Ventilación Mecánica

1. WHAT DO GRAPHICS TELL
YOU ?
DR.RAJESH.V
MD (chest), DNB (Resp Med)
IDCC (Critical Care)
Associate Professor, AIMS

2. PREPARING…

3. WHAT AM I UP TO ?
• Familiarize clinicians with
– Common patterns of ventilator graphics
encountered in the ICU
• Recognize the normal scalar and loop
graphics
– Its different components
• Recognize abnormalities in each
• Identify mode of ventilation from the
graphics
• What did I learn ?

4. NUMBERS Vs GRAPHICS
• NUMBERS
• Apparently objective
• May be easier for
beginners
• Provide less information
• Less catchy
• GRAPHICS
• More subjective
• Interpretation needs
some experience
• More detailed information
• More catchy

5. • 22 year old female
• Tall, fair, good looking
• Cute smile with nice
dimples
• 36-24-36
• Flashy dressing style
Pictorial representations more informative
and attractive too!!!

6. MECHANICAL VENTILATION
Graphics
SCALARS LOOPS

7. COMPONENTS
• Scalars
– Any single variable plotted against time
– Flow Vs Time
– Volume Vs Time
– Pressure Vs Time
• Loops
– Two scalars plotted against each other
– Flow Vs Volume
– Pressure Vs Volume

8. SCALARS
Flow/Time
Pressure/Time
Volume/Time

9. Pressure-Volume Flow-Volume
LOOPS

10. FLOW Vs TIME CURVE
• General comments
– Time on the horizontal (x) axis and flow on
the vertical (y) axis
– Inspiratory flow above the base line and
expiratory flow below baseline
– Only scalar curve with significant tracing
below the baseline
• Normal depictions
– Differentiation of a mechanical Vs
spontaneous breath
– Recognition of the various patterns of
inspiratory flow in a mechanical breath
– Analysis of inspiratory and expiratory limbs
Vs

11. MECHANICAL Vs SPONTANEOUS
• Spontaneous inspiration
– sine flow pattern
• Mechanical breath
– inspiratory flow pattern depends on the pattern set
– can be square, accelerating, decelerating or sine
• Further differentiation can be made from
pressure time curve

12. MECHANICAL Vs SPONTANEOUS
Inspiration
Expiration
Spontaneous
Mechanical

13. INSPIRATORY LIMB
• Depicts the pattern of inspiratory
flow
– sine, square, decelerating or
accelerating
• Depicts the
– PIFR and
– inspiratory time

14. INSPIRATORY LIMB
Time (sec)
Flow
(L/min)
PIFR Inspiratory
Time
TI
Expiratory Time
TE

15. EXPIRATORY LIMB
• Depicts the PEFR and expiratory time
• PEFR is reached instantly and
expiratory flow ceases before the
expiration ends
• Expiratory flow pattern depends on
– Patient effort (active exhalation)
– Raw (bronchospasm, secretions etc)
– Elastic recoil of the lungs (compliance)

16. EXPIRATORY LIMB
Inspiration
Expiration
Time (sec)
Flow
(L/min)
Duration of
expiratory flow
Expiratory time
TE
PEFR

17. ABNORMALITIES IN F-T SCALAR
• Airflow obstruction
• Active exhalation
• Bronchodilator response
• Air trapping and auto PEEP
• Air leak

18. OBSTRUCTION Vs ACTIVE
EXPIRATION
• Obstruction
– Decreased PEFR which is attained
slightly later in expiration
– Duration of expiratory flow is prolonged
– Air trapping may be evident
• Active exhalation
– High PEFR and shortened duration of
expiratory flow

19. OBSTRUCTION Vs ACTIVE
EXPIRATION
Obstruction Active Expiration
Time
(sec)
Normal
Abnormal
Flow
(L/min)

20. BRONCHODILATOR RESPONSE
• Initial curve shows airflow
obstruction
• After bronchodilator administration
– PEFR and flow rates improve
– Duration of expiratory flow is shortened
– Air trapping, if present initially, is
abolished

21. BRONCHODILATOR RESPONSE
Before
Time (sec)
Flow
(L/min)
PEFR
After
Long TE
Higher
PEFR
Shorter TE

22. AIR TRAPPING AND AUTO PEEP
• Expiratory flow does not return
to baseline before the next
inspiration
• Auto PEEP results
– Flow time curve is very sensitive
to detect auto PEEP
– Does not display the magnitude
of auto PEEP
• Larger the distance from the
baseline, more is the auto
PEEP
0
+

23. AIR TRAPPING AND AUTO PEEP
Inspiration
Expiration
Normal
Patient
Time (sec)
Flow
(L/min)
Auto PEEP

24. VOLUME Vs TIME CURVE
• Time on the horizontal (x) axis and volume
on the vertical (y) axis
• Gives information about
– inspiratory and expiratory time
– inspiratory and expiratory tidal volumes
• Normally, the FRC is reached in expiration
much before the next inspiration begins
Vs

