Reply to Frerichs et al.: Simple Electrical Impedance Tomography Measures for the Assessment of Ventilation Distribution.

From the Authors:

We thank Dr. Frerichs and colleagues for their interest in our research letter (1). We used both experimental data and clinical findings in our study to demonstrate that an excessive level of positive end-expiratory pressure (PEEP) could be easily—and almost immediately by visual inspection—identified by detecting a distribution of ventilation being predominantly dorsal as compared with a frequently predominantly ventral ventilation in patients ventilated at lower PEEP. We suggest that decreasing PEEP in such cases to obtain a more equilibrated dorsal-to-ventral distribution can be proposed to patients right away. We also showed from experimental data that using compliance of the respiratory system for this purpose would be misleading.

In our letter, we used the term “center of ventilation,” as proposed in a previous study (2). We appreciate Frerichs and colleagues’ comment regarding the fact that this does not correspond to the most recent definition of center of ventilation, as indicated in a recent consensus statement (3). We also acknowledge that using the center of ventilation, as proposed in that paper, requires a much more complex calculation than our own use of the distribution of ventilation. We believe that keeping this marker as simple as possible is important for clinical dissemination. We also believe that, based on the examples proposed, the center of ventilation as calculated from the reference value is much less clinically relevant for our purpose. We agree that a new denomination is needed for our index, and we propose the term “dorsal fraction of ventilation” as a better description.