1. Interpretation of Ventilator Graphics
Dr.Ahmed Abd Elmaksoud, MD

2. What is ventilator waveform?

3. Parameters displayed in waveform:
Volume
Pressure
Flow
Time
Exhaled Pco2

4. Physics review
A pressure difference (∆p) must be present to make a fluid to flow
The higher the pressure difference the higher the flow
Flow is measured as the volume of the fluid passed a certain point in unit time,

5. Physics review The Resistance:
It is the pressure difference divided by the flow caused by it

6. Physics review The Compliance:
The compliance of a system is the volume change per unit change in pressure

7. Physics review The Work of Breathing:
It is the pressure difference across the system multiplied by the volume of the fluid moved by it

8. Ventilator Waveforms Depend on:
Mode of ventilation
Ventilator properties and settings
Respiratory properties of the patient

9. Types of Ventilator Waveforms
Scalar:
Pressure – time
Volume – time
Flow – time
Loops:
Pressure – volume
Volume – Flow
Flow – pressure
Trends:

10. Pressure – time curve Volume–oriented breath (modes)
Pressure–oriented breath (modes)

11. Pressure – time curve
Pressure – time curve shows airway pressure, breath timing, the breath type delivered and patient versus machine triggering

12. Pressure – time curve (volume – oriented mode)

13. Pressure – time curve (volume – oriented mode)

14. Pressure – time curve (volume – oriented mode)

15. Pressure – time curve (volume – oriented mode)
The level of pressure at “B” is affected by the resistance and the flow

16. Pressure – time curve (volume – oriented mode)
The level of the plateau pressure is determined by the compliance and the tidal volume

17. Pressure – time curve (volume – oriented mode)
Lung recruitment and leaks in the system are possible reasons for further slight decrease in pressure (points D to E).

18. Pressure – time curve (pressure – oriented mode)
In pressure-oriented ventilation, Pressure increases rapidly from the lower pressure level until it reaches the upper pressure value and then remains constant for the inspiration time set on the ventilator.

19. Pressure – time curve (pressure – oriented mode)

20. Flow – time curve
Constant flow is a typical feature of a classic volume – oriented mode of ventilation.

21. Flow – time curve

22. Flow – time curve
Decelerating flow is a typical feature of a pressure – oriented mode of ventilation.

23. Flow – time curve

24. Flow – time curve
The course of the flow curve during inspiration is strongly influenced by the ventilation mode set on the ventilator
The course of the flow curve during expiration is influenced by the overall resistance and compliance of the lung and the system.

25. Volume – time curve
The transferred volume is calculated as the area underneath the flow curve
The maximum volume value is the transferred tidal volume (not the entire volume in the lung)

26. Volume – time curve

27. Volume controlled ventilation
Pressure – volume loop
Volume controlled ventilation

28. Pressure controlled ventilation
Pressure – volume loop
Pressure controlled ventilation

29. Pressure support ventilation
Pressure – volume loop
Pressure support ventilation

30. Spontaneous ventilation
Pressure – volume loop
Spontaneous ventilation

31. Pressure – volume loop
The area to the left of the vertical axis (A) is a measure of how much work the patient needs to do to trigger the ventilator. The area to the right of the axis (B) represents the work done by the ventilator to support the patient

32. Pressure – volume loop
As compliance decreases, and the ventilator settings remain the same, the PV loop in volume-controlled ventilation takes an increasingly flat course.

33. Pressure – volume loop
The change in resistance during constant flow ventilation changes the position of the inspiratory branch of the loop while its steepness remains unchanged

34. Pressure – volume loop
A change in the height of the PV loop is a measure of the strength of the patient’s inspiratory effort (if the ventilator parameters are unchanged)

35. Pressure – volume loop

36. Pressure – volume loop

37. PV loops measured before and after resistances
Pressure – volume loop
PV loops measured before and after resistances

38. Pressure – volume loop
The work of breathing can be much greater than what is displayed in PV loops if the pressure is measured before resistances

39. Pressure – volume loop

40. Pressure – volume loop
The reason for setting assisted spontaneous breathing is generally to try to compensate for these airway resistance

41. Volume – flow loop
Changes in the shape of volume – flow loop are used to obtain information about airway resistance

42. Increased airway resistance due to increased secretions
Volume – flow loop
Increased airway resistance due to increased secretions

43. Trends
Graphic trend displays enable ventilation processes to be assessed at a later stage.
An event which occurs suddenly calls for as much details as possible to be shown in the diagram; while assessing the process of weaning, for example, needs several days or even weeks to be displayed in one diagram.

44. Trends

45. Trends

46. Trends

47. What is going on here?

48. What is going on here?

49. What is going on here?

50. Air leak

51. Approximately 200ml of volume is lost
Air leak
Approximately 200ml of volume is lost

52. Approximately 75ml of volume is lost
Air leak
Approximately 75ml of volume is lost

53. What is going on here?

54. What is going on here?

55. Auto - PEEP

56. Auto - PEEP

57. Auto - PEEP
The presence of positive pressure in the lung at the end of exhalation due to air trapping Causes: Insufficient expiratory time Increased expiratory resistance Early collapse of unstable airway

58. Resistance changes

59. Resistance changes

60. Resistance changes

61. Resistance changes

62. Compliance changes

63. Compliance changes

64. Over-distention

65. Flow asynchrony (flow starvation)

66. Flow asynchrony (flow starvation)

67. Cycling asynchrony

68. Cycling asynchrony

69. trigger asynchrony

70. Thank you