EIT to deliver mechanicalventilation

Claude Guérin MD PhDRéanimation MédicaleHôpital de la Croix RousseUniversité de LyonLyon, France

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CCCF October 2012

Disclosure

• Carefusion

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Outline

•Introduction

•Technique

•Applications

•Conclusions

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EIT: an attractive tool

• Non invasive

• Radiation free

• Available at bedside

• Monitoring

• Regional assessment of lung ventilation

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Introduction

EIT - Basic principles

• Electrode ring around thorax• Current injected by a pair of electrodes and potential difference measured

by all the others• Rapid rotation of repeated injection/measurement (13 Hz)• Change in tissue impedance from a baseline situation is measured • Air is weak electrical conductor • Image reconstruction by complex algorithms

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Low spatial resolution

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Matrix 32 x 32

pixels

High temporal resolution: Impedance-time curves

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Flow (L/min)

Right

Ventral

Dorsal

Left

Ventral

Dorsal

Overall

Impedance-time curves

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flow

ventral

dorsal

R L

1

2

3

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Validation of Lung Ventilation measurement

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Richard et al. CC 2009

EIT

PET

EIT

PET

Impedance-time curves

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VTeit

EELI

flow

S.I. 40 cm H2O x 40 sec

Functionnal image (fEIT)

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Functionnal image (fEIT)

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Local change

Overall change

Technical issues

Individual calibration attractive and feasible but not

standardized across subjects

Impedance-lung volume relationship depends on patient

morphology

Impedance depends on intracellularand extracellular liquid volume and

pulmonary blood volume

Sampled volume by EIT is limited and sois calibration by using global signal, i.e.

spirometer at the airway opening

Gas cranio-caudal redistribution duringcalibration induces error in local

calibration of impedance change in the plane of the electrode

Relative lung volumes

EIT measures change in impedance relative to reference

(DZ)

Absolute volume is not measured

If reference has changed between tested conditions, same lung volume change may promote

different EIT data

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Applications

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1. EELV measurement

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Bikker ICM 2009 Hinz ICM 2003

Biais 194 ml

Biais 0 ml

2. Regional lung inflation patterns

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16Hinz EJA 2006

global

regio

nal

VT EIT variation

3. Alveolar recruitment

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AUC

‘slope’: parameter ‘b’ in equation

y = axb + c

RVD: Time to reach a threshold value (10%

of maximum value)

Wrigge CCM 2008

ventral dorsal

CT-assessed recruitment

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Wrigge CCM 2008

r2 = 0.79 indirect ALI

r2 =0.15 direct ALI

AUC

slope

RVD

4. Intra-tidal recruitment

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19Dargaville

ICM 2010

16 piglets surfactant

depletion

PCV DP=10 cm H2O

VT amplitude and homogeneity

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Dargaville

ICM 2010

Right L

Lavaged Lung

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5. Estimation of overdistension and collapse

Costa ICM 2009

Pressure Controlled Ventilation

C=VTEIT/driving pressure at

pixel level

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Costa ICM 2009

5. Estimation of overdistension and collapse

6. Potential for recruitment

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Potential for recruitment

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Potential for recruitment

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Optimal PEEP

PEEP at potential of

recruitment ≤ 10%

Lowhagen 2010

Conclusions

• EIT now available at bedside

• Monitoring tool

• Should allow optimizing ventilator settings and interventions

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