25. VOLUME Vs TIME GRAPH
Inspiration
Expiration
Time (sec)
Volume
(ml)
TI
Inspiratory Tidal Volume
TE

26. ABNORMALITIES
• Abnormalities that can
be identified include
– Active exhalation
– Air leak

27. ACTIVE EXHALATION
• Expiratory tracing of the
curve extends below the
baseline
• Another cause for a similar
appearance is poor
calibration of flow
transducer

28. ACTIVE EXHALATION
Volume (ml)
Time (sec)
Expiration

29. AIR LEAK
• Expiratory tracing does not
reach the baseline
– plateau after a smooth descent
• Volume of leak can be easily
measured from the graph

30. AIR LEAK
Volume
(ml)
Time (sec)
Air Leak

31. PRESSURE Vs TIME CURVE
• Time on the horizontal (x) axis and
pressure on the vertical (y) axis
• Differentiates mechanical from
spontaneous breath
• Differentiates controlled from
assisted breath
• Helps to identify various components
of inflation pressure
Vs

32. MECHANICAL Vs SPONTANEOUS
• For a spontaneous breath
– Inspiratory tracing is below baseline (negative)
– Magnitude of pressure swings are usually smaller
• For mechanical breath
– Both inspiratory and expiratory tracings are above
baseline

33. MECHANICAL Vs SPONTANEOUS
Mechanical
Time (sec)
Spontaneous
Paw
(cm H2O)
Inspiration
Expiration
Expiration
Inspiration

34. ASSISTED Vs CONTROLLED
• Assisted breaths
– Is triggered by patient
– Small initial negative deflection which indicates
patient effort
– Breaths may not occur at fixed intervals
• Controlled breaths
– Ventilator triggered – usually time triggered – breaths
occur at regular intervals
– No initial negative deflection

35. ASSISTED Vs CONTROLLED
Time (sec)
Assisted Controlled
Pressure

36. INFLATION PRESSURES
• Components include
– PIP – it is the maximum pressure
attained during inspiration
– PEEP – Identified when the curve does
not touch baseline
– P plateau – is a measure of the alveolar
pressure; measured by inspiratory
pause
– P ta – reflects the trans airway pressure
– difference of PIP and P plat

37. MECHANICAL BREATH
P
aw
(cm
H
2
O)
Time (sec)
PEEP
PIP

38. INSPIRATORY HOLD
• Ventilator gives us the option of holding breath in end
inspiration by pressing a button
• Possible/meaningful only in controlled mode with no
patient effort to inspire or expire
• This ceases airflow in full inspiration and the measured
airway pressure reflects alveolar pressure
• Alveolar pressure at end inspiration is a measure of
static lung compliance

39. INFLATION PRESSURES
Expiration begins
(Expiratory valve opens)
P
aw
(cm
H
2
O)
Time (sec)
PIP
Expiration
Inspiratory
Pause
P Plat
Transairway pressure (P ta)
Both valves closed

40. Begin Inspiration
Begin Expiration
P
aw
(cm
H
2
O)
Time (sec)
Distending
(Alveolar)
Pressure Expiration
Inflation Hold
(seconds)
PIP
WHAT DOES EACH SIGNIFY ?
P plat
P Plat reflects alveolar pressure – measure of elastic work
P ta reflects airway resistance – measure of resistive work

41. STATIC COMPLIANCE
• Static compliance (C st) = lung
volume at inspiratory hold divided
by pressure
• C st = Expiratory TV / (P plat –
PEEP)

42. ABNORMALITIES
• Increased airway resistance
• Decreased lung compliance
• High or inadequate inspiratory
flows

43. HIGH PEAK PRESSURES
• Can be due to
– Decreased lung compliance
– Increased airway resistance
– High inspiratory flow rates

44. INCREASED RESISTANCE Vs
DECREASED COMPLIANCE
INCREASED Raw
• Elevated PIP
• Normal P plat
• Elevated P ta
• Often, responds to
bronchodilators or
clearance of secretions
DECREASED Cst
• Elevated PIP
• Elevated P plat
• P ta normal or decreased
• Poor response

45. PIP Vs P plat IN VARIOUS STATES
Normal High Raw
High Flow
Low Compliance
Time (sec)
Paw
(cm
H
2
O)
PIP
PPlat
PIP
PIP PIP
PPlat
PPlat
PPlat

46. HIGH FLOW RATES
• Elevated PIP
• Normal P plat
• Elevated P ta
• Decreased inspiratory time (Ti) with supranormal
PIFR

