title: 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.
abstract: BACKGROUND
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Hemodynamic Research Center, HemoLiege, University of Liege, Belgium. b.lambermont@chu.ulg.ac.be
authors.forename: Bernard
authors.initials: B
authors.lastname: Lambermont
authors.forename: Alexandre
authors.initials: A
authors.lastname: Ghuysen
authors.forename: Nathalie
authors.initials: N
authors.lastname: Janssen
authors.forename: Philippe
authors.initials: P
authors.lastname: Morimont
authors.forename: Gary
authors.initials: G
authors.lastname: Hartstein
authors.forename: Paul
authors.initials: P
authors.lastname: Gerard
authors.forename: Vincent
authors.initials: V
authors.lastname: D'Orio
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D005652:Functional Residual Capacity / Q000502:physiology*; D008170:Lung Compliance / Q000502:physiology; D011175:Positive-Pressure Respiration / Q000379:methods*; D012128:Respiratory Distress Syndrome / Q000503:physiopathology*; D012137:Respiratory System / Q000503:physiopathology*; D034421:Sus scrofa; D013552:Swine