Supplementary oxygen for nonhypoxemic patients: O2 much of a good thing?

... the aim of oxygen therapy should be to increase the delivery of oxygen rather than to reach any arbitrary concentration in the arterial blood.EJM Campbell [1]Is administration of oxygen, the most widely prescribed drug in the formulary, free of risks to nonhypoxemic patients with regional ischemia? Hyperoxia marginally increases the arterial blood oxygen content (CaO2), theoretically increasing tissue oxygen delivery (DO2) assuming no reduction in tissue blood flow. However, oxygen causes constriction of the coronary, cerebral, renal and other key vasculatures - and if regional perfusion decreases concomitantly with blood hyperoxygenation, one would have a seemingly paradoxical situation in which the administration of oxygen may place tissues at increased risk of hypoxic stress. Any tissue damage in the course of oxygen administration would plausibly be attributed to the underlying disease process. Ascribing hypoxic damage to oxygen administration is counter-intuitive and is difficult to accept without a receptive mindset. Considering the ubiquity of oxygen therapy, the continued low threshold for its administration, and the widespread belief that its use is justified and safe [2,3], we believe it is important to revisit the arguments made to justify the status quo.Owing to the vasoconstrictor effects on the coronary, cerebral, renal and other key vasculatures, there are many scenarios in which administration of oxygen decreases the perfusion to vital organs to a greater extent than the small increase in CaO2, thereby actually reducing DO2. The calculated CaO2 increases with normobaric hyperoxia (assuming all hemoglobin is already saturated) by only 0.03 ml/l per mmHg. With increases in alveolar PaO2 from 100 to 600 mmHg, CaO2 increases by 15 ml/l, or about ~7.5% assuming a hemoglobin concentration of 150 g/l.In healthy adults, hyperoxia decreases cerebral blood flow by 11 to 33% [4,5]. Administration of high oxygen concentrations is therefore likely to decrease