1. PATIENT-VENTILATOR
INTERACTION DURING PARTIAL
VENTILATORY ASSIST
Toshio Fukuoka
Dept Emergency and Intensive Care
Medicine, Nagoya University JAPAN
1!

2. Topics in my presentation
! Purpose of partial ventilatory support (PVA)
! Characteristics of PVA
! Unloading WOB (work of breathing) during
SIMV
! Patient-ventilator synchrony during PVA
! Several topics about PSV (pressure support
ventilation) and PAV (proportional assist
ventilation)
2!

3. Purpose of partial ventilatory
assist
! Achieve more comfortable assist for the
patient to avoid fighting and deep
sedation and/or neuromuscular blockade
! Keep respiratory muscle activity to
prevent the muscle atrophy during
ventilatory assist
! Unload the patient work of breathing
(WOB) during the weaning process
3!

4. Spontaneous breathing and
total ventilatory assist
Spontaneous breathing Total ventilatory assist
Airway pressure
Flow Pressure
provided by
Flow ventilator
Alveolar
pressure
Alveolar
pressure
Pmus
Pressure of patient
inspiratory muscle
4!

5. Partial ventilatory assist
(PVA)
Airway pressure
Pressure
provided by
Flow ventilator
Alveolar Synchrony and
pressure asynchrony
Pressure of patient
Pmus inspiratory muscle
5!

6. Modes of PVA
! Assist ventilation
! Synchronized intermittent mandatory
ventilation (SIMV)
! Pressure support ventilation (PSV)
! Proportional assist ventilation (PAV)
6!

7. Characteristics of PVA
methods
! Trigger
" When will the assist start?
! Frequency of support
" How many assist will be provided?
! Limit of support breath
" Does the assist have any limit or target of tidal
volume or airway pressure?
! Inspiratory-expiratory switching
" When will the assist stop for expiration?
7!

8. Assist (/control) ventilation
! Trigger: Patient inspiratory effort (PIE)
! Frequency: PIE
! Limit: Pre-set tidal volume
! Switching: Preset tidal volume (+pause
time)
8!

9. SIMV
! Trigger: Patient inspiratory effort (PIE)
! Frequency: Pre-set rate
! Limit: Pre-set tidal volume
! Switching: Preset tidal volume (+pause
time)
9!

10. PSV
! Trigger: Patient inspiratory effort (PIE)
! Frequency: PIE
! Limit: Pre-set airway pressure
! Switching: Inspiratory flow rate
10!

11. PAV
! Trigger: Patient inspiratory effort (PIE)
! Frequency: PIE
! Limit: Pre-set proportion of PIE in
pressure
! Switching: PIE (?)
11!

12. Characteristics of PVA
methods
Frequency Limit of
Trigger IE switching
of support support breath
Pre-set TV
ACV PIE PIE Pre-set TV
(+ pause time)
Time Pre-set Pre-set TV
IMV Pre-set TV
cycle frequency (+ pause time)
Pre-set Pre-set TV
SIMV PIE Pre-set TV
frequency (+ pause time)
Pre-set
PC-assist PIE PIE Pre-set time
pressure
Pre-set Pre-set
PC-SIMV PIE Pre-set time
frequency pressure
Pre-set
PSV PIE PIE Inspiratory flow
pressure
Pre-set ratio of
PAV PIE PIE PIE
PIE
12!

13. Unloading WOB during SIMV
! In 1970s, IMV and SIMV were introduced as
PVA and used widely for weaning process
from ventilator.
! Weaning by (S)IMV enables a gradual
reduction in the amount of support provided
by the ventilator and a progressive increase
in the amount of respiratory work performed
by the patient.
! But….
13!

14. Unloading WOB during SIMV
! Though SIMV showed gradual loading of
WOB during reduction of assist rate, one
study showed that even at 80% of support of
the minute ventilation, the ventilatory muscles
continue to perform significant work in patient
of ARDS. (Marini JJ et al ARRD 1988; 138: 1169)
! In SIMV, decreasing assist rate resulted in
increase WOB not only for the spontaneous
breaths, but also for the assisted breaths.
14!

