VENTILATOR ASYNCHRONY pathophysiology and clinical relevance

1. VENTILATOR
ASYNCHRONY
PATHOPHYSIOLOGY AND CLINICAL RELAVANCE

2. Main purpose ventilator is to decrease work of breathing
What is work of breathing ?
 Respiratory muscles account for 1% - 3% of total oxygen consumption
 In patients with acute hypoxemic respiratory failure and shock who are
undergoing cardiopulmonary resuscitation the respiratory muscles account
for approximately 20% of total oxygen consumption
 This result in increased work of breathing

3. Before entering in
ventilator asynchrony let us just
recall about ventilatory graphics

4. Mechanical Ventilation
Graphics
SCALARS LOOPS

5. SCALARS
Flow/Time
Pressure/Time
Volume/Time

6. Pressure-Volume Flow-Volume
LOOPS

7. SCALARS
Flow/Time Pressure/Time
Volume/Time

8. Spontaneous Breath
Time (sec)
Flow
(L/min)
Inspiration
Expiration

9. Mechanical Breath
Inspiration
Expiration
Flow
(L/min)
Time (sec)

10. Typical Flow Patterns
ACCELERATING
DECELERATING
SINE
SQUARE

11. Inspiratory Flow Pattern
Inspiration
Expiration
Time (sec)
Flow
(L/min)
Beginning of inspiration
exhalation valve closes
Peak inspiratory flow rate
PIFR
Beginning of expiration
exhalation valve opens
Total cycle time
TCT
Insp. time
TI
Expiratory Time
TE

12. Expiratory Flow Pattern
Inspiration
Expiration
Time (sec)
Flow
(L/min)
Beginning of expiration
exhalation valve opens
Peak Expiratory Flow Rate
PEFR
Duration of
expiratory flow
Expiratory time
TE

13. Inadequate Inspiratory Flow
Flow
(L/min)
Time (sec)
Normal
Abnormal
Active Inspiration or Asynchrony
Patient’s effort

14. Obstruction vs Active Expiration
Obstruction Active Expiration
Time
(sec)
Normal
Abnormal
Flow
(L/min)

15. Air Trapping
Inspiration
Expiration
Normal
Patient
Time (sec)
Flow
(L/min)
Air Trapping
Auto-PEEP
}

16. SCALARS
Flow/Time
Pressure/Time
Volume/Time

17. Volume vs Time
Inspiration
Expiration
Time (sec)
Volume
(ml)
Inspiratory Tidal Volume
TI

18. Air Leak
Volume
(ml)
Time (sec)
Air Leak

19. Active Exhalation
Volume (ml)
Time (sec)

20. SCALARS
Flow/Time
Pressure/Time
Volume/Time

21. Spontaneous Breath
P
aw
(cm
H
2
0)
Time (sec)
Inspiration
Expiration

22. Mechanical Breath
Inspiration
Expiration
P
aw
(cm
H
2
O)
Time (sec)
}
TI
Peak Inspiratory Pressure
PIP
PEEP
TE

23. Mechanical
Time (sec)
P
aw
(cm
H
2
O)
Time Triggered Breath
CONTROLLED BREATH
(Time Triggered)

24. Assisted Breath
(Patient Triggered)
Mechanical
Time (sec)
P
aw
(cm
H
2
O)
Patient Triggered Breath

25. Assisted vs Controlled
Assisted Controlled
Pressure
(cmH20)
Time (sec)

26. Spontaneous vs. Mechanical
Mechanical
Time (sec)
Spontaneous
Paw
(cm H2O)
Inspiration
Expiration
Expiration
Inspiration

27. Components of
Inflation Pressure
Begin Expiration
P
aw
(cm
H
2
O)
Time (sec)
Begin Inspiration
PIP
Pplateau
(Palveolar)
Transairway Pressure (PTA)
} Exhalation Valve Opens
Expiration
Inspiratory Pause

28. Begin Inspiration
Begin Expiration
P
aw
(cm
H
2
O)
Time (sec)
Distending
(Alveolar)
Pressure Expiration
Inflation Hold
(seconds)
Begin Expiration
P
aw
(cm
H
2
O)
Time (sec)
Begin Inspiration
PIP
Pplateau
(Palveolar
Transairway Pressure (PTA)
} Exhalation Valve Opens
Expiration
PIP

29. PIP vs Pplat
Normal High Raw
High Flow Low Compliance
Time (sec)
Paw
(cm
H
2
O)
PIP
PPlat
PIP
PIP PIP
PPlat
PPlat
PPlat

30. Paw
(cm
H
2
O)
Normal
Normal PPlat
(Normal Compliance)
Increased PIP
} Increased PTA
(increased Airway Resistance)
Normal
PIP
PPlat
High Raw
PIP
PPlat
Increased Airway Resistance

31. DECREASED COMPLIANCE
Time (sec)
Paw
(cm
H
2
O)
Low Compliance
PIP
PPlat
Normal
PIP
PPlat
Normal PPlat
(Normal Compliance)
Increased PPlat
(Decreased Compliance)
Normal
PIP

