1. Patient – Ventilator Asynchrony
Dr Vincent Ioos
Medical ICU – PIMS
APICON 2008
Workshop on Mechanical Ventilation

2. Goal of mechanical ventilation
Do you mechanically ventilate your patient to reverse diaphragmatic fatigue ? or
Do you encourage greater diaphragm use to avoid ventilator-induced diaphragmatic dysfunction?

4. Patient triggered ventilation
Assisted mechanical ventilation
Avoid ventilator induced diaphragmatic dysfunction
Providing sufficient level of ventilatory support to reduce patient’s work of breathing

6. Volume or pressure oriented?

7. Volume oriented modes Inspiratory flow is preset
Inspiratory time determines the Vt
The variable parameter is the airway peak and plateau pressure

8. Equation of insuflated gases in flow assist control ventilation
Describes interactions between the patient and the ventilator
Pressure required to deliver a volume of gas in the lungs is determined by elastic and resistive properties of the lung
Paw = Vt/C +VR + PEP

9. C = Vt / P and P = P Plat - PEEP
Airway Pressure
Paw= Po + Vt/C + RV
C = Vt / P and P = P Plat - PEEP

10. Flow shapes

11. Pressure oriented modes
Pressure in airway is the preset parameter
Flow is adjusted at every moment to reach the preset pressure
The variable parameter is Vt

12. Equation of motion in pressure support ventilation
Paw + Pmus = Vt/C + VxR + PEP
Pressure = pressure applied by the ventilator on the airway + pressure generated by respiratory muscles
Pmus is determined by respiratory drive and respiratory muscle strenght

13. Determinant factors of inspiratory flow in PSV
Pressure support setting
Pmus (inspiratory effort)
Airway resistance
Respiratory system compliance
Vt directly depends on inspiratory flow, but also on auto-PEEP (decreases the driving pressure gradient)

15. Look at the curves !

16. A challenge for the intensivist
Discomfort anxiety
Increased work of breathing
Increased requirement of sedation
Increased length of mechanical ventilation
Increased incidence of VAP 

17. Patient-ventilator asynchrony
Mechanical ventilation: 2 pumps
Ventilator controlled by the physician
Patient’s own respiratory muscle pump
Mismatch between the patient and the ventilator inspiratory and expiratory time time
Patient « fighting » with the ventilator

20. Ventilation phases

21. Trigger asynchrony
Ineffective triggerring: muscular effort without ventilator trigger
Double triggerring
Auto-triggering
Insensitive trigger: triggering that requires excessive patient effort

22. Ineffective triggering

24. Double triggering
Cough
Sighs
Inedaquate flow delivery

25. Auto-triggering Circuit leak Water in the circuit Cardiac oscillations
Nebulizer treatments
Negative suction applied trough chest tube

28. Flow asynchrony Fixed flow pattern (volume oriented)
Variable flow pattern (pressure oriented)

29. Volume oriented ventilation (fixed flow pattern)
Inspiratory flow varies according to the underlying condition
If patient’s flow demand increases, peak flow should be adjusted accordingly
Usually, peak flow is too low
Dished-out appearance of the presure-wave-form
Importance of flow-pattern

31. Ineffictive triggering at 30 l/mn
Increase in flow rate
Subsequent increase of expiratory time
Decreased dynamic hyperinflation
Subsequent decrease in ineffictive trigerring

32. Importance of flow pattern
Increase in peak-flow setting fron 60 to 120 l/mn eliminated scooped appearance of the airway pressure waveform

33. Pressure oriented ventilation (variable flow)
Peak flow is depending on :
Set target pressure
Patient effort
Respiratory system compliance
Adjustement : rate of valve opening = rise time = presure slope = flow acceleration

37. Termination asynchrony
Ventilator should cycle at the end of the neural inspiration time
Delayed termination:
Dynamic hyperinflation
Trigger delay
Ineffective triggering
Premature termination

40. Set inspiratory time < 1 sec

41. PSV = 10 cmH2O Patient 1 Patient 2
Inspiratoy flow terminate despite continued Pes defelection
Double Trigerring

42. Expiratory asynchrony
Shortened expiratory time:
Auto-PEEP  trigger asynchrony
Delay in the relaxation of the expiratory muscle activity prior to the next mechanical inspiration
Overlap between expiratory and insiratory uscle activity
Prolonged expiratory time

43. Auto-PEEP created by flow patterns that increases inspiratory time
Lower peak flow during control ventilation
Switch from constant flow to descending ramp flow
Inadequate pressure slope during presure controlled ventilation
Termination criteria that prolong expiratory time during PSV

47. Conclusion Look at your patient ! Look at the curves !
Have a good knowledge of the ventilation modalities of the ventilator you are using
Excessive ventilatory support leads to ineffective triggering
Do not forget to set trigger sensitivity, to avoid excessive effort and auto-triggering