Capnography reflects ventilation/perfusion distribution in a model of acute lung injury
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 (SIII) 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 cmH2O 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 cmH2O 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:
SIII showed the lowest value whenever lung recruitment and OL-PEEP were jointly applied and was associated with the lowest dispersion of ventilation and perfusion (DispR−E), the lowest ratio of alveolar dead space to alveolar tidal volume (VDalv/VTalv) and the lowest difference between arterial and end-tidal pCO2 (Pa−ETCO2). Spearman's rank correlations between SIII and DispR−E showed a =0.85 with 95% CI for (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.
Document Type: Research Article
Affiliations: 1: Department of Anesthesiology, Hospital Privado de Comunidad, Mar del Plata, Argentina 2: Department of Critical Care Medicine, Instituto de Investigación Sanitaria Fundación Jiménez Díaz., CIBERES, Madrid, Spain 3: CSEM Centre Suisse d'Electronique et de Microtechnique SA, Research Centre for Nanomedicine, Landquart, Switzerland 4: Laboratory – LIM09, Pulmonary Department, Hospital das Clínicas – Faculdade de Medicina, Universidade de São Paulo, São Paulo, Brazil 5: Department of Medical Sciences, Clinical Physiology, University Hospital, Uppsala, Sweden
Publication date: May 1, 2011