47. PRESSURE VOLUME LOOP
• Pressure on the horizontal (X) axis and volume
on the vertical (Y) axis
• Gives information regarding
– Type of breath – mechanical Vs spontaneous
– Controlled Vs assisted mode
– Components of the PV loop – FRC, TV, PEEP PIP
and inflection points
– WOB – both elastic and resistive

48. COMPONENTS OF P-V LOOP
• Tracing begins from the FRC
• Application of PEEP
– increases the FRC level
– shifts tidal breathing to a higher segment of the lung volume
– rightward shift of the PV loop occurs
• PIP corresponds to the right extreme of the loop
• TV corresponds to the uppermost extreme of the loop

49. COMPONENTS OF P-V LOOP
Volume
(mL)
PIP
VT
Paw (cm H2O)

50. PEEP IN THE P-V LOOP
Volume
(mL)
VT
PIP
Paw (cm H2O)
PEEP

51. INFLECTION POINTS
• These are points of sudden change in slope of
the tracings
• Represent alveolar opening and recoil
– The lower inflection point indicates the beginning of
alveolar opening
– The upper inflection point indicates lung recoil and
over distention
• A higher LIP (shift of curve to right) indicates a
stiffer lung

52. INFLECTION POINTS
Pressure (cm H2O)
Volume (mL)
Upper Inflection Point
Lower Inflection Point

53. TYPE OF BREATH
• Mechanical breath
– Tracing is counter clockwise
– entire tracing is to the right of Y axis (pressure
remains positive throughout respiratory cycle)
• Assisted
– Tracing starts clockwise (patient trigger) and then
becomes counter clockwise
– Small negative deflection in pressure tracing (pt
trigger)
• Spontaneous
– Clockwise tracing
– inspiratory tracing on left side of Y axis (negative
intrathoracic inspiratory pressure)

54. PRESSURE VOLUME LOOP
Controlled Assisted Spontaneous
Vol
(ml)
Paw
(cm H2O)
I: Inspiration
E: Expiration
I
E
E
E
I
I

55. WORK OF BREATHING
A: Resistive Work
B: Elastic Work
Pressure (cm H2O)
Volume (ml)
B
A

56. ABNORMALITIES IN P-V LOOP
• Decreased lung compliance
• Increased airway resistance
• Overdistention
• Inadequate sensitivity
• Inadequate inspiratory flow
• Air leak

57. DECREASED COMPLIANCE
• Pattern slightly different in volume targeted and
pressure targeted modes
• Volume targeted
– Higher PIP needed for delivering same VT
– Shift of curve to right with widening
• Pressure targeted
– Lower VT delivered for same PIP
– Curve shifts downwards; slight narrowing

58. DECREASED COMPLIANCE
(Volume Targeted Ventilation)
Volume (mL)
PIP levels
Preset VT
Paw (cm H2O)
COMPLIANCE
Increased
Normal
Decreased

59. DECREASED COMPLIANCE
(Pressure Targeted Ventilation)
Volume (mL)
Preset PIP
V
T
levels
Paw (cm H2O)
COMPLIANCE
Increased
Normal
Decreased

60. INCREASED AIRWAY RESISTANCE
• Widening of the P-V loop
– Lower slope and increased Pta
• More evident in the inspiratory limb
• Termed increased hysteresis

61. INCREASED AIRWAY RESISTANCE
Pressure (cm H2O)
Higher PTA
Vol (mL)

62. OVERDISTENTION
• Increase in airway pressure without corresponding
increase in volume
– upper part of P-V loop becomes almost horizontal
• Called beak effect or Duckbill
• Commonly seen if ARDS or ILD patients ventilated in VC
mode with high VT
• Tackled by
– decreasing the set VT
– setting a lower alarm for PIP
– changing to PCV

63. OVERDISTENTION
Volume
(ml)
Pressure (cm H2O)
Normal
Abnormal
P aw rises
No rise in Vt

64. INADEQUATE SENSITIVITY
• Clinically significant as it increases the work to trigger
ventilatory assistance
– Negates the very purpose of ventilatory support
• Significant clockwise deflection occurs to the right of Y
axis
• Pressure decreases by >= 5 cm below the baseline
before ventilator delivers breath

65. INADEQUATE SENSITIVITY
Volume
(mL)
Paw (cm H2O)
Increased WOB

66. INADEQUATE INSPIRATORY FLOW
• P-V loop has a scooped out pattern
• Notching on the inspiratory limb
– may be evident if patient makes own
inspiratory attempts

67. INADEQUATE INSPIRATORY FLOW
Paw (cm H2O)
Volume
(ml)
Normal
Abnormal
Active Inspiration
Inappropriate Flow

68. AIR LEAK
• Expiratory limb of the P-V loop does not
reach the baseline (zero level)
• Magnitude of leak can be easily quantified

