title: Capnography reflects ventilation/perfusion distribution in a model of acute lung injury.
abstract: BACKGROUND
  Changes in the shape of the capnogram may reflect changes in lung physiology. We studied the effect of different ventilation/perfusion ratios (V/Q) induced by positive end-expiratory pressures (PEEP) and lung recruitment on phase III slope (S(III)) of volumetric capnograms.
  
  
  METHODS
  Seven lung-lavaged pigs received volume control ventilation at tidal volumes of 6 ml/kg. After a lung recruitment maneuver, open-lung PEEP (OL-PEEP) was defined at 2 cmH(2)O above the PEEP at the onset of lung collapse as identified by the maximum respiratory compliance during a decremental PEEP trial. Thereafter, six distinct PEEP levels either at OL-PEEP, 4 cmH(2)O above or below this level were applied in a random order, either with or without a prior lung recruitment maneuver. Ventilation-perfusion distribution (using multiple inert gas elimination technique), hemodynamics, blood gases and volumetric capnography data were recorded at the end of each condition (minute 40).
  
  
  RESULTS
  S (III) showed the lowest value whenever lung recruitment and OL-PEEP were jointly applied and was associated with the lowest dispersion of ventilation and perfusion (Disp(R-E)), the lowest ratio of alveolar dead space to alveolar tidal volume (VD(alv)/VT(alv)) and the lowest difference between arterial and end-tidal pCO(2) (Pa-ETCO(2)). Spearman's rank correlations between S(III) and Disp(R-E) showed a ρ=0.85 with 95% CI for ρ (Fisher's Z-transformation) of 0.74-0.91, P<0.0001.
  
  
  CONCLUSIONS
  In this experimental model of lung injury, changes in the phase III slope of the capnograms were directly correlated with the degree of ventilation/perfusion dispersion.
authors.affiliation: Department of Anesthesiology, Hospital Privado de Comunidad, Mar del Plata, Argentina. gtusman@hotmail.com
authors.forename: G
authors.initials: G
authors.lastname: Tusman
authors.forename: F
authors.initials: F
authors.lastname: Suarez-Sipmann
authors.forename: S H
authors.initials: SH
authors.lastname: Bohm
authors.forename: J B
authors.initials: JB
authors.lastname: Borges
authors.forename: G
authors.initials: G
authors.lastname: Hedenstierna
mesh_terms: D055371:Acute Lung Injury / Q000503:physiopathology*; D000818:Animals; D001784:Blood Gas Analysis; D019296:Capnography / Q000706:statistics & numerical data*; D002245:Carbon Dioxide / Q000097:blood / Q000378:metabolism; D003627:Data Interpretation, Statistical; D006439:Hemodynamics / Q000502:physiology; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology; D011175:Positive-Pressure Respiration; D015656:Respiratory Mechanics / Q000502:physiology; D013552:Swine; D014692:Ventilation-Perfusion Ratio / Q000502:physiology*; D014797:Vital Capacity / Q000502:physiology
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen