1. Airway Graphic Analysis to
Optimize Patient-Ventilator
Interactions
Ira M. Cheifetz, MD, FCCM, FAARC
Professor of Pediatrics
Chief, Pediatric Critical Care
Medical Director, Pediatric ICU
Duke Children’s Hospital

2. Case Scenario
♦ 5 mo (former 27 wk gestation) with CLD admitted
with RAD exacerbation & viral pneumonia.
♦ Intubated shortly after admission for impending
resp failure.
♦ PC/PS: RR 28, PIP 28, PEEP 7, PS 12
♦ Sedated with infusions of midazolam & fentanyl.
♦ Infant experiences an acute episode of
tachypnea, subcostal retractions, and agitation.

3. Case Scenario
Time-based capnogram & airway scalars
(pressure vs. time and flow vs. time) are:

4. Case Scenario
The patient’s acute change in clinical
status is most consistent with:
a.) worsening bronchospasm
b.) pain
c.) flow asynchrony
d.) trigger insensitivity
e.) air trapping

5. Goal: Airway Graphic Analysis
♦ Optimize mechanical ventilation by
diagnosing and correcting abnormalities
in the interaction between the patient and
the ventilator.

6. Airway Scalars
Paw (cm H2O)
Flow (L/min)
Vt (ml)

7. Airway Loops
Flow - Volume Pressure - Volume

8. Patient - Ventilator Interactions
♦ Facilitate spontaneous breathing
♦ Optimize patient WOB
♦ Maximize pt-ventilator synchrony
– inspiratory synchrony
– expiratory synchrony

9. Patient - Ventilator Interactions
♦ Inspiratory synchrony
–flow synchrony
–trigger synchrony
–ETT effects / airleak
–avoid overdistention
♦ Expiratory synchrony

10. Flow Synchrony
♦ Flow synchrony is defined as the ideal
matching of inspiratory flow of a ventilator
breath to the pt's inspiratory demand
during assisted or supported ventilation.
♦ Asynchrony: Inadequate inspiratory flow
at any point during inspiration causing an
increased or irregular pt effort.
– leads to increased WOB
– “fighting” the ventilator

11. Flow Asynchrony

12. Flow Asynchrony

13. Flow Asynchrony

14. Optimal Pt - Vent Synchrony
♦ Allows for optimal use of nutritional
support
– Slutsky, Chest, 1993
♦ Decreases VILI in neonates
– Rosen, Ped Pulm, 1993
♦ Improves pt comfort and reduces
work of breathing
– Ramar, Respir Care Clin, 2005

15. Patient - Ventilator Synchrony
♦ Pt-vent synchrony should be optimized by
assessing the pt - ventilator interface
before administering sedation.
♦ Increased sedative use in the 1st 24 hrs of
ventilation ↑ LOV in pediatric pts with ALI.
– Randolph (PALISI Network), JAMA, 2002

16. Patient - Ventilator Interactions
♦ Inspiratory synchrony
–flow synchrony
–trigger synchrony
–ETT effects / airleak
–avoid overdistention
♦ Expiratory synchrony

17. Trigger Sensitivity
♦ Trigger sensitivity = pt effort required to
initiate a ventilator assisted breath
♦ A determinate of pt effort required (WOB)
♦ What affects trigger sensitivity?
– pressure vs. flow triggering
– proximal vs. distal sensing
– ETT leaks / size

18. Trigger Insensitivity

19. Trigger Insensitivity
15

20. Effects of ETT Leaks on Triggering
♦ Problem
– ETT leak results in ↓ in airway
pressure and/or flow
– may be sensed as a patient effort
♦ Result
– may initiate a ventilator assisted
breath in the absence of a patient
effort (“autocycling”)

21. Air Leak

22. Air Leak

23. Autocycling

24. Autocycling

25. Patient - Ventilator Interactions
♦ Inspiratory synchrony
–flow synchrony
–trigger synchrony
–ETT effects / airleak
–avoid overdistention
♦ Expiratory synchrony

26. Pulmonary Injury Sequence
Froese, CCM, 1997
Froese, CCM, 1997
Two injury zones during mechanical ventilation

27. Overdistention
An ↑ in airway pressure at the end of inspiration
without a significant increase in delivered tidal
volume – ‘beaking’ at the end of inspiration.
C20 / Ctotal < 1.0

