Regional pulmonary pressure volume curves in mechanically ventilated patients with acute respiratory failure measured by electrical impedance tomography

Background: We hypothized, that in mechanically ventilated patients with acute respiratory failure, regional pressure volume curves differ markedly from conventional global pressure volume curves of the whole lung. Methods: In nine mechanically ventilated patients with acute respiratory failure during an inspiratory low-flow manoeuvre, conventional global pressure volume curves were registered by spirometry and regional pressure volume curves in up to 912 regions were assessed simultaneously using electrical impedance tomography. We compared the lower (LIP) and upper (UIP) inflection points obtained from the conventional global pressure volume curve and regional pressure volume curves. Results: We identified from the conventional global pressure volume curves LIP [3-11 (8) cmH(2)O] in eight patients and UIP [31-39 (33) cmH(2)O] in three patients. Using electrical impedance tomography (EIT), LIP [3-18 (8) cmH(2)O] in 54-264 (180) regions and UIP [23-42 (36) cmH(2)O] in 149-324 (193) regions (range and median) were identified. Lung mechanics measured by conventional global pressure volume curves are similar to the median of regional pressure volume curves obtained by EIT within the tomographic plane. However, single regional pressure volume curves differ markedly with a broad heterogeneity of lower and upper inflection points. Conclusion: Lower and upper inflection points obtained from conventional global pressure volume curves are not representative of all regions of the lungs.