Regional filling characteristics of the lungs in mechanically ventilated patients with acute lung injury

Objectives: The objective of the study was to determine regional pulmonary filling characteristics in 20 mechanically ventilated patients with acute lung injury. Methods: Regional filling characteristics were calculated from tracings of regional tidal volumes vs. global tidal volumes measured by electrical impedance tomography (EIT). These plots were fitted to a polynomial function of the second degree. Regional polynomial coefficients of the second degree characterized the curve linearity of the plots. Near-zero values of the polynomial coefficient indicated a homogeneous increase in regional tidal volumes during the whole inspiration. Positive values hinted at initial low regional tidal volume change suggesting lung volume recruitment. Negative values indicated late low regional tidal volume change implying hyperinflation of this lung region. Results: We found a broad heterogeneity of regional lung filling characteristics. The minimal regional polynomial coefficients varied from -2.80 to -0.56 (median -1.16), while the maximal regional polynomial coefficients varied from 0.58 to 3.65 (median 1.41). Conclusions: Measurements of regional filling characteristics by EIT may be a helpful tool to adjust the respiratory settings during mechanical ventilation to optimize lung recruitment and to avoid overdistension. It applies a non-pressure-related assessment to the mechanics of lung inflation and gives a view of the real problems underlying ventilatory strategies dependent on global characteristics.