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Open Access Highly Accessed Research

Comparison of functional residual capacity and static compliance of the respiratory system during a positive end-expiratory pressure (PEEP) ramp procedure in an experimental model of acute respiratory distress syndrome

Bernard Lambermont12*, Alexandre Ghuysen13, Nathalie Janssen13, Philippe Morimont12, Gary Hartstein3, Paul Gerard14 and Vincent D'Orio13

Author Affiliations

1 Hemodynamic Research Center, HemoLiege, University of Liege, Belgium

2 Medical Intensive Care Unit, Department of Medicine, University Hospital of Liege, Belgium

3 Emergency Care Department, University Hospital of Liege, Belgium

4 Department of Statistics, University of Liege, Belgium

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Critical Care 2008, 12:R91  doi:10.1186/cc6961

Published: 16 July 2008

Abstract

Introduction

Functional residual capacity (FRC) measurement is now available on new ventilators as an automated procedure. We compared FRC, static thoracopulmonary compliance (Crs) and PaO2 evolution in an experimental model of acute respiratory distress syndrome (ARDS) during a reversed, sequential ramp procedure of positive end-expiratory pressure (PEEP) changes to investigate the potential interest of combined FRC and Crs measurement in such a pathologic state.

Methods

ARDS was induced by oleic acid injection in six anesthetised pigs. FRC and Crs were measured, and arterial blood samples were taken after induction of ARDS during a sequential ramp change of PEEP from 20 cm H2O to 0 cm H2O by steps of 5 cm H2O.

Results

ARDS was responsible for significant decreases in FRC, Crs and PaO2 values. During ARDS, 20 cm H2O of PEEP was associated with FRC values that increased from 6.2 ± 1.3 to 19.7 ± 2.9 ml/kg and a significant improvement in PaO2. The maximal value of Crs was reached at a PEEP of 15 cm H2O, and the maximal value of FRC at a PEEP of 20 cm H2O. From a PEEP value of 15 to 0 cm H2O, FRC and Crs decreased progressively.

Conclusion

Our results indicate that combined FRC and Crs measurements may help to identify the optimal level of PEEP. Indeed, by taking into account the value of both parameters during a sequential ramp change of PEEP from 20 cm H2O to 0 cm H2O by steps of 5 cm H2O, the end of overdistension may be identified by an increase in Crs and the start of derecruitment by an abrupt decrease in FRC.