Regional overdistension identified with electrical impedance tomography in the perflubron-treated lung

Regional lung overdistension occurring during high frequency oscillatory ventilation (HFOV) and partial liquid ventilation (PLV) was investigated in a prospective animal trial using 18 mechanically ventilated Yorkshire swine under general anesthesia. Lung injury was induced with saline lavage and augmented using large tidal volumes. Electrical impedance tomography (EIT) and regional lung histopathology were used to identify regional lung overdistension during HFOV. Lung injury was quantified using a histopathologic lung injury score. The animals were randomized to three groups (n = 6 animals in each group): a control group and two dose groups of perfluorooctyl bromide (PFOB) (PFOB-Lo 1.5 ml kg(-1) and PFOB-Hi 3 ml kg(-1)). The animals were transitioned from conventional ventilation to HFOV, and a slow inflation-deflation maneuver was performed by changing mean airway pressure (Paw) by 5 cmH(2)O every 15 min to a maximum Paw of 40 cmH(2)O. In dependent lung areas, the PFOB-Hi (3 ml kg(-1)) group, in comparison with the control group, was associated with significantly greater alveolar overdistension seen on lung histopathology (P < 0.001 compared to control), a decreased mean impedance (P < 0.05 compared to the control group) and a decreased ventilation-induced impedance change during HFOV (P < 0.05 compared to the control group). We conclude that treatment with PFOB-Hi during HFOV compared to a control group in an animal model of lung injury led to regional overdistension of dependent lung areas, as evidenced by increased alveolar overdistension on lung histopathology, decreased mean lung impedance and decreased HFOV-induced regional lung volume changes as measured by EIT.