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
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

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

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

8. Airway Loops
Flow - Volume Pressure - Volume

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

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

11. Flow Synchrony
 Flow synchrony is defined as the ideal
matching of inspiratory flow of a ventilator
breath to the patient'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

12. Flow Asynchrony

13. Flow Asynchrony

14. Flow Asynchrony

15. 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

16. 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

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

18. 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

19. Trigger Insensitivity

20. Trigger Insensitivity
15

21. 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”)

22. Air Leak

23. Air Leak

24. Autocycling

25. Autocycling

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

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

28. 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

29. Airway Obstruction – Secretions

30. Airway Obstruction – Secretions

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

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

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

34. 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

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

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

37. 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

38. 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 P) breaths

39. Intrinsic PEEP: Treatment
 No treatment
 expiratory time
– respiratory rate
– inspiratory time
–flow cycling of the breath

40. Intrinsic PEEP

42. 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

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

44. 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

45. Increased Expiratory Resistance

46. Increased Expiratory Resistance

47. Increased Expiratory Resistance

48. 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

49. 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