Critical care physicians often fight to keep up oxygen levels in their patients with respiratory failure and ARDS to to support an energy metabolism that can sustain life. In neonates, impressive studies have long ago shown that oxygen should never be given in excess of what is needed to sufficiently load hemoglobin (in order to prevent, e.g. retinopathy). In the past decade, researchers have put a lot of efforts in defining the optimal range of oxygen saturation in neonates.
Until recently, in adults, the prevailing attitude seems to have been
„More oxygen cannot hurt!“
In spite of studies indicating deleterious effects of hyperoxia dating back to the 1940s, prevention of hyperoxia – and oxygen toxicity – in adults has never been on the list of top priorities.
The picture seems to be changing, however. In 2012, a retrospective study suggested deterioration of pulmonary outcomes to be associated with prolonged exposure to high fractions of inspired oxygen.
Now, an investigators’ group from Australia, New Zealand, and France have published a prospective pilot study (Panwar et al: AJRCCM 2016, 193-1 pp.43-51) supporting the feasibility of applying lower target oxygen saturation (SpO2 88-92%) to ventilated patients, paving the way for larger studies which I expect to show important patient benefit from being stingy on the FiO2 settings.
There is a perception that oxygen therapy is safe. This perception of safety, however, is now being challenged by the increasing recognition of the potential harm of excessive levels of inspiratory oxygen (FiO2)
The attitude of „more oxygen cannot hurt“ is definitely replaced by a more cautious approach. Although there are no proven benefits of permissive hypoxemia yet, and a lower limit has not been defined, hyperoxemia associated with tissue hyperoxia should clearly be avoided.
For any study in ventilated patients, this means the sponsor has to set oxygenation goals, monitor adherence to these goals, and give feedback to investigators in order to corroborate adherence.
Since it should go without saying that close control of applied tidal volumes in clinical studies of ventilated patients is demonstrated (see figure below), the additional effort to keep an eye on avoiding unnecessarily high oxygen saturation should be minimal.
Figure from Taut et al (2011) J Clin Trials 1, 101-106
If done efficiently, this effort for better patient care will even pay off – by stronger buy-in of study teams to an ethical study approach, respect and appreciation of the sponsor’s high standards, and increased scientific validity of the study results.
Exposing patients to potentially toxic oxygen levels causing hyperoxemia and tissue hyperoxia can no longer be justified.
View related post by Friedemann on why ARDS studies notoriously failed during the last decades, and on the promising results of the Lung Safe Study