Hypoxanthine, a purine derivative, is a potential free radical generator and could be used as an indicator of hypoxia.

Hypoxanthine is a potential free radical generator. Hypoxanthine seems to play a role in posthypoxic reoxygenation cell injury through oxygen radical production and is therefore involved in the pathogenesis of a number of diseases. Hypoxanthine also modulates a number of other processes because it reacts with benzodiazepine receptors and inhibits phosphodiesterase in the brain. Hypoxanthine inhibits the effect of several cytotoxic drugs and may therefore influence treatment with such drugs[1].

In pigs, a linear increase of plasma hypoxanthine with duration of hypoxemia is found, and there is no difference between arterial and venous plasma. There are good correlations between hypoxanthine and lactate, base deficit and pH. There is also a direct relationship between survival time and increase in plasma hypoxanthine. Survival time correlates negatively with the rate of hypoxanthine increase (r=-0.62).All animals die when hypoxanthine exceeds 125 pM/liter. The increase of hypoxanthine therefore reflected the prognosis of acute hypoxia in contrast to base deficit[1].

References:
[1]. Saugstad OD, et al. Hypoxanthine as an indicator of hypoxia: its role in health and disease through free radical production. Pediatr Res. 1988 Feb;23(2):143-50.