28. Airway Obstruction – Secretions

29. Airway Obstruction – Secretions

30. Inspiratory Synchrony
Optimal inspiratory patient - ventilator
synchrony is a function of:
♦inspiratory flow
♦trigger sensitivity
♦ETT effects
♦appropriate lung inflation

31. Patient - Ventilator Interactions
♦ Inspiratory synchrony
♦ Expiratory synchrony
–end-expiratory lung volume
–premature termination of
exhalation & intrinsic PEEP
–expiratory resistance

32. End-expiratory Lung Volume
♦ Lung volume prior to inspiration (FRC)
♦ A function of total PEEP and lung
compliance
Froese, CCM, 1997

33. End-expiratory Lung Volume
♦ If EELV is too low:
– lung compliance ↓, Vt ↓, RR ↑
– may result in premature termination of
exhalation & intrinsic PEEP
– ↑ opening pressure may result in
↑ risk of barotrauma
♦ If EELV is too high:
– pulmonary overdistention develops
– ↑ risk of volutrauma

34. Optimize PEEP
dynamic
vs. static
P-V curve

35. Patient - Ventilator Interactions
♦ Inspiratory synchrony
♦ Expiratory synchrony
–end-expiratory lung volume
–premature termination of
exhalation & intrinsic PEEP
–expiratory resistance

36. Premature Termination of Exhalation
♦ Failure of airway pressure, volume, &
exp flow to return to baseline prior to
the next vent assisted breath
♦ “Gas trapping” causes intrinsic PEEP

37. Intrinsic PEEP: Adverse Effects
♦ ↑ WOB
♦ ↑ mean intrathoracic pressure
♦ ↓ cardiac output
♦ ↓ trigger sensitivity
♦ ↓ Vt in pressure limited breath (set PIP)
♦ ↑ PIP in volume limited and pressure
control (set ΔP) breaths

38. Intrinsic PEEP: Treatment
♦ No treatment
♦↑ expiratory time
–↓ respiratory rate
–↓ inspiratory time
–flow cycling of the breath

39. Intrinsic PEEP

41. Intrinsic PEEP
♦ Reasons for intrinsic PEEP to occur:
–inadequate I:E ratio
–↑ respiratory rate
–inspiration is time cycled & not
responsive to changes in flow
♦ Goal:shorten inspiratory time while
maintaining appropriate tidal volume

42. Patient - Ventilator Interactions
♦ Inspiratory synchrony
♦ Expiratory synchrony
–end-expiratory lung volume
–premature termination of
exhalation & intrinsic PEEP
–expiratory resistance

43. Increased Expiratory Resistance
♦ Obstruction to exhalation caused by:
– airway obstruction – ETT occlusion
– bronchospasm
– blocked expiratory valve
♦ Prolonged expiratory phase causes:
– ‘gas trapping’
– ↑ WOB
– ↓ trigger sensitivity

44. Increased Expiratory Resistance

45. Increased Expiratory Resistance

46. Increased Expiratory Resistance

47. Expiratory Synchrony
Optimal expiratory patient - ventilator
synchrony is a function of:
♦ complete exhalation
♦ an ideal end-expiratory lung volume
♦ elimination of premature termination
of exhalation & intrinsic PEEP
♦ minimal expiratory resistance

48. Airway Graphics to Optimize
Patient - Ventilator Interactions
♦ Evaluate airway pressures & tidal volume
♦ Choose appropriate inspiratory flow
♦ Set trigger sensitivity appropriately
♦ Evaluate extent of air leaks
♦ Maintain adequate end-exp. lung volume
♦ Avoid intrinsic PEEP
♦ Minimize expiratory resistance

49. Case Scenario
♦ 5 mo (former 27 wk gestation) with CLD admitted
with RAD exacerbation & viral pneumonia.
♦ Intubated shortly after admission for impending
resp failure.
♦ PC/PS: RR 28, PIP 28, PEEP 7, PS 12
♦ Sedated with infusions of midazolam & fentanyl.
♦ Infant experiences an acute episode of
tachypnea, subcostal retractions, and agitation.

50. Case Scenario
Time-based capnogram & airway scalars
(pressure vs. time and flow vs. time) are:

51. Case Scenario
The patient’s acute change in clinical
status is most consistent with:
a.) worsening bronchospasm
b.) pain
c.) flow asynchrony
d.) trigger insensitivity
e.) air trapping