1. How to choose optimal settings
Decision taking
Mechanical Ventilation
Patient
Equipment
Peter C. Rimensberger
Pediatric and Neonatal ICU
Department of Pediatrics
University Hospital of Geneva
Geneva, Switzerland

2. Defined Clinical Targets and Goals
1) Achieve good oxygenation and acceptable CO2
2) reduce WOB in spontaneous breathing patients
limit peak pressure
use lower Vt
use higher PEEP
3) Try to protect the lung
limit peak pressure
use lower Vt
use higher PEEP

3. ARDS network trial (6 vs.12 ml/kg)
Small Vt ventilation
ARDS network trial (6 vs.12 ml/kg)
n = 861
Mortality: 31 vs. 38
(p < 0.007)
PIP: 32 vs. 39 cmH2O
Pplat: 25 vs. 33 cmH2O
NEJM 2000;342:

4. Have changes in ventilation practice improved outcomes ?
Albuali WH Pediatr Crit Care Med 2007; 8:324 –330

5. Clinical variables associated with mortality
Multivariate
analysis
Albuali WH
PCCM 2007; 8:324 –330

6. Max. used Vt and effect on the developpment of ALI in ICU patients without lung injury50 40 30 20 10
Mean Vt 10.9 ± 2.3
p < 0.001
n = 100
Proportion of ALI (%)
n = 160
n = 66
< 9
9 to 12
> 12
Tidal Volume (ml/kg PDW)
Gajic O et al. Crit Care Med 2004; 32:
Physiologic Vt (normal lungs with spont. breathing) : 6 to 7 ml/kg

7. The concept of small Vt ventilation is a concept of “physiologic Vt ventilation”
ARDS network trial (Vt 6 vs. 12 ml/kg)
n = 861
Mortality: 31 vs. 38
(p < 0.007)
NEJM 2000;342:
Physiologic Vt (normal lungs with spont. breathing) : 6 to 7 ml/kg

8. … and in the neonate?
… no RCT in newborn infants has substantiated so far the experimental finding that avoiding large tidal volumes … is lung protective in newborn infants.

9. NeoVent Ventilation practices in the neonatal intensive care unit: an international cross-sectional study
Van Kaam A , Rimensberger PC (manuscript submitted)

10. NeoVent Ventilation practices in the neonatal intensive care unit: an international cross-sectional study
Van Kaam A , Rimensberger PC (manuscript submitted)

11. The ARDS lung is rather small than stiff
The baby lung
The ARDS lung is small, with a normal aerated portion having the dimension of the lung of a 5- to 6- year old child (200 – 300 g of lung tissue as compared to 700 g)
Gattinoni L Intensive Care Crit Dig 1987; 6:1-4
Gattinoni L et al. J Thorac Imaging 1988; 3:59-64
= percentage of the expected normal lung volume
The ARDS lung is rather small than stiff

12. 1) Adult and child: Acute respiratory distress syndrome (ARDS)
ARDS is a heterogeneous lung disease
2) Neonate: (Infant) Respiratory distress syndrome (iRDS)
iRDS is a heterogeneous lung disease

13. MRI signal intensity from non-dependent to dependent regions
The water burden of the lung makes the lung of the preterm infant,
despite surfactant treatment, vulnerable to VILI
4-day-old, 26-week gestation infant
2-day-old, 38-week gestation infant
Adams EW AJRCCM 2002; 166:397–402

14. The baby lung. The ARDS lung is small, with a normal
The baby lung The ARDS lung is small, with a normal portion having the dimension of the lung of a 5- to 6- year old child (200 – 300 g of lung tissue as compared to 700 g)
Gattinoni L, Pesenti A Intensive Care Crit Dig 1987; 6:1-4
Airway pressure (cmH2O)
Volume (l)
The normal lung
The
baby
lung
Vt / kg ratio
Vt / “baby lung” ratio
Overdistention

15.  “permissive hypercapnia”, HFOV, ECMO or ECCO2-R
Allowable Vt depends on pathology and disease severity
The normal lung
Volume (l)
or pathologies with reduced TLC:
- Lung hypoplasia
CDH
iRDS
- Lobar Collapse
- Lobar Pneumonia
The
baby
lung
Airway pressure (cmH2O)
Vt of 6 ml/kg bw in a patient with a by 50% reduced TLC corresponds to at Vt of 12 “ml/kg”, he should therefore receive only 3 ml/kg bw !
 “permissive hypercapnia”, HFOV, ECMO or ECCO2-R

16. ARDS network trial (6 vs.12 ml/kg)
Higher PEEP
during small Vt ventilation or peak pressure limitation
ARDS network trial (6 vs.12 ml/kg)
n = 861
Mortality: 31 vs. 38
(p < 0.007)
PIP: 32 vs. 39 cmH2O
Pplat: 25 vs. 33 cmH2O
NEJM 2000;342:
Oxygenation target

