1. Neonatal Ventilation: “The Bivent”
Paul Kingma, MD PhD

2. Ventilation Basics: Goals
Oxygenation
FiO2
Mean airway pressure
Ventilation
Respiratory rate
Tidal volume

3. Conventional Pressure Ventilation
Itime
PIP
Pressure PS
PEEP
Time

4. Conventional Pressure Ventilation
How do you improve oxygenation?
Itime
PIP
Pressure PS
PEEP
Time

5. Conventional Pressure Ventilation
How do you improve oxygenation?
Itime
PIP
Pressure PS
PEEP
Time

6. Conventional Pressure Ventilation
How do you improve ventilation?
Itime
PIP
Pressure PS
PEEP
Time

7. What do you do?
If a 2700g intubated baby has oxygen sats 70% and pCO2 80 and…
30%FiO2 and ventilator settings of 16/5 and rate of 20?
100%FiO2 and ventilator settings of 28/7 and rate of 60?

8. Risk of Lung Injury

9. Conventional Pressure Ventilation
How do you improve oxygenation?
Itime
PIP
Pressure PS
PEEP
Time

10. Conventional Pressure Ventilation
How do you improve oxygenation? LONG I time
Itime
PIP
Pressure PS
PEEP
Etime
Time

11. Reynolds and Strang: 1970’s
Inverse I:E ratio
Improve oxygenation in neonates

12. Inverse I:E in infants = Air Leak
Factors associated with pulmonary air leak in premature infants receiving mechanical ventilation. Jpeds 1983 R.A. Primhak
Compare infants with pneumothorax vs ventilated controls
“No significant difference was found between the groups in any clinical factor, nor in any maximum ventilator setting other than a longer maximum inspiratory time in the study group.”

13. Conventional Pressure Ventilation
How do you improve oxygenation? LONG I time
Problem: Inverse I:E…Breath Stacking…Pneumothorax
PIP
Pressure PS
PEEP
Time

14. Is there a better way to increase Itime?

15. Another Option: Airway Pressure Release Ventilation (APRV)
Think of it as sustained high CPAP with timed “releases” to encourage ventilation
High and low CPAP settings: P high and P low
Baseline is at P high with pressure released periodically to allow ventilation
Release time is short to prevent collapse
Spontaneous exhalation allowed during ALL phases of respiratory cycle.
Therefore no breath stacking and no pneumothorax

17. Potential Advantages: Adults
Uses lower PIP to maintain oxygenation and ventilation without compromising the patient’s hemodynamics (Syndow AJRCCM 1994, Kaplan, CC, 2001)
Longer I-time means higher mean airway pressure with lower peak pressures
Shown to improved V/Q matching (Putensen, AJRCCM, 159, 1999)
Decreases dead space ventilation
Longer I-time allows diffusion of gases
Spontaneous respiration may
reduce need for sedation and avoid large changes in CO2 (Ratheberger, 1997; Putensen 2001)
improved ventilation in dependent lung regions
Better cardiac filling when compared to HFOV
Reduces time at extremes of pressure volume curve
decreased atelectasis
decreased barotrauma

18. What about Pediatrics?
Very little data

19. What about Pediatrics? Schultz, et al Crit Care Med 2001
Cross over study from SIMV to APRV or reverse in 15 patients with mild to moderate lung disease
Findings
Comparable oxygenation and ventilation with significantly lower peak pressures (33 vs 19 cm H2O)
No change in hemodynamic variables

20. What about Pediatrics? Krishnan, et al Ped Pulmonol, 2007
Case series of 7 pts (age 1 – 16 years)
Findings
Oxygenation (decrease in OI) improved with APRV over time
No problems with ventilation
No change in sedation requirements but No patients required neuromuscular blockade
No change in hemodynamic stability
Easier pt care than with HFOV

21. What about Pediatrics? Dermirkol, et al Indian J Pediatr 2010
Case series of 3 patients ( mo old) changed from PC to APRV
Findings
FiO2 decreased from 0.97 to 0.68
Mean Airway pressure increased from 17.9 to 27 cm H2O
Tidal volume increased from 8.3 ml/kg to 13.2 ml/kg

22. What about Pediatrics? Kamath et al. Ped Pulmonol 2010
Retrospective study of 11 pts on APRV for 12 hours due to failed conventional vent.
Findings after 10 hrs on APRV
FiO2 decreased from 0.83 to 0.67
Mean airway pressure increased from 16.1 to 21.1 cm H2O
No change in HR, CVP, BP, UOP, IVF

23. What about Neonates? No Data
Neonatal Sheep. Martin et al, 1991 Crit Care Med
Compared with PPV, APRV provided similar ventilation and oxygenation with lower peak pressures and without compromising cardiovascular performance.

