‫“فإذا سويته ونفخت فيه من‬
‫روحي فقعوا له ساجدين“‬
‫ص ‪۷۲‬‬
Mechanical Ventilation
Strategies in ARDS
Nabil Abouchala, MD
Consultant
Pulmonary & Critical Care Medicine
abouhani@yahoo.com
Case presentation
• A 45-year-old man develops ARDS after sustaining
multiple broken bones in an automobile accident. The
man weighs 70 kg. Mechanical ventilation is initiated in
the AC mode with the following settings: (PEEP), 10 cm
H2O; (FiO2), 70%; respiration rate, 12/min.
• The most appropriate Tidal volume at this point:
–
–
–
–
–
(A)
(B)
(C)
(D)
(E)
1000 ml
420 ml
500 ml
560 ml
700 ml
Definitions
• The 1994 North American-European Consensus
Conference (NAECC) criteria:
– Onset - Acute and persistent
– Radiographic criteria - Bilateral pulmonary infiltrates
consistent with the presence of edema
– Oxygenation criteria - Impaired oxygenation
regardless of the PEEP concentration, with a
Pao2/Fio2 ratio  300 torr (40 kPa) for ALI and  200
torr (27 kPa) for ARDS
– Exclusion criteria - Clinical evidence of left atrial
hypertension or a pulmonary-artery catheter occlusion
pressure of  18 mm Hg.
Bernard GR et al., Am J Respir Crit Care Med 1994
Stratification System of Acute
Lung Injury GOCA
Letter
G
O
C
A
Meaning
Scale
Gas exchange
0
1
2
3
A
B
C
D
Pao2/Fio2  301
Pao2/Fio2 200 -300
Pao2/Fio2 101 – 200
Pao2/Fio2  100
Spontaneous breathing, no PEEP
Assisted breathing, PEEP 0-5 cmH2O
Assisted breathing, PEEP 6-10 cmH2O
Assisted breathing, PEEP  10 cmH2O
Organ failure
A
B
C
D
Lung only
Lung + 1 organ
Lung + 2 organs
Lung +  3 organs
Cause
1
2
3
Unknown
Direct lung injury
Indirect lung injury
0
1
No coexisting disease that will cause death within 5 yr
Coexisting disease that will cause death within 5 yr but not within 6
mo
Coexisting disease that will cause death within 6 mo
Gas exchange
(to be combined
with the numeric
descriptor)
Associated
diseases
2
Definition
Artigas A, et al. Am J Respir Crit Care Med. 1998.
The ARDS Lung
ARDS
Focal
Patchy
Diffuse
Chest x-ray
(zero PEEP)
Focal heterogeneous
loss of aeration in
caudal and dependent
lung region
Bilateral and diffuse xray densities
respecting lung apices
Bilateral and diffuse
hyperdensities
“White lungs”
Chest CT scan
(zero PEEP)
Loss of aeration
Upper lobes normally
aerated despite a
regional excess of lung
tissue – Lower lobes
poorly or non aerated
Lower lobes massively
nonaerated – The loss
of aeration involves
partially the upper lobes
Massive, diffuse and
bilateral non- or poorly
aerated lung regions –
No normally aerated
lung region
Response to PEEP
±
PEEP <10-12 cmH2O
Risk of overinflation of
the aerated lung regions
++++
Recruitment of non
aerated lung unit
Low potential for
recruitment
++++
Lung recruitment curve
Open lung concept
±
Rouby JJ, et al. Eur Respir J. 2003.
Rouby JJ, et al. Anesthesiology. 2004.
High potential for
recruitment
The ARDS Lung
Early phases of ARDS
Direct insult of the lung
Primary pulmonary ARDS
“Indirect” insult of the lung
Secondary extrapulmonary ARDS
Pathologic changes
Lung tissue consolidation
Severe intra-alveolar damage
(Edema, fibrin, collagen
neutrophil aggregates, red cells)
Microvascular congestion
Interstitial edema
Alveolar collapse
Less severe alveolar damage
End-expiratory lung volume
EELV


Static elastance of the total
respiratory system Est,rs


Static elastance of the chest
wall Est,w / Static lung
elastance Est,L
 / 
 / 
Intra-abdominal pressure


Response to PEEP
Est,rs  [Est,L >> Est,w]
Stretching phenomena
Est,rs  [Est,L  Est,w]
Recruitment of previously closed
alveolar spaces
Lung recruitment
±
++++
Gattinoni L, et al. Am J Respir Crit Care Med. 1998.
