I:E 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 patient’s 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 Froese, Anesth, 1974).
Maintaining spontaneous ventilation tends to improve ventilation-perfusion matching by preferentially providing ventilation to dependent lung regions that receive the best blood flow.

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 can’t 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 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 (Children’s 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 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.

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, Internat’l 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 cm H2O, according to the following chart.
T High/T low releases
T High (s) T low (s) Freq.
P/F MAP
<
<
<
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 I:E
Create releases and I:E

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 Elimination To 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 < 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 < 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

61. 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

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!