Identification of regional overdistension, recruitment and cyclic alveolar collapse with electrical impedance tomography in an experimental ARDS modelReport as inadecuate




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Critical Care

, 20:119

First Online: 03 May 2016Received: 21 September 2015Accepted: 19 April 2016

Abstract

BackgroundInformation on regional ventilation distribution in mechanically ventilated patients is important to develop lung protective ventilation strategies. In the present prospective animal study, we introduce an electrical impedance tomography EIT-based method to classify lungs into normally ventilated, overinflated, tidally recruited-derecruited and recruited regions.

MethodsAcute respiratory distress syndrome ARDS was introduced with repeated bronchoalveolar lavage in ten healthy male pigs until the ratio of arterial partial pressure of oxygen and fraction of inspired oxygen PaO2-FiO2 decreased to less than 100 mmHg and remained stable for 30 minutes. Stepwise positive end-expiratory pressure PEEP increments were performed from 0 cmH2O to 30 cmH2O with 3 cmH2O increase every 5 minutes. Respiratory system compliance Crs, blood gases and hemodynamics were measured at the same time. Lung regions at end-expiration and during tidal breathing were identified in EIT images.

ResultsOverinflated regions contain air at end-expiration but they are not or are only minimally ventilated. Recruited regions compared to reference PEEP level contain air at end-expiration of arbitrary PEEP level but not at that of reference PEEP level. Tidally recruited-derecruited regions are not represented in lung regions at end-expiration but are ventilated during tidal breathing. The results coincided with measurements of blood gases. The coefficient for correlation between the number of recruited pixels and PaO2-FiO2 was 0.89 ± 0.12 p = 0.02.

ConclusionThe proposed novel EIT-based method provides information on overinflation, recruitment and cyclic alveolar collapse at the bedside, which may improve the ventilation strategies used.

KeywordsMechanical ventilation Acute respiratory distress syndrome Electrical impedance tomography Recruitment-derecruitment Overinflated AbbreviationsARDSacute respiratory distress syndrome

Crsrespiratory system compliance

CTcomputed tomography

CVPcentral venous pressure

EITelectrical impedance tomography

FiO2fraction of inspired oxygen

GIglobal inhomogeneity

HUHounsfield units

MAPmean arterial pressure

PaCO2partial pressure of CO2 in arterial blood

PaO2partial pressure of O2 in arterial blood, PAWP, pulmonary arterial wedge pressure

PEEPpositive end-expiratory pressure

Pplatplateau pressure

RVDregional ventilation delay index

VTtidal volume

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