17. PEEP and FiO2 allowances in PEEP studies
ARDS Network 6 versus 12 ml/kg: NEJM 2000;342:
ALVEOLI: NEJM 2004;351:
LOVES: Meade MO ;299(6):

20. CT-aeration At ZEEP and 2 PEEP levels = turning up the PEEP approach
poorly areated
normal
CT-aeration
At ZEEP and
2 PEEP levels
= turning up
the PEEP
approach
Diffuse CT-attenuations
Focal CT-attenuations
Rouby JJ AJRCCM
2002;165:1182-6

21. “Anatomical” Recruitment
Recruit to TLC (?)
Gattinoni L
AJRCCM 2001; 164:1701
Focus is on “opening” (re-aerating) previously collapsed lung units

24. The PEEP step approach: “Functional” Recruitment
25/10
Overinflation ends
Pressure control ventilation
PEEP 15
PEEP 20
PEEP 10
PEEP 25
40/25
Over-
inflation
starts
Rimensberger 2000 (unpublished)
Focus is on “opening”, but certainly on avoiding overdistending lung units
P/F-ratio, oxygen delivery and quasi-static Crs during PEEP steps
Lichtwarck-Aschoff M AJRCCM 2000; 182:

25. O2-improvement = Shunt improvement =
a) recruitment
PaO2
PaCO2 VA
b) flow diversion
PaO2 VA
PaCO2
Gattinoni L (2003)

26. Prevalent overinflation = dead space effect
PEEP 15 1 2 1 –
PEEP
PaO2 and PaCO2 increase
Gattinoni L (2003)

27. PEEP titration: O2 and CO2 response
Steps of 5 cmH2O to 40/25
Pressure control ventilation
25/10
25/10
Overinflation ends
PEEP 25
PEEP 20
PEEP 15
PEEP 10
Overinflation starts

28. Understanding lung opening and closing
Behavior of the whole lung: Hysteresis
Behavior of a single alveolus
Radford: in Respiratory Physiology (eds. Rahn and Fenn) 20 19

29. Lung opening and closing
Frequency distribution of opening and closing pressure in patients with ARDS
Crotti S AJRCCM 2001;164: 131–140
Behavior of the whole lung: Hysteresis
Volume derecruitment throughout deflation
UIPdefl
Pclosing
Alveolar recruitment throughout inflation
LIP
UIPinfl
Radford: in Respiratory Physiology (eds. Rahn and Fenn) 20 19

30. Rimensberger PC Crit Care Med 1999; 27:1946-5240
Pressure (cmH2O)
Volume
Intrigued by this basic physiologic observation we wanted to know what was now happening in such a lung that exhibits hysteresis during mechanical ventilation.
First we generated in a rabbit with surfactant depleted lungs a quasi-static pressure-volume by by stepwise insufflation and desufflation of fixed volume aliquots. Then we repeated this maneuver imitating mechanical ventilation going up to 15, 20, or 25 cmH2O respectively and desufflated from this different pressure points (corresponding to the peak pressure during ventilation). You can observe, that by increasing the maximal insufflation pressure volumes increased on the volume axes with a deflation limb moving upwards, which means recruitment of lung volumes.
In a next step we did a similar thing but going first to 3o cmH2O, corresponding to total lung capacity) and desufflated to 15, 10, and 5 cmH2O, repsectively, fllowed by a reinsufflation from these various pressure points that correspond to PEEP during ventilation.
Pressure (cmH2O)
Rimensberger PC Crit Care Med 1999; 27:

31. small tidal volume ventilation (5 ml/kg)30
Pression
Optimal PEEP
Recruited vol 8
Lung recruitment allows to place the respiratory cycle on the deflation limb
And this again allows then to explore the pressure-volume relationship of the lung to position the dynamic cycle in almost every place desired. Using small VT and a PEEP of 8 in this situation first, followed by a short increase to 30 cmH2O of airway pressures as a sustained inflation and reducing then again the PEEP to 8 as previously led to a gain on lung volumes with the tidal cycle now on the deflation limb. Note that we are now on a more compliant part of the curve.
Rimensberger PC Crit Care Med 1999; 27:

32. Oxygenation response in two groups; with and without recruitment (identical PEEP)
optimal-PEEP
recruited vol.
Gradient PaO2/FiO2
This maneuver improves oxygenation...
Rimensberger PC Crit Care Med 1999; 27: 25

33. Lung recruitment: The optimal least PEEP approach
optimal-PEEP
recruited vol.
Rimensberger PC
Crit Care Med 1999; 27:
Rimensberger PC
Crit Care Med 1999; 27:1940-5 25

34. This slide illustrates the effect of a single recruitment maneuver on lung volumes in a baby on ECMO for congenital diaphragmatic hernia.

