Pathophysiological aspects of oxygen, hypoxia and free radical oxidation in critical conditions

Oxygen is the main regulator of metabolic processes in the body not only in the context of normal physiology, but also in the development of various critical conditions.

In recent years, the problem of pathogenesis of a number organs' and systems' diseases has been enriched by knowledge of the mechanism of damage to cellular structures. Oxygen turned out to be the main factor of damage — the very oxygen, due to the lack of which cell death occurs. It turned out that the so-called reactive oxygen species having an unpaired electron have a biological effect, which, depending on the concentration, can be regulatory or, conversely, toxic. Accordingly, interest has also been aroused in compounds that normally prevent the toxic effect of reactive oxygen species — antioxidants. Today it is generally recognized that oxidative stress plays an important and possibly a key role in the pathogenesis of critical conditions. Thus, on the one side, excessive production of free radicals is considered as one of the manifestations of the body's protective reaction to the effects of various environmental factors and living conditions (infections, injuries, toxins, ionizing radiation, physical stress, hypothermia, hypoxia, various types of stress), on the other ― increased production of free radicals quickly leads to irreversible damage: destruction of the erythrocytes' membranes with subsequent hemolysis, transformation of hemoglobin into methemoglobin, DNA damage, desensitization of plasma membrane receptors, inactivation of various hormones and enzymes, including antiradical and antiperoxide protection enzymes.

The problem of using oxygen in critical conditions is currently widely discussed in the periodical literature with an emphasis on the oxygen concentrations used in patients, both in operating rooms and in intensive care units. Oxygen used in the intensive care of acute respiratory failure and hypoxia should have a certain concentration range. The toxic effects of oxygen can occur with its prolonged use in high concentrations, which causes not only its direct toxic effect on the lungs, but also in the potentiation of the activation of free radical oxidation and excessive production of reactive oxygen species.

The review presents current data on the physiological role of oxygen, its participation in metabolic processes against the background of inflammation, hypoxia and under conditions of activation of free radical oxidation processes. The recent approach to oxygen therapy and the research data presented in the review urge to relate to oxygen as a drug in order to avoid manifestations of its toxic effects.