Benefits and risks of oxygen therapy during acute medical illness: Just a matter of dose!

Oxygen therapy is used to reverse hypoxemia since more than a century. Current usage is broader and includes routine oxygen administration despite normoxemia which may result in prolonged periods of hyperoxemia. While systematic oxygen therapy was expected to be of benefit in some ischemic diseases such as stroke or acute myocardial infarction, recent randomised controlled trials (RCTs) have challenged this hypothesis by showing the absence of clinical improvement. Although oxygen is known to be toxic at high inspired oxygen fractions, a recent meta-analysis of RCTs revealed the life-threatening effect of hyperoxemia, with a dose-dependent relationship. Several recommendations have therefore been updated: (i) to monitor peripheral oxygen saturation (SpO) as a surrogate for arterial oxygen saturation (SaO); (ii) to initiate oxygen only when the lower SpO threshold is crossed; (iii) to titrate the delivered oxygen fraction to maintain SpO within a target range; and (iv) to stop supplying oxygen when the upper limit of SpO is surpassed, in order to prevent hyperoxemia. The lower and upper limits of SpO depend on the presence of risk factors for oxygen-induced hypercapnia (Chronic obstructive pulmonary disease, asthma, and obesity-associated hypoventilation). For patients at risk, oxygen therapy should be started when SpO is≤88% and stopped when it is>92%. For patients without risk factors, oxygen therapy should be started when SpO is≤92% and stopped when it is >96%. High-flow oxygen should only be used in a few diseases such as carbon monoxide poisoning, cluster headaches, sickle cell crisis and pneumothorax.