15. EMG during SIMV
Assisted breaths and spontaneous breaths
Even at the assisted
breaths, EMG activity
was almost same as
spontaneous breaths.
Imsand C et al. Anesthesiology
1994; 80:13
15!

16. Unloading WOB during SIMV
! InSIMV, unloading WOB is far from
proportional to assist rate.
! Even if ventilator provide most of the
minute ventilation, level of WOB would
be enough to exhaust the patient.
16!

17. Clinical implication
Unloading WOB in SIMV
! Leaving an exhausted patient with SIMV with
spontaneous breaths might be a desperate
exercise for him/her rather than a rest.
! Check the patient condition to avoid
unintentional overload due to inappropriate
PVA.
" However even in PSV, a study showed that tidal
volume during the weaning was not a good
predictive factor for weaning success in COPD
patients.(Stroetz RW, Hubmayr RD. AJRCCM 1995;152: 1034)
17!

18. Asynchrony during PVA
! Frequency and limit
" Inadequate or excessive inspiratory flow or volume
! Trigger
" Trigger failure
" Trigger delay
" Auto-cycling
! IE Switching
" Premature termination
" Double triggering
18!

19. Asynchrony during PVA
! Frequency and limit
" Inadequate or excessive inspiratory flow or volume
! Trigger
" Trigger failure
" Trigger delay
" Auto-cycling
! IE Switching
" Premature termination
" Double triggering
19!

20. To match the ventilatory support
to patient inspiratory effort
! Matching the ventilator support to
patient inspiratory effort is a key of
patient-ventilator synchrony during PVA.
! Patient ventilatory pattern varies
significantly.
" However, sometimes patient ventilatory pattern is
not reliable.
20!

21. Tidal volume of spontaneous
breathing varies greatly.
JAMMES ET AL, BULLETIN EUROPEAN
DE PHYSIOPATHOLOGIE RESPIRATOIRE. 15: 527, 1979
In 235 healthy subjects, tidal volume (Vt) and respiratory rate
(fv) of varies so much.
21!

22. Mean tidal volume of the patients are
different and stable during PAV
In ventilator dependent
patients, tidal volume
was so constant with
Tidal volume(l)
different support level
of PAV.
Note: the difference in
tidal volume among the
patients
Assist levels of PAV(%)
MARANTZ ET AL, J. APPL. PHYSIOL 80: 397, 1996
22!

23. Fluctuation of ventilatory pattern
during ventilatory assist
Even in ventilator dependent patient, there is a breath-
by-breath variability in flow pattern.
Younes ARRD 1992
23!

24. Partial ventilatory assist
When the patient pulls differently, what would happen?
Airway pressure
Pressure
provided by
Flow ventilator
Alveolar Synchrony and
pressure asynchrony
Pressure of patient
Pmus inspiratory muscle
24!

25. Volume pre-set SIMV (or ACV)
Airway pressure
Pressure When Pmus
provided by
increases, ventilator
Flow ventilator
deliver the tidal
volume with preset
flow rate and airway
Alveolar pressure decrease.
pressure
Pull harder
Little push
Pressure of patient
Pmus inspiratory muscle
25!

26. Pressure support ventilation
Airway pressure
Pressure When Pmus
provided by
increases, ventilator
Flow ventilator
deliver more
inspiratory flow to
obtain the target
Alveolar pressure.
pressure
Pull harder
Same push
Pressure of patient
Pmus inspiratory muscle
26!

27. Proportional assist ventilation
When Pmus
Airway pressure increases, ventilator
Pressure
support level also
provided by
increases and
Flow ventilator
inspiratory flow rate
and airway pressure
increase.
Alveolar
pressure
Pull harder
More push
Pressure of patient
Pmus inspiratory muscle
27!