32. Pressure-Volume Flow-Volume
LOOPS

33. Pressure-Volume Loop
(Type of Breath)
Controlled Assisted Spontaneous
Vol
(ml)
Paw
(cm H2O)
I: Inspiration
E: Expiration
I
E
E
E
I
I

34. Pressure-Volume Flow-Volume
LOOPS

35. Flow-Volume Loop
Volume (ml)
PEFR
FRC
Inspiration
Expiration
PIFR
VT

36. Air Leak
Inspiration
Expiration
Volume (ml)
Flow
(L/min)
Air Leak in mL
Normal
Abnormal

37. Air Trapping
Inspiration
Expiration
Volume (ml)
Flow
(L/min)
Does not return
to baseline
Normal
Abnormal

38. Increased Airway Resistance
Inspiration
Expiration
Volume (ml)
Flow
(L/min)
Decreased
PEFR
Normal
Abnormal
“Scooped out”
pattern

39. Airway Secretions/
Water in the Circuit
Inspiration
Expiration
Volume (ml)
Flow
(L/min)
Normal
Abnormal

40. PATIENT -VENTILATOR ASYNCHRONY
 Synchronous ventilation occurs when the ventilator responds
appropriately to a patients inspiratory effort and delivers the amount
of flow and requested by the patient
 Asynchrony occurs when the patient inspiratory efforts and flow
demands are not accomaated by the ventilator
 Asynchrony may also accompanied by Tachypnea, chest wall
retractions and chest-abdominal paradox

42. TRIGGER
• Ineffective
• Double
• Reverse
• Auto
FLOW
• Insufficient
flow
• Excess flow
CYCLE
• Premature
• Delayed

43. TRIGGER ASYNCHRONY
 Trigger asynchrony occurs when the ventilator sensitivity settings is not
appropriate for the patient, with this type of asynchrony ventilator does not
sense the patients inspiratory effort and fails to deliver the gas flow
 Trigger that is too insensitive requires the patient to make a strong,
spontaneous effort to achieve gas flow from the ventilator
 In a patient with spontaneous breathing effort, If pressure triggering is being
used, a change to flow triggering may help because flow triggering generally
reduces inspiratory WOB.

44. TYPES OF TRIGGER ASYNCHRONY
 Ineffective efforts
Trigger delay
Double
Reverse
Auto

45. Ineffective Efforts
 Ineffective effort is defined as a patient’s effort being unable to trigger the
ventilator breath.
 the ventilator is unable to detect the patient’s neural effort despite the presence of
an inspiratory effort
 From a clinical point of view, ineffective effort can be detected by analyzing the
breathing frequency shown on the ventilator monitoring system that is lower than
the breathing frequency monitored by observing the patient’s chest/abdomen
movements.

47. Cause of Asynchrony
1. Low trigger sensitivity
2. Weak respiratory drive or weak effort secondary to heavy sedation, excessive
respiratory support, or diaphragm dysfunction
3. Presence of high threshold load such as intrinsic PEEP
4. Delayed cycling, especially in PSV mode or obstructive condition or during
NIV in presence of intentional leak in a ventilator unable to compensate for
them

48. Solution of Asynchrony
 Adjust trigger sensitivity,
 reduce sedation or use drugs with no effect on the respiratory drive,
 increase PEEP to counter intrinsic PEEP,
 shorten inspiratory time,

49. Delayed triggering
• Triggering delay is a time lag between the onset of the patient’s effort and the
onset of ventilator pressurization. This is a typical asynchrony between the
respiratory drive and the inspiratory trigger
• A time lag of > 100ms between the onset of patient effort and the onset of flow
delivered by the ventilator

50. Delay between the
beginning of
inspiratory effort
and the triggering

51. Cause of Asynchrony
o low trigger sensitivity
o Low respiratory drive
o Presence of a partially obstructed ETT or HME
Solution of Asynchrony
 Adjust trigger sensitivity,
 Decrease inspiratory time and increase expiratory time
 Reduction of minute ventilation by lowering assist (decrease set pressure, set VTe)
 increase PEEP to counter intrinsic PEEP,
 replace HME or ETT, change NIV interface

52. Auto triggering
 Auto-triggering is a mechanical breath that is not triggered by the patient’s
inspiratory effort beyond the mandatory breaths
 It is an asynchrony between the respiratory drive and the
inspiratory trigger.

53. Auto-triggering caused by leak
in the circuit. Note that there is
no drop of the airway pressure
in the pressure/time waveform
(Upper waveform) at the
beginning of the inspiratory
phase which means that the
breaths are not patient trigger

54. Cause of Asynchrony
 High trigger sensitivity
 Leaks
 Random noise in the circuit (eg, cardiac oscillations,condensed water in the
ventilator circuit, copious tracheobronchial secretions)
Solution of Asynchrony
 Adjust trigger sensitivity
 Check for leaks in circuit
 Remove condensed water from the trap
 Auscultate and check for secretions
 Inflate ETT cuff

55. Double triggering
 Double-triggering, also called double-cycling or breathstacking, consists
of 2 breaths that may or may not be separated by a very short
expiratory time.
 Occurrence of 2 consecutive breaths with an interval of less than half of
the mean inspiratory time (TI).

