ARDS - Tv < 6 mL/kg & Pplat < 28 is lung

protectiveJ.G. van der Hoeven

Radboudumc, Nijmegen

Myth

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

Low Tv in all?

ARDSnet. N Eng J Med 2000;342:1301-1308

Airway

Plung

Ppl

Transpulmonary pressure

Expiratory occlusion Inspiratory occlusion

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

Is 6 ml/kg always ideal?Certainly not

We should relate Tv to the remaining lung volume - compliance

Driving pressure

• Tidal volume/compliance

• ∆V : ∆V/∆P = ∆P

• During controlled mechanical ventilation ∆P is the difference between PEEP and plateau pressure

N = 3562

Amato MBP. N Engl J Med 2015;372:747-755Driving pressure D1

Amato MBP. N Engl J Med 2015;372:747-755

Bellani G. JAMA 2016;315:788-800

Hospital survival and driving pressure (observational)

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

Assisted ventilation may also induce VALI

• Unpredictable increase in transpulmonary pressure

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

Vt and transpulmonary pressure

Doorduin J. Anesthesiology 2015;123:181-190

Yoshida T. Am J Respir Crit Care Med 2013;188:1420-1427

…..Or induce Pendelluft phenomenon

Another risk factor

Transmural vascular pressure

Transmural vascular pressure

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