title: Optimization of positive end-expiratory pressure by volumetric capnography variables in lavage-induced acute lung injury.
abstract: BACKGROUND
  In the acute respiratory distress syndrome (ARDS), lung-protective ventilation strategies combine the delivery of small tidal volumes (VT) with sufficient positive end-expiratory pressure (PEEP). However, an optimal approach guiding the setting of PEEP has not been defined. Monitoring volumetric capnography is useful to detect changes in lung aeration.
  
  
  OBJECTIVE
  The aim of this study was to determine whether volumetric capnography may be a useful method to determine the optimal PEEP in ARDS.
  
  
  METHODS
  In 8 lung-lavaged piglets, PEEP was reduced from 20 to 4 cm H2O in steps of 4 cm H2O every 10 min followed by full lung recruitment. Volumetric capnography, respiratory mechanics, blood gas analysis, hemodynamic data and whole-lung computed tomography scans were obtained at each PEEP level.
  
  
  RESULTS
  After lung recruitment, end-expiratory lung volume progressively decreased from 1,160 ± 273 ml at PEEP 20 cm H2O to 314 ± 86 ml at PEEP 4 cm H2O. The ratio of alveolar dead space (VDalv) to alveolar VT (VTalv) and the phase III slope of volumetric capnography (SIII) reached a minimum at PEEP 16 cm H2O. At this PEEP level, overaerated lung regions were significantly reduced, nonaerated lung regions did not increase, and partial pressure of oxygen in arterial blood/fraction of inspired oxygen (P/F) and static respiratory system compliance (Crs) reached a maximum. At PEEP levels <16 cm H2O, nonaerated lung regions significantly increased, P/F and Crs deteriorated, and VDalv/VTalv and SIII began to increase.
  
  
  CONCLUSIONS
  In this surfactant-depleted model, PEEP at the lowest VDalv/VTalv and SIII allows an optimal balance between lung overinflation and collapse. Hence, volumetric capnography is a useful bedside approach to identify the optimal PEEP.
authors.affiliation: Department of Critical Care Medicine, Zhong-Da Hospital, Southeast University School of Medicine, Nanjing, PR China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.forename: Yingzi
authors.initials: Y
authors.lastname: Huang
authors.forename: Rui
authors.initials: R
authors.lastname: Tang
authors.forename: Qiuhua
authors.initials: Q
authors.lastname: Chen
authors.forename: Xia
authors.initials: X
authors.lastname: Hui
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.forename: Qing
authors.initials: Q
authors.lastname: Yu
authors.forename: Hongjie
authors.initials: H
authors.lastname: Zhao
authors.forename: Haibo
authors.initials: H
authors.lastname: Qiu
mesh_terms: D055371:Acute Lung Injury / Q000209:etiology / Q000628:therapy*; D000818:Animals; D001784:Blood Gas Analysis; D018893:Bronchoalveolar Lavage / Q000009:adverse effects*; D019296:Capnography / Q000379:methods*; D004195:Disease Models, Animal; D005260:Female; D008297:Male; D011175:Positive-Pressure Respiration / Q000379:methods*; D011659:Pulmonary Gas Exchange; D012121:Respiration, Artificial / Q000379:methods; D013552:Swine; D013990:Tidal Volume; D055397:Ventilator-Induced Lung Injury / Q000517:prevention & control*