Stress distribution:
homogeneous system
FT
min
L. Gattinoni, 2003
max
Mead J et al. J. Appl. Physiol. 28(5):596-608 1970
Stress distribution:
high stiffness zone
min
L. Gattinoni, 2003
max
Mead J et al. J. Appl. Physiol. 28(5):596-608 1970
Ventilator-induced lung injury is initiated
by the application of excessive stress
Gattinoni, L. et al. CMAJ 2008;178:1174-1176
Copyright ©2008 Canadian Medical Association or its licensors
NEJM 2000;342:1334-1349
NEJM 2000;342:1334-1349
ARDS
Ventilator Strategy
Ventilator-induced Lung Injury
(VILI)
•
•
•
•
Barotrauma
Volutrauma
Atelectrauma
Biotrauma
Collapse
Over
Distension
Ventilation-Induced Lung Injury
(VILI)
Atelectrauma:
Repetitive alveolar collapse
and reopening of the underrecruited alveoli
Volutrauma:
Over-distension of normally
aerated alveoli due to
excessive volume delivery
Biotrauma:
Cytokines, complement,
prostanoids, leukotrienes,
O2- Proteases
*Dreyfuss: J Appl Physiol 1992
Respiratory Pressure/Volume (P/V) Curve
Healthy subject
In normal healthy volunteers, the P/V curve explore
the mechanical properties of the respiratory system
(lung + chest wall)
ARDS
RV, Residual volume; FRC, Functional residual capacity; TLC, Total lung capacity; UIP, Upper
inflection point; LIP, Lower inflection point. The critical opening pressure above which most of the
collapsed units open up and may be recruited - CLIN Compliance of the intermediate, linear segment
of the P/V curve
Maggiore SS, et al. Eur Respir J. 2003. Rouby JJ, et al. Eur Respir J. 2003.
Ventilator-induced Lung Injury
(VILI)
Upper
Deflection point
Lower
Inflection point
ARDS:
Pressure Volume Curves
Normal
Early ARDS
Volume
Late ARDS
Pressure
Pinsp = 40 mbar
PEEP = 5 mbar
Courtesy of Dr Neil
Macintyre
Muscedere JG et al. Am J Respir Crit Care Med 1994;149:1327-1334
The PEEP Effect
NEJM 2006;354:1839-1841
Barotrauma
Multiple Organ Failure!
ARDS: Baby lungs
Preventing Overdistention
and Collapse Injury
“Lung Protective” Ventilation
V
O
L
U
M
E
Add PEEP
Limit VT
Pressure
Limit Distending Pressure
Lung Protective Ventilator Protective VenLung
Protective Ventilator Strategies Strategies
volutrauma
zone of
overdistension
V
zone of derecruitment
and atelectasis
"safe"
window
UIP
DON’T EVEN
THINK
OF PARKING
HERE
LIP
atelectrauma
P
Courtesy of Dr Neil Macintyre
ARMA Trial
Intervention
TV (4-6 ml/Kg)
PEEP 8.5
Control
TV (10-12 ml/Kg)
PEEP 8.6
Balancing need for support vs
distending pressures/FiO2
Crs also better in the HIGH Vt group
Lung-Protective Ventilation
ARDS Network, 2000: Multicenter, randomized 861
patients
Tidal Volume (ml/kg)
Pplateau
PEEP
Actual PEEP
Result (p<0.001)
Lung-protective
ventilation
6
<30
Protocol
8.1
31.0%
Conventional
ventilation
12
<50
Protocol
9.1
39.8%
Principle for FiO2 and PEEP Adjustment
FiO2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
PEEP
5
5-8
8-10
10
10-14
14
14-18
18-24
NEJM 2000; 342: 1301-1308
Lung-Protective Ventilation
• Result:
– Lower 22% mortality (31% vs 39.8%)
– Increase ventilator-free days
NEJM 2000; 342: 1301-1308
Concerns when using lungprotective strategy…
•
•
•
•
•
•
•
Heterogeneous distribution
Hypercapnia
Auto-PEEP
Sedation and paralysis
Patient-ventilator dyssynchrony
Increased intrathoracic pressure
Maintenance of PEEP
What next?