28. SIMV (ACV) PSV PAV
Pmus vs PIP and tidal volume
Inspiratory
Pmus ↑ Pmus ↓
time change
SIMV PIP:↓ PIP:↑
-
(ACV) VT:→ VT:→
PIP:→ PIP:→
PSV +
VT:↑ VT:↓
PIP:↑ PIP:↓
PAV +
VT:↑ VT:↓
PIP: peak inspiratory pressure, VT: tidal volume
28!

29. Synchrony during PVA
! PSV and PAV allow the inspiratory flow and
time to change in account of the patient
inspiratory effort during support breaths
! In PAV, airway pressure of support breaths
will change according to the patient
inspiratory effort.
" Though PAV has theoretical advantage over PSV,
SIMV and ACV in terms of patient-ventilator
synchrony, its efficacy and safety in clinical setting
should be evaluated more.
29!

30. Triggering synchrony
! Minimize the delay of trigger and trigger
failure
" Flow trigger or pressure trigger
" Avoid PEEPi and too-much-support
" Option: Other trigger signal for PVA?
• Esophageal pressure triggering?
# Adv: Free from effect of PEEPi
# Disadv: Noisy signal (heart beat and esophageal motion)
30!

31. Pressure trigger or flow trigger?
Flow triggering seemed to be better in terms of minimize
triggering PTP. NOTE: Difference between ventilator
types and trigger levels.
Aslanian P et al: AJRCCM 1998; 157: 135
31!

32. Pressure trigger or flow trigger?
! Though flow trigger seems to be better
than pressure trigger in terms of trigger
synchrony, type of ventilator and setting
of trigger level would be also important
to avoid trigger delay and asynchrony.
32!

33. Trigger failure due to (?) PVA
! PVA will cause PEEPi in 1) patients with
increase airway resistance, 2) tachypneic
patients and 3) small patients (premature
babies).
! To achieve trigger synchrony, decrease the
assist level is effective in some occasions.
! Several studies showed that in PAV the
trigger failure rarely occurred.
33!

34. Trigger failure (trigger
asynchrony) during assist
ventilation
*: trigger failure
The patient had severe airway obstruction.
Note: Expiratory flow at the start of inspiration.
Chao DC et al. Chest 1997; 112: 1592-1599
34!

35. PSV and PAV for tachypneic
RATE
patient
Pressure support level (cmH2O)
RATE
Younes, M.35!
1997
PAV assist level

36. Effect of reducing support
level to trigger failure
In PSV, triggering failure could be eliminated by
reducing support level.
Giannouli E et al. AJRCCM 1999; 159: 1716
36!

37. Clinical implication
! Decreasing respiratory rate in PVA
might be a sign of trigger failure.
! To avoid trigger failure, decrease the
ventilatory assist would be effective if
the patient is tolerable for the reduction.
! For avoid trigger failure, PAV showed
advantage in some studies.
37!

38. One more topic about PAV
! Decreasing mean airway pressure
without ABG worsening.
! PAV for small babies.
38!

39. Decrease in airway pressure
during PAV: clinical study
In cross over trial of 8
septic patients, during
PAV, PIP was decreased
significantly and cardiac
output increased
significantly comparing
with in ACV.
Younes, M 1992.
39!

40. Decrease in mean airway
pressure during PAV
! In cross-over trial of premature babies, PAV
successfully reduced mean airway pressure
without ABG worsening comparing with
conventional mechanical ventilation.
(Schulze, A et al. J Pediatr 1999)
" Decrease in mean airway pressure might prevent
barotrauma and BPD in ventilated premature
babies (no clinical trial for this endpoint is available
now).
40!

41. Summary
! Characteristics of PVA
" Trigger, Frequency, Limit, Switching
! Unloading WOB in SIMV
" Watch your patient. Do not rely on the assist rate.
! Synchrony during PVA
" Flow trigger > pressure trigger (?)
" (PAV) > PSV > SIMV/ACV
" Decrease the respiratory rate during PVA? Then
check patient breath rate, or you might miss the
asynchrony.
! PAV: Promising PVA. Use it with caution today.
41!

42. 42!