24. When we know NOTHING it is easy to be an expert!
APRV in Neonates
When we know NOTHING it is easy to be an expert!
This is where I come in 

25. APRV Terminology
AKA: Bivent (Servo), APRV (Drager and Hamilton), Bilevel (Puritan-Bennett)
P High - the upper CPAP level.
P Low - the lower CPAP setting.
T High - is the inspiratory time phase for the P High.
T Low - is the release time allowing gas exchange and CO2 elimination

27. Bi-Vent Ventilation
P High
T low
T High

29. How do you pick the settings?

30. Two Approaches Similar to Pressure Targeted Ventilation
Select Phigh and Plow based on expected upper and lower inflection points of pressure volume curve
1-3:1 inverse Thigh to Tlow ratio
Tlow long enough to allow minimal trapping of exhaled gas

31. Two Approaches “Habashi method”
Phigh set to plateau pressure in conv vent
Plow set to zero!
Thigh adjusted to determine desired “release rate”
Tlow adjusted to stop exhalation at 50-70% of peak-expiratory flow

32. What do we do in NICU? Initial Settings
Newly intubated
P high—set at desired plateau pressure (typically 13–24 cm H2O in NICU) to achieve oxygenation and chest rise
Absolute value (NOT relative to P Low)
Bivent requires lower peak pressures than SIMV because of longer I-time
P low—0-5 cm H2O (mostly 3 cm H2O)
“Set” value but often actual PEEP is higher because of limited exhalation time
T high—1–3 secs (1/0.2 = release rate of 50, 3/0.2 = release rate of 19)
Used to control release rate
Time in Bivent is an absolute value not a relative value
T low—0.2–0.4
Used to control alveolar recruiting, “actual” PEEP, and tidal volumes
More on this in a bit

33. In the NICU: Initial Settings
Transition from conventional ventilation
Phigh—peak airway pressure in pressure-cycled mode minus 2-4
PEEP—0-5 cm H2O
T high—1–3 secs (usually target similar rate)
T PEEP—0.2–0.4 sec
Transition from HFOV
Phigh—target mPaw equal to HFOV plus 0–2 cm H2O
T high—1–3 secs (use judgment to determine rate)
T PEEP—0.2–0.4

34. Adjusting Settings: Increase Oxygenation
Increase FiO2
MAP
Increase P high (1-2 cm per change)
Increase T high (will impact rate also)
Increase Pressure support
Unlike SIMV or AC
Plow in Bivent has minimal impact on oxygenation
Tlow does not impact oxygenation directly (may impact recruitment)

35. Adjusting Settings: Oxygenation
T high
Increasing T high will improve oxygenation by increasing time at P High and subsequently increasing mean airway pressure
Increasing T high will also worsen ventilation by decreasing the number of releases per minute
Therefore, when adjusting T high, make small changes ~10% to avoid dramatic shifts in both oxygenation and ventilation

36. Adjusting Settings: Increasing Ventilation
Increase P high to raise the tidal volume
Decrease T high to raise the number of releases per minute (may need to increase Phigh to produce same mean airway pressure
Increase PS
Decrease Plow – more later
Increase Tlow – more later

37. Plow Recommend set Plow at 0 cm H2O.
This provides a rapid drop in pressure, and a maximum pressure gradient for unimpeded expiratory gas flow during pressure release.
However, may lead to lung collapse if left unchecked….

38. Plow Reality Check
Adult literature (Habashi) recommends setting Plow at 0 cm H2O, but to avoid potential risk of severe collapse if Tlow is too long, I usually set Plow no lower than 2-3 cm in neonates.
This provides a rapid drop in pressure and a maximum pressure gradient for unimpeded expiratory gas flow during pressure release.
BUT if you are brave and need absolute maximum exhalation rate, then set Plow to 0 cm H20 but monitor very closely for changes in lung compliance and quickly make appropriate changes in Tlow
HOW do you adjust Tlow?

39. RT Comfort Zone
Tlow

40. Expiratory Flow Goal: Maximum ventilation without risk of atelectasis
De-recruitment
Recruitment
From Habashi, et al 2005

41. Tlow To avoid collapse Tlow
Set Tlow so that expiratory flow from patient ends at about 50 to 75% of peak expiratory flow
In practice, this is difficult with neonates
Can also look at “actual” PEEP on vent to determine how low of pressure patients lungs are actually seeing
Target “normal” actual PEEPS of 5 cm H2O
Tlow
Too little results in not enough tidal volume
Too much results in atelectasis
Will change as compliance changes

42. Bivent Weaning
With SIMV we wean by lowering PIP and increase time during expiratory phase of cycle.
If you do this in BIVENT, patient will develop collapse from too long of Tlow.
Therefore DO NOT WEAN RATE IN BIVENT BY INCREASING Tlow
With BIVENT you lower pressure and increase time during inspiratory phase of cycle.
Gradually lower Phigh to decrease mean airway pressure
Gradually increase T High to lower number of releases per minute (this will increase your mean airway pressure so you may need to decrease Phigh even more)
Eventually patient will wean to equivalent of CPAP PS
As settings decrease remember may need to adjust PS to help with increased respiratory work load

43. Bivent Weaning: Drop and Stretch

44. Things to keep in mind
Bivent is a pressure mode of ventilation and will not change in response to changes in lung compliance
Tlow must be monitored frequently for changes in expiratory flow
Airway plugging can significantly impact expiratory flow
Technically, without spontaneous breaths, Bivent is the same as AC with a long I time BUT…
Since patient initiated inhalation/exhalation can occur at P High, “breath stacking” should not occur and the risk of pneumothorax should be minimal
Limited data in pediatrics and no data in neonates

45. What is our experience so far?

46. The End
Questions?