Capnography reflects ventilation/perfusion distribution in a model of acute lung injury

Acta Anaesthesiol Scand. 2011 May;55(5):597-606. doi: 10.1111/j.1399-6576.2011.02404.x. Epub 2011 Feb 22.


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.

Conclusion: 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acute Lung Injury / physiopathology*
  • Animals
  • Blood Gas Analysis
  • Capnography / statistics & numerical data*
  • Carbon Dioxide / blood
  • Carbon Dioxide / metabolism
  • Data Interpretation, Statistical
  • Hemodynamics / physiology
  • Oxygen / blood
  • Oxygen Consumption / physiology
  • Positive-Pressure Respiration
  • Respiratory Mechanics / physiology
  • Swine
  • Ventilation-Perfusion Ratio / physiology*
  • Vital Capacity / physiology


  • Carbon Dioxide
  • Oxygen