69. AIR LEAK
Volume (ml)
Pressure (cm H2O)
Air Leak

70. FLOW VOLUME LOOP
• Flow plotted on the vertical (y) axis and volume
on the horizontal (x) axis
• Inspiration plotted above the X axis and
expiration below it (can be opposite also)
• Gives information about
– PIFR
– PEFR
– Tidal volume

71. FLOW VOLUME LOOP
Volume (ml)
PEFR
Inspiration
Expiration
PIFR
VT

72. ABNORMALITIES
• Air leak
• Auto PEEP
• Increased airway resistance
• Airway secretions/condensate

73. AIRWAY SECRETIONS
• Flow volume loop tracing assumes a saw tooth
appearance
– Seen in the expiratory limb first
– If not promptly corrected, appears in inspiratory limb
also
• This feature has
– Positive predictive value of 94%
– Negative predictive value of 77% if absent

74. AIRWAY SECRETIONS
Inspiration
Expiration
Volume (ml)
Flow
(L/min)
Normal
Abnormal

75. INCREASED Raw
• Decreased expiratory flow rates – esp. – PEFR
• Expiratory tracing has a scooped out
appearance
• Tracing becomes slightly convex towards the
volume axis in early stages

76. INCREASED Raw
Inspiration
Expiration
Volume (ml)
Flow
(L/min)
Decreased PEFR
Normal
Abnormal
“Scooped out”
pattern

77. MODES OF VENTILATION
• Volume control / VC with assist
• Pressure control / PC with assist
• SIMV – volume and pressure targeted
• SIMV with PS
• SIMV with PS with CPAP
• PSV with and without CPAP
• Spontaneous breaths
• Dual modes

78. VOLUME CONTROL
Preset VT
Volume Cycling
Dependent on
CL & Raw
Time (sec)
Flow (L/m)
Pressure
(cm H2O)
Volume (mL)
Preset Peak Flow
Time triggered, Flow limited, Volume cycled Ventilation

79. ASSISTED VOLUME CONTROL
Time (sec)
Flow (L/m)
Pressure
(cm H2O)
Volume (mL)
Preset VT
Volume Cycling
Patient triggered, Flow limited, Volume cycled Ventilation

80. PRESSURE CONTROL
Pressure
Flow
Volume
(L/min)
(cm H2O)
(ml)
Time (sec)
Time-Cycled
Set PC level
Time Triggered, Pressure Limited, Time Cycled Ventilation

81. ASSISTED PRESSURE CONTROL
Pressure
Flow
Volume
(L/min)
(cm H2O)
(ml)
Set PC level
Time (sec)
Time-Cycled
Patient Triggered, Pressure Limited, Time Cycled Ventilation

82. PRESSURE SUPPORT
Time (sec)
Flow
(L/m)
Pressure
(cm H2O)
Volume
(mL)
Flow Cycling
Set PS
level
Patient Triggered, Flow Cycled, Pressure limited Mode

83. PSV WITH CPAP
Set PS level
CPAP level
Time (sec)
Flow
(L/m)
Pressure
(cm H2O)
Volume
(mL)
Flow Cycling

84. SIMV
(Volume-Targeted Ventilation)
Spontaneous Breaths
Flow
(L/m)
Pressure
(cm H2O)
Volume
(mL)

85. Pressure
Flow
Volume
(L/min)
(cm H2O)
(ml)
Set PC level
Time (sec)
SIMV Mode
(Pressure-Targeted Ventilation)
Spontaneous Breath

86. SIMV+PS
(Volume-Targeted Ventilation)
Flow
Pressure
Volume
(L/min)
(cm H2O)
(ml)
Set PS level
PS Breath
Flow-cycled

87. Pressure
Flow
Volume
(L/min)
(cm H2O)
(ml)
SIMV + PS
(Pressure-Targeted Ventilation)
PS Breath
Set PS level
Set PC level
Time (sec)
Time-Cycled Flow-Cycled

88. SIMV + PS + CPAP
(Volume-Targeted Ventilation)
Flow
Pressure
Volume
(L/min)
(cm H2O)
(ml)
Set PS level
CPAP level

89. Pressure
Flow
Volume
(L/min)
(cm H2O)
(ml)
Set PC level
Time (sec)
SIMV + PS + CPAP
(Pressure-Targeted Ventilation)
Set PS level
CPAP level

90. SPONTANEOUS BREATH
Time (sec)
Flow
(L/m)
Pressure
(cm H2O)
Volume
(mL)

91. CPAP
Time (sec)
CPAP level
Flow (L/m )
Pressure
(cm H2O)
Volume (mL)

92. ARDS ?
Useless ?
Too
complicated !!
How should
I proceed ?
What is
graphics ?