Measuring end-expiratory lung volume

Giacomo Bellani, M.D., Ph.D.University of Milano-Bicocca

Monza, Italygiacomo.bellani1@unimib.it

Conflicts of interest

Personal:• Lecturing fees from GE

Institutional, research grants from:• Draeger• Maquet• Chiesi Farmaceutici

Which «lung volume» ?

Functional Residual Capacity (FRC)Functional Residual Capacity (FRC)Volume of gas in the lung at the end of a physiologic Volume of gas in the lung at the end of a physiologic

expiration expiration Relaxation volume of respiratory systemRelaxation volume of respiratory system

End Expiratory Lung Volume (EELV)End Expiratory Lung Volume (EELV)Volume of gas in the lung at end expiration during Volume of gas in the lung at end expiration during mechanical ventilation with PEEPmechanical ventilation with PEEP

EELV @ 0 cmH2O= FRC

• How do we measure End-expiratory lung volume?

• Why should we measure end-expiratory lung volume?

TechniquesCT scan

• Precise quantitative assessment• Radiological exposure+patient transfer

Closed circuit• Need for a dedicated tracer+closed system• No need for «fast» response concentration

measurements - offline measurementOpen circuit muti-breath washin/washout

• Potentially no need for a gas tracer• Fast response measurement, synchrony with tidal

ventilation

TechniquesCT scan

• Precise quantitative assessment• Radiological exposure+patient transfer

Closed circuit• Need for a dedicated tracer+closed system• No need for «fast» response concentration

measurements - offline measurementOpen circuit muti-breath washin/washout

• Potentially no need for a gas tracer• Fast response measurement, synchrony with tidal

ventilation

Closed Dilution Technique

VVff = V = Vii + EELV + EELV

Mass conservation

CiCiViVi

FRC ?FRC ?

CfCfVfVf

ViViCfCfCiCi

ViViEELVEELV -=

VVii* C* Cii = V = Vff* C* Cff

TechniquesCT scan

• Precise quantitative assessment• Radiological exposure+patient transfer

Closed circuit• Need for a dedicated tracer+closed system• No need for «fast» response concentration

measurements - offline measurementOpen circuit muti-breath washin/washout

• Potentially no need for a gas tracer• Fast response measurement, synchrony with tidal

ventilation

70 %

30 %O2

N2

50 %

50 %

FiN2=70%

Vt

FeN2

600 ml

1400 ml

1000 ml

1000 ml ml.

ml

..

Nml2000

20

400

5070

400 2

Multibreath nitrogen washout

Wrigge H et al Intensive Care Med 1998; 24: 487

Off-line correction of viscosity effect on sidestream delay time and pneumothacografic measurments

Derives N2 concentration from: 100%- [CO2]- [CO2]

Uses end-tidal concentration (no need for synchronization)

What about Pressure Support ?

0

1000

2000

3000

4000

0 1000 2000 3000 4000

EELV by He dilution (ml)

EE

LV

by

GE

En

gst

rom

(m

l)Volume Control

R2 = 0.8353

Pressure Support

Using a 20% variation in FiO2:

Bellani G, unpublished

FRC INview (Engstrom carestation)

• How do we measure End-expiratory lung volume?

• Why should we measure end-expiratory lung volume?

EELV is profoundly reduced in ARDS• Estimate of alveolar

recruitment• Determinant of VILI

Why should we measure end-expiratory lung volume?

EELV is profoundly reduced in ARDS

• Estimate of alveolar recruitment

• Determinant of VILI

Why should we measure end-expiratory lung volume?

Alveolar recruitment by P-V curve

Maggiore S. et al, Am J Resp Crit Care Med, 2001

Effect of recruitment on FRC (0 cmH2O)

Patroniti N et al., CCM 2010

A simplified approachAssessing alveolar recruitment by EELV

PEEP = 0

Compliance=30 ml/cmH2OEELV= 1000 ml

PEEP=10

Expected EELV increase: 30 * 10= 300 ml

No recruitmentEELV= 1300 ml

RecruitmentEELV = 1600 ml

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

4 14

PEEP (cmH2O)

EE

LV

(l)

0

5

10

15

20

25

30

35

Crs

(m

l/cm

H2O

)

6 8 10 12

1350 ml

Crs 29 expected EELV increase 174 ml

1524 l

1950 l

true EELV increase 600 ml

∆EELV / PEEP change = 600 / 6 = 100 ml/cmH2O

EELV is profoundly reduced in ARDS• Estimate of alveolar

recruitment• Determinant of VILI

Why should we measure end-expiratory lung volume?

EELV

VE (L/min)

RATIO

NORMAL

ARDS

2500 < 7 < 2.8

1000 > 15 > 15

SPECIFIC HYPERVENTILATION

Vt/F

RC

End-expiration End-inspiration PETEELVnormally-aerated

Vtnormally-aerated

Kinormally-aerated

High activity

Low activity

- 1000

100

-500

Regional distension and inflammation

Bellani G et al., Am J Resp Crit Care Med, 2011

The role of tidal volume/EELV

Bellani G et al., Am J Resp Crit Care Med, 2011

Conclusions:o Measurement of end-expiratory lung volume is

now available:RESEARCH TOOL → CLINICAL TOOL

o Useful in estimating lung recruitmentoCan it help in setting PEEP? Yeso Is it being used to set PEEP? Don’t know

o Possible role in adjusting tidal volume?