..According to the intra-tidal compliance-volume curves calculated with the SLICE method, another optimal PEEP level with respect to lung mechanics was obtained for every patient. Figure Figure44 shows typical intra-tidal compliance-volume curves in the CYC202 same patient as in Figures Figures22 and and3.3. Positive slope (upwards direction) of the compliance-volume curves at a low PEEP indicates ongoing recruitment in inflation, while a negative slope (downwards direction) indicates overdistension of alveoli. PEEP is optimized when quasi-constant compliance within tidal breath is obtained [12].Figure 4The shape of intra-tidal dynamic compliance calculated with the SLICE method in the same patient as in Figures 1 and 2. An upward slope indicates recruitment, a downward slope indicates overdistension and a quasi-horizontal shape indicates that neither .

..Figure Figure55 shows the comparison of these methods in a box plot and Bland-Altman plots (GI index vs. dynamic compliance; GI index vs. compliance-volume curve). No significant differences in the results were found between the GI index method (12.2 �� 4.6 mbar) and the dynamic compliance method (11.4 �� 2.3 mbar, P > 0.6), or between the GI index and the compliance-volume method (12.2 �� 4.9 mbar, P > 0.6). Considering the quasi-plateau phases in compliance-pressure curves, the large differences between the results obtained with the GI index and the dynamic compliance method in some patients were explainable. No bias of results was observed in the Bland-Altman analysis.

Figure 5Comparison of the optimal PEEP determined with the GI index, dynamic compliance and compliance-volume curve method. Left = box plot. The boxes mark the quartiles while the whiskers extend from the box out to the most extreme data value within 1.5 times …DiscussionIn this study, we investigated the feasibility of our approach to optimize PEEP with respect to the homogeneity of pulmonary ventilation distribution using the GI index. In a previous study [10], we have demonstrated that the EIT-based GI index quantified the tidal volume distribution within the lung and showed good reliability and inter-patient comparability. Alveolar recruitment with less overdistension of the lung tissue would actually lead to a more homogeneous pulmonary air distribution. The feasibility of the GI index as a new tool in PEEP optimization was confirmed by the present retrospective study.

The results were comparable with the global dynamic compliance method [11] and the intra-tidal compliance-volume curves produced by the SLICE method [12].Although differences of air distribution in the lung can be observed in EIT images on a qualitative level (Figure (Figure1),1), Cilengitide it is difficult to identify a superior PEEP level with respect to homogeneity of ventilation distribution.