56. Red arrow show double-
triggering in the
pressure/time waveform.
White arrow show double-
triggering in the flow/time
waveform

57. Cause of Asynchrony
 Respiratory drive is high
 Delivered ventilatory support is insufficient (eg, tidal volume [VT] or V
̇ E too
low)
 Neural TI is longer than the TI set on the ventilator
Solution of Asynchrony
 Increase inspiratory time
 Modes that allow variation in tidal volume, such as PCV
 Decrease the cycling threshold percentage (PSV)
 Patient factor-Correct underlying fever, anxiety

58. Reverse triggering
 Reverse-triggering is a type of asynchrony that happens when a
patient’s effort occurs after the initiation of a ventilator breath (ie, a
breath not triggered by the patient).
Cause of Asynchrony
 Occurs mainly in patients who are deeply sedated
 Over assistance
 Prolonged NMB

59. White arrows show
reverse triggering in the
pressure/time waveform

60. Solution of Asynchrony
 No single effective treatment strategy.
 Reducing RR to increase patient triggered breaths.
 Reducing sedation and awakening the patient
 Neuromuscular Paralysis

61. Flow asynchrony
 Flow asynchrony occurs when the patient’s flow demand is not met by the
ventilator. The type of mode being used often determines how much flow is
available
 During volume control ventilation, if flow is constant, the set flow may not match
patient demand. This is a fairly common problem . An initial flow of 80 L/min is
typically suggested. In this situation the best way to determine if adequate flow is
being provided is to evaluate the pressure–time scalar. When the pressure curve
appearance changes from breath to breath, the patient is actively breathing. A
concave appearance on the inspiratory pressure curve during volume control
ventilation indicates active inspiration

62.  During pressure-targeted ventilation, such as PC-CMV and PSV, the
ventilator rapidly provides a high flow to achieve and maintain the
set pressure. As long as the set pressure is adequate, flow to the
patient will be adequate

63. Breath a is a control breath
with no patient effort. Breath
b is a patient-triggered breath
with adequate flow. The
dotted line mimics a passive
breath as in a. Breath c is a
patient-triggered breath with
inadequate flow to meet
patient demand (solidline).

64. TYPES OF FLOW ASYNCHRONY
 Insufficient flow
 Excess flow

65. Insufficient flow
Determining factor Therapeutic strategy
Ventilator :
• In VCV, the flow setting is
too low
• In PCV and PSV  the
applied pressure is too low,
long rise time
• In VCV, increase inspiratory
flow
• PCV or PSV increase
pressure support

66.  Excessive ventilator
demand, increased
neural drive
 Reduce neural drive and
metabolic demand.
 control fever, pain,
metabolic acidosis and
anxiety.
Patient factors :

68. Excess flow
Determining factor Therapeutic strategy
 In VCV, the flow setting is
too high
 In VCV, decrease inspiratory
flow
 In PCV and PSV, the applied
pressure is too high, rise time
is too short
 In PCV and PSV, decrease
applied pressure, increase
rise time

69. severe overshoot
causing dramatic
pressure spikes

70. Cycle asynchrony
 Cycle asynchrony, also called termination asynchrony, usually occurs when the
patient starts to exhale before the ventilator has completed inspiration.
 Cycle asynchrony often occurs when TI is too long. Increasing the flow in volume
control ventilation to shorten TI, - decreasing the set TI time in volume control or
pressure control may help.
 Cycle asynchrony can occur with both mechanical (mandatory) and spontaneous
breaths. During spontaneous ventilation with PSV, cycle asynchrony commonly
occurs when the patient actively tries to exhale before the expiratory flow
termination

71. TYPES OF CYCLE ASYNCHRONY
 Premature cycling
 Delayed cycling

72. Premature cycling
Determining factor Therapeutic strategy
 Inspiratory time is too short relative
to patient inspiratory time
 Low level of assist
 In VCV, decrease inspiratory flow
or increase tidal volume or add end
inspiratory pause
 In PCV, increase inspiratory time.
.

73. Example of premature cycling.
White arrows show an
inspiratory effort that continues
after the inspiratory phase
ended in the pressure/ time
waveform.
Red arrows show a sudden
change in the expiratory flow
caused by the inspiratory effort
of the patient

74. Delayed cycling
 Ventilator breath cycle is longer than the patient’s inspiratory time.

75. Determining factor Therapeutic strategy
 Inspiratory time > patient
inspiratory time
 Excessive tidal volume , long I
time
 In VCV, decrease in Vt(will dec I
time)
 In PCV, decrease inspiratory
time.
 Bronchodilator, steroid therapy,
aspiration of secretions.