Lung Stress and Strain in

ARDS

2016, Toronto

Luciano Gattinoni, MD, FRCP

Georg-August-Universität Göttingen

Germany

Chest wall elastance

EtotEtot

cmH2O

StiffStiff

2525

LEEL

“Soft”“Soft”

EwEw

55

StiffStiff

1515

EwEw

“Soft”“Soft”

1515

LEEL

EtottotE

Clinical equivalents

Stress PL transpulmonary pressure

Strain VT / FRC

The linkage is the specific elastance

PL VT

FRC= *

Elspec

Barotrauma Volotrauma

FRCml

TLCml

Sp Ecm H2O

PL (TLC)

cm H2O

2.5 7.5 4 8

300 900 6 12

2000 6000 12 24

VT/kg (mL/kg)

6 8 10 12

Str

ain

0.20.40.60.81.01.21.41.61.82.02.22.42.62.83.0

ALI patients

ARDS patients

B

Chiumello et al. Am J Respir Crit Care Med. 2008 Aug 15;178(4):346-55.

PEEP 5 cmH2O

50 sbj

Strain vs VT/kg IBW

Airway plateau pressure (cmH2O)

0 10 20 30 40 50 60

0

10

20

30

40

50

60

Airway plateau pressure (cmH2O)

0 10 20 30 40 50 60

T

ran

spulm

on

ary

pla

teau

pre

ssue

(cm

H2O

)

0

10

20

30

40

50

60

A

Surgical control group

Medical control group ARDS patients

ALI patients

B

Chiumello et al, Am J Respir Crit Care Med. 2008

Slope PL/Paw = Ew/Etot [0.2 - 0.8]

Strain (dVgas/Vgas0)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Str

ess

(PL

, cm

H2

O)

0

5

10

15

20

25

30

35

40

45

50

55

Stress-strain curve of healthy pigs

Specific Lung

Elastance

5.8 cmH2O

Protti A. et al. Am J Respir Crit Care Med. 2011 Feb 4.

TLC

FRC

Lun

g V

olu

me

VT 100%

VPEEP 0%

VT 75%

VPEEP 25%

VT 50%

VPEEP 50%

VT 25%

VPEEP 75%

Protti et al. Crit Care Med. 2013 Feb 4.

Tidal Strain

P*ΔV = Energy Input

Dissipated Undissipated

Surface Tension

Sliding EM

Opening and ClosingElastic System

PEEP *ΔV = Energy Input = 0

Continuous Strain

Pressure

0 10 20 30 40 50 60

Volu

me

0

200

400

600

800

1000

1200

PE

EP

Pea

k

Pre

ssure

PEEP Volume

Total Inspiratory Volume

Pressure

0 10 20 30

Volu

me

0

200

400

600Z

EE

P

Pea

k

Pre

ssure

Total Inspiratory Volume

Pressure

0 10 20 30 40

Volu

me

0

200

400

600

800

1000

1200

PE

EP

Pea

k

Pre

ssure

PEEP Volume

Total Inspiratory Volume

EXAPLES OF ENERGY

COMPUTATIONS AT

DIFFERENT PRESSURES

ZEEP

LOW PEEP HIGH PEEP

Global stress able to damage healthy (or “baby”?) lung

in clinical practice is uncommon

However, when the lung starts to deteriorate the rate of

damage is impressively fast, why?

If global stress is so rare, how can we explain the

following slide?

ARR = absolute

risk reduction

Hager et al. Am J Respir Crit Care Med. 2005 Nov 15;172(10):1241-5.

min max

Stress distribution:

high stiffness zone

Mead J et al. J. Appl. Physiol. 28(5):596-608 1970

Healthy subject

Moderate ARDS

Severe ARDS

Average ratio in normal subjects : 1.37±0.15

Hypothesis

Lesions should first occur where

physiological stress risers are located

Before appearance first new densities

TIME 1: 5.7±6.5 hours

END EXPIRATION END INSPIRATION

Courtesy of dr. Cressoni M.

First CT scan with new densities

TIME 2: 8.4±6.3 hours

END EXPIRATION END INSPIRATION

Courtesy of dr. Cressoni M.

Last CT scan with distinguishable densities

TIME 3: 15±12 hours

END EXPIRATION END INSPIRATION

Courtesy of dr. Cressoni M.

First CT scan with one-field edema

TIME 4: 18±11 hours

END EXPIRATION END INSPIRATION

Courtesy of dr. Cressoni M.

First CT scan with all-field edema

TIME 5: 20±11 hours

END EXPIRATION END INSPIRATION

Courtesy of dr. Cressoni M.

Hours0 5 10 15 20 25

Sev

erit

y t

rend

CT scan only

+ Lung mechanics

+ Gas Exchange

T2

T3

T4-5

VILI cumulative time course

Courtesy of dr. Cressoni M.

PET

FDG UPTAKE

CT SCAN

INFLATION INHOMOGENEITY

LUNG IMAGING

Ki/lung inhomogeneity interaction and gas/tissue

composition

MILD

MODERATE

SEVERE

Lung protective strategy

Less energy

+

More homogeneous lung