Fig. 2
Overdistention and collapse for two typical patients. a — A patient assigned to the PEEPhigher group. The top row displays ventilation distribution at four levels of PEEP (left to right: 28, 20, 16, and 10 cmH2O). Black indicates no ventilation, various shades of blue indicate ventilation, and white indicates the region where most ventilation is detected. At high PEEP levels, ventilation occurs in the dorsal lung regions, whereas the center of ventilation shifts ventrally at lower PEEP levels. The distribution of alveolar overdistention (orange) and alveolar collapse (white) is shown in the bottom row. At high PEEP levels, only a small amount of ventilation is detected in the ventral region as a result of overdistention. At low PEEP levels, ventilation shifts ventrally as a result of alveolar collapse. High PEEP resulted in a relatively small increase in alveolar overdistention and a large decrease in alveolar collapse. This patient was considered to have high recruitability and total PEEP was set at the lowest PEEP step above the intersection of both curves: 20 cmH2O., b — A patient assigned to the PEEPlower group. The top row displays ventilation distribution at four levels of PEEP (left to right: 24, 20, 12, and 6 cmH2O). A decrease in PEEP resulted in an increase in ventilation (light blue to white), and even at a low PEEP level of 6 cmH2O, ventilation in the dorsal lung regions is more or less preserved. At high PEEP levels, the relative amount of alveolar overdistention is 29%, which indicates severe alveolar overdistention. In contrast, at low PEEP levels, the amount of alveolar overdistention is significantly reduced, and only a small amount of alveolar collapse is identified (8%). This patient was considered to have low recruitability, and PEEP was set at 10 cmH2O., c — This plot represents the relative amount of alveolar overdistention and collapse as measured by EIT during a decremental PEEP trial. PEEP was set above at the lowest PEEP step above the intersection of the curves representing relative amount of alveolar overdistention and collapse (vertical lines). The patient in PEEPhigher group (orange triangles) had lower amounts of relative overdistention and higher amounts of alveolar collapse at the same PEEP level as compared to the patient assigned to a patient in PEEPlower group (blue dots)