Here, it will be handled how oxygenaton of a tissue volume can be evaluated.
It is not easy to evaluate if an organ gets enough oxygen (O2) – often, not or hardly possible. The mostly used tools to judge oxygenation status are two methods: measuring exhaled values from the lung; and evaluating (infrared) light signals, either reflected from the skin or shining through. Both have pro's and cons, but always are indirect.
Lung values are indirect so do not reflect what is happening in the individual organs, but are valuable as a monitoring tool. In particular, when also body oxygen consumption (˙VO2) is measured, in a (semi-)closed system. Under a limit value is a severe warning. It can be done by monitoring PO2 and air flow in the expired air simultaneously:
(Infra)red light meaurements actually measure hemoglobin, and there is a lot of technical and theoretical stuff involved to eventually calculate the result. There is not always a direct relation between hemoglobin and tissue O2. And tissue can be highly heterogeneous, underestimating regions lacking O2.
Some of this can be found in ..........