ards - tv < 6 ml/kg & pplat < 28 is lung protective beademing... · ards - tv < 6...
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The evolution of Ventilation Induced Lung Injury
Low tidal volume Stress and strain Driving pressure Power
Controlled ventilation Assisted ventilation Spontaneous ventilation
2000 2017
Animal experiments showed us the right direction!
Extra
vasc
ular
lung
wat
er (m
l/kg)
0
2
4
6
8
10
Control MV HV / HP HV / HP / PEEP HV / LP LV / HP
Dreyfuss D. Am Rev Respir Dis 1988;137:1159-1164
Another classical experiment
Tracheal intubation (N=31), spontaneous breathing, FiO2 21%
Sodium salicylate in cisterna magna Sodium salicylate in cisterna magna
MV - sedationand paralysis
Spontaneoushyperventilation
4.5 - 13.5 hours
Saline 0.9% in cisterna magna
Spontaneousventilation
16 10 5
Room air (10) 3% CO2 (6) Room air (5) 3% CO2 (5) Room air (5)
A B C
Mascheroni D. Intensive Care Med 1988;15:8-14
Outcome measuresA B C
Animals (N) 16 10 5
Experimental duration (h) 32.3 ± 3 37 37
Hyperventilation (h) 8.4 ± 3 - -
Salicylate infections (N) 6.2 ± 2 9 -
VE (ml/kg/min) 578 ± 200 168 ± 22 147 ± 23
PaO2 (mmHg) 60 ± 16 83 ± 12 84 ± 8
A-a difference (mmHg) 431 ± 139 227 ± 39 244 ± 42
Crs (mL/cmH2O) 25.3 ± 7 34.6 ± 10 34 ± 6
Lung/body weight 19.5 ± 7 14.5 ± 2 13.7 ± 2
Surface tension (dyn/cm) 12.8 ± 6 11.5 ± 6 13.7 ± 2
Normal lungs (autopsy) 2/16 10/10 5/5
Dead (N) 5 0 0
Mascheroni D. Intensive Care Med 1988;15:8-14
The ARDSnet trial%
0
20
40
60
80
Mortality Free of MV D28 Barotrauma
11
55
39,8
10
65,7
31
N = 861
***
***
Tv (m
l/kg
IBW
)
0
5
10
15
Low Tv High Tv
Ppla
t (cm
H2O
)
0
10
20
30
40
50
D1 D3 D7
ARDSNET. New Engl J Med 2000;342:1301-1308
Ventilator strategy based on TP pressure
Com
plia
nce
(ml/c
m H
2O)
0
15
30
45
60
Baseline 72 hours
Control EsophagealP = 0.005
Ratio
dea
d sp
ace:
tidal
ve
ntila
tion
0
0,2
0,4
0,6
0,8
Baseline 72 hours
P = NS
After adjustment for baseline APII score the esophageal group had a lower mortality (RR 0.46, 95% CI 0.19 - 1.0, p = 0.049)
Talmor D. N Engl J Med 2008;359:2095-2104
Lung stress and strain
Lung stress =
Force that distends the lung
= Transpulmonary
pressure
Maximal inspiratory capacity
Static (PEEP)
Dynamic (Tv)
L U N G
d e f o r m a t i o n
Strain
Static strain
Dynamic strain
VILI
Local stressraisers
Driving pressure
• Tidal volume/compliance
• ∆V : ∆V/∆P = ∆P
• During controlled mechanical ventilation ∆P is the difference between PEEP and plateau pressure
Driving pressureSecondary analysis Acurasys and Proseva trial D1 (N = 787)
Tv (S) 6.2 ± 0.8 versus (NS) 6.3 ± 0.8 mL/kg IBW
Guérin C. Crit Care 2016;20:384
Adju
sted
pro
babi
lity
of d
eath
(d 9
0)
0
0,1
0,2
0,3
0,4
0,5
Driving pressure (D1), cm H2O8 (5-9) 10 (10-11) 13 (12-13) 15 (14-16) 19 (17-31)
***P = 0.021
Transpulmonary pressure during CMV and PSV∆
Plun
g (c
mH
2O)
0
6
12
18
24
CMV High PSV Medium PSV Low PSV
Maximum Mean
Bellani G. Crit Care 2016;20:142
In conclusion• Individual mechanical breath parameters (Tv and Pplat)
are not directly correlated with VILI
• The size of the lung that is being ventilated and local stress raisers (inhomogeneity) are the most important determinants of VILI
• Driving pressure is a practical way to correlate Tv with the size of the remaining lung
• Assisted (spontaneous) ventilation in the early phase of ARDS had several hidden dangers