Permissive hypoxemia/conservative oxygenation strategy: Dr. Jekyll or Mr. Hyde?

Oxygen is one of the essentials required for sustaining life, which plays an important role in human medical history. It has become a routine therapy for critically ill patients, and the assessment and administration of oxygen in the ICU gained more and more attention (1,2). Both hypoxia and hyperoxia is related to adverse outcome. de Jonge et al. demonstrated that there was a U-shaped relationship between PaO₂ and in-hospital mortality, the lowest of the mortality being at PaO₂ values of 110–150 mmHg; mortality sharply increased both at PaO₂ values <67 mmHg and >225 mmHg (3). Nowadays, the “double-edged sword” character of oxygen is well established. On one hand, the hypoxia result in the imbalance between O₂ supply and requirements, which could induce tissue hypoxia and cell death. On the other hand, the presence of hyperoxia enhances reactive oxygen species (ROS) and oxidative stress, which cause alveolar and cell damage. The benefit/harm ratio of oxygen therapy is determined by the O₂ dose, exposure duration, and underlying diseases. To reduce the potential risks of hyperoxia, a lower oxygenation targets may be acceptable in critically ill patients. A tolerable low SaO₂ also termed as permissive hypoxemia/conservative oxygenation strategy. Generally, the permissive hypoxemia strategy aims for an SaO₂ between approximately 85% and 95%, which always use in the ARDS patients and preterm infants (4,5).