We read with interest the recent article by Zarantonello et al.1  on the physiologic effects of prone positioning on ventilation and perfusion distribution, oxygenation, and lung mechanics in COVID-19 acute respiratory distress syndrome patients. We would like to first congratulate the authors for the nicely conducted study that once again proved the clinical applicability of electrical impedance tomography for the assessment of ventilation–perfusion matching at the bedside. We acknowledge the clinical significance of the findings, but we wish to point out that several parts of the electrical impedance tomography methodology were incorrectly described in the article.

In the Methods section, the authors described how the lung areas that were (1) perfused but not ventilated, (2) ventilated but not perfused, and (3) both ventilated and perfused were “divided by the sum of ventilated and perfused pixels” to calculate the corresponding relative fractions of the lung area in percentages, i.e....

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