35. The open lung concept searches for maintaining lung volume
before RM
after RM
Halter JM AJRCCM 2003, 167:1620-6
alveoli per field
inspiration
expiration
I – E
PEEP before and after
Rimensberger PC Crit Care Med 1999; 27:1946

36. Keep PEEP after RM above lung closing
PEEP is an expiratory phenomenon to maintain the lung open
Keep PEEP after RM above lung closing
Rimensberger PC
Crit Care Med 1999; 27:
Lapinsky SE Intensive Care Med 1999; 25:

37. Optimal = “Maximum dynamic compliance and best oxygenation at the least pressure required”
So we could develop a strategy to position the tidal cycle optimally in the safe window, at the point of maximum dynamic compliance, at the least pressure required, which will result in good oxygentaton. This is illustrated in this mathematical lung model from Keith Hickling
Hickling KG et al. AJRCCM 2001; 163:69-78

38. Volume Pressure TLC UIP CCP LIP Courtesy from David Tingay
Lachmann and colleagues through their ‘OPEN LUNG CONCEPT’ work have described a technique in which ventilation can be applied near the top of the deflation limb of the pressure volume relationship. Lachmann utilises the relationship between lung volume and oxygenation to achieve this.
Their technique involves incremental increases in mean airway pressure MOUSE CLICK, which recruits lung volume, until the best oxygenation is achieved. They have shown that this point should be close to Total Lung Capacity and any further increases in mean airway pressure will result in overdistension of the lung and impairment of oxygenation. As the lung is now recruited and because the lung displays hysteresis if mean airway pressure is decreased any resultant change in lung volume should occur near the deflation limb. Initially this will result in small changes in lung volume until the critical closing pressure of the lung is reached and subsequently any further decrease in mean airway pressure will result in rapid loss of lung volume, with resultant drop in oxygenation.
Pressure
Courtesy from David Tingay
Royal Children’s Hospital Melbourne 38

39. Use of dynamic compliance for open lung positive end-expiratory pressure titration in an experimental study
F Suarez-Sipman
Crit Care Med 2007; 35:214–221

40. Get the lung as much homogeneous as possible
Frerichs I et al. J Appl Physiol 2002; 93: 660–666
Volume
distribution
Frerichs I, Dargaville P, Rimensberger PC Intensive Care Med 2003; 29:2312-6

41. Volume distribution Tidal volume distribution
Frerichs I, Dargaville P, Rimensberger PC Intensive Care Med 2003

42. Regional «homogeneity» on the deflation limb
right lung non-dependent region
normal lung
injured lung
post surfactant lung
right lung dependent region
normal lung
injured lung
post surfactant lung
Dargaville P, Frerichs I, Rimensberger PC (submitted)

43.  similar time constants
ARDS / RDS lung
(Heterogeneous)
Alveolar
Rupture!
C = 2
Vt=3ml/kg
 similar time constants
homogeneous
Vt distribution
Normal lung / recruited lung
at optimal lung volumes
Vt=6ml/kg
C = 2
Vt=5ml/kg
Vt=6ml/kg
C = 1
VT= 1ml/kg
 various time constants
Very compliant healthy lung adjacent to noncomliant ARDS lung depicted by thickened wall
 heterogeneous
Vt distribution

44. Heterogeneous: Injured Lung
Contrast this to the heterogeneously injured lung. On alveoli is collapsed and there is loss of interdependece. The remaining alveoli fill the void as they over- expand which is no longer buffered by the 4th alveoli. Unstable hetero lung. Instability and overexpansion (atelectrauma and volutrauma) all due to hetero lung ventilation
Alveolar Overdistension into the Area of the Collapsed Alveoli

45. Courtesy from G. Niemann
What we think we see here is in vivo evidence supporting this hypothesis. There is a collapsed alveoli and the neighboring alveoli bulges into the void. All the other alveoli have neighbors which prevent them from overexpansion
Courtesy from G. Niemann

46. Homogeneous: Normal Lung
Large circle is lung and smaller circles alveoli. Notice no way for overexpansion at peak inspiration d/t interdependence b/w alveoli ie each prevents the others from overexpanding
The adjacent alveoli support each other to prevent overexpansion
This is example of homo lung
Minimal Change in Alveolar Size with Ventilation

47. Correlation of Inflection Points with Individual Alveolar R/D
DiRocco et al. Intensive Care Med

48. Courtesy from G. Niemann
What we think we see here is in vivo evidence supporting this hypothesis. There is a collapsed alveoli and the neighboring alveoli bulges into the void. All the other alveoli have neighbors which prevent them from overexpansion
Courtesy from G. Niemann

49. Best approach to recruitment: «Open the lung and keep it open»
Use the smallest Vt you can afford (you deal with a baby lung !)
then you have to work you through to find the optimal least PEEP approach = “Functional Approach to Recruitment”
Your tools at bedside: P/F ratio, PaCO2 and Cdyn

50. But there is a significant risk of overdistending many patients
There is no sound rational for fixed PEEP and FiO2
schemes as used in PEEP studies !
ARDS Network 6 versus 12 ml/kg: NEJM 2000;342:
ALVEOLI: NEJM 2004;351:
LOVES: Meade MO ;299(6):
But there is a significant risk of overdistending many patients