Oxygen Variations—Insights into Hypoxia, Hyperoxia and Hyperbaric Hyperoxia—Is the Dose the Clue?

Abstract

Molecular oxygen (O2) is one of the four most important elements on Earth (alongside carbon, nitrogen and hydrogen); aerobic organisms depend on it to release energy from carbon-based molecules. The concentration of oxygen in the atmosphere is 20.93–20.95% (209–460 ppm), but this has fluctuated markedly throughout geological history. It stabilized within a habitable range, Between ~15% and 35%, which has been maintained from the Cambrian period 540 million years ago until today [1]. The history of the use and the study of oxygen is of great interest, yet we firmly believe that it has not yet reached a final point. Nowadays, the therapeutic use of oxygen is not only limited to restoring hypoxia, but several newly developed approaches use oxygen not only as a “restoring agent” [2] but also as a potent stimulus [3]. Salvagno et al. based their review on the paradoxical response of the intermittent shift between hyperoxic–normoxic exposure, which was shown to enhance erythropoietin production and raise hemoglobin levels with numerous different potential applications in many fields of therapy as a new strategy for surgical preconditioning aimed at frail patients and prevention of postoperative anemia. They summarize the physiological processes behind the proposed “normobaric oxygen paradox”, focusing on the latest scientific evidence and the potential applications for this strategy [4,5].