Prone position
Inhaled nitric oxide
ECMO
High-frequency oscillation
Other Ventilator Strategies
• Lung recruitment maneuvers
• Prone positioning
• High-frequency oscillatory ventilation
(HFOV)
• ECMO
Lung Recruitment
• To open the collapsed
alveoli
• A sustained inflation
of the lungs to higher
airway pressure and
volumes
– Ex.: PCV, Pi = 45
cmH2O, PEEP = 5
cmH2O, RR = 10 /min,
I : E = 1:1, for 2
minutes
NEJM 2006; 354: 1775-1786
Lung Recruitment
NEJM 2006; 354: 1775-1786
Lung Recruitment
NEJM 2006; 354: 1775-1786
Lung Recruitment
• Potentially recruitable (PEEP 5  15 cmH2O)
– Increase in PaO2:FiO2
– Decrease in PaCO2
– Increase in compliance
Sensitivity : 71%
Specificity : 59%
• The effect of PEEP correlates with the
percentage of potentially recruitalbe lung
• The percentage of recruitable lung correlates
with the overall severity of lung injury
NEJM 2007; 354: 1775-1786
Lung Recruitment
• The percentage of potentially recruitable
lung:
– Extremely variable,
– Strongly associated with the response to
PEEP
• Not routinely recommended
Prone Position
Prone Position
• Mechanisms to
improve oxygenation:
– Increase in endexpiratory lung volume
– Better ventilationperfusion matching
– More efficient drainage
of secretions
Prone Position
 Improved gas exchange
 More uniform alveolar
ventilation
 Recruitment of atelectasis
in dorsal regions
 Improved postural
drainage
 Redistribution of perfusion
away from edematous,
dependent regions
Prone Positioning
Prone Position
NEJM 2001;345:568-573
Prone Position
NEJM 2001;345:568-573
Prone Position
• Improve oxygenation in about 2/3 of all
treated patients
• No improvement on survival, time on
ventilation, or time in ICU
• Might be useful to treat refractory
hypoxemia
• Optimum timing or duration ?
• Routine use is not recommended
High-Frequency Oscillatory
Ventilation (HFOV)
HFV - the “ultimate” lung
protective strategy?
Over-distended
Protected
Under-recruit
HFOV
Frequency: 180-600 breaths/min (3-10Hz)
Effect of HFOV on gas exchange in
ARDS patients
AJRCCM 2002; 166:801-8
Survival difference of ARDS patients
treated with HFOV or CMV
30-day: P=0.057
90-day: P=0.078
AJRCCM 2002; 166:801-8
HFOV
• Complications:
– Recognition of a
pneumothorax
– Desiccation of secretions
– Sedation and paralysis
– Lack of expiratory filter
• Failed to show a mortality
benefit
• Combination with other
interventions ?
Chest 2007; 131:1907-1916
Acute Lung injury
• Decreased lung compliance results in high
airway pressures
• Low tidal volume 6-8 ml/kg ideal body weight
• Maintain IPP  30 cm H2O
• PEEP to improve oxygenation
Conclusions
• The only treatment that shows mortality
benefit:
– lung-protective ventilation strategy
– Low tidal volume (6ml/Kg), high PEEP,
adequate Pplat (<30 cmH2O)
• Modalities to improve oxygenation:
– Prone position, steroid, fluid treatment, steroid,
HFOV, NO
• Combining other treatments:
– Activated protein C, antibiotics, EGDT…etc