The oxygen trail: measurement

Tissue hypoxia may be defined as abnormal oxygen utilization such that cell s are experiencing anaerobic metabolism. Tissue hypoxia can be defined bioc hemically by low levels of ATP, high levels of NADH, or decreased oxidised cytochrome aa,. It is possible to measure these biochemical markers in the laboratory setting with, for example, nuclear magnetic resonance spectrosco py. However, this is not as yet a clinical option. There is no 'gold standa rd' for the diagnosis of clinical hypoxia. We can detect the gross conseque nces of tissue hypoxia, such as organ dysfunction and metabolic markers of anaerobic metabolism (e.g. lactic acidosis). We have also become familiar w ith the measurement of both global and regional oxygen dispatch and consump tion. However, organ dysfunction and metabolic acidosis consistent with est ablished tissue hypoxia commonly exists in the presence of normal and even supra normal global measures of oxygen dispatch and consumption. Therefore, we should ideally make measurements at the end of the oxygen trail, i.e. c ellular oxygen delivery and effective utilization.