To the Editor: We read with great interest the article about cutaneous mitochondrial Po2 (mito-Po2) by Römers et al. in the July 2016 issue of Anesthesiology. We congratulate them for their hard work in producing this demanding and important proof-of-concept study; it may prove to be revolutionary in transfusion medicine if a safe and feasible monitor of mito-Po2 becomes commercially available.

However, we would like to make the following points.
First, the authors administered intravenous anesthetics (ketamine, midazolam, sufentanil, and rocuronium) only and did not use inhalation agents at all. [...]
Second, in the shock state, the body will divert most of the cardiac output to the vital organs, including the brain and the heart, as the result of peripheral vasoconstriction. [...]
Third, as the authors elaborated in the article, measuring mito-Po2 at the skin may not reflect the oxygen tension (Po2) in the brain or the heart. [...]
Fourth, mixed venous oxygen saturation and Pao2 were obtained during the experiment but were not shown in table 1 or fig. 3. [...]
Finally, there is a cell-to-cell variability in mitochondrial number and function. Mitochondria play an important role in cell signaling, differentiation, and death. [...]