Hyperoxia: At what level of SpO₂ is a patient safe? A study in mechanically ventilated ICU patients

Concerns have been expressed regarding a possible association between arterial hyperoxia and adverse outcomes in critically ill patients. Oxygen status is commonly monitored noninvasively by peripheral saturation monitoring (SpO₂). However, the risk of hyperoxia above specific SpO₂ levels in critically ill patients is unknown. The purpose of this study was to determine a threshold value of SpO₂ above which the prevalence of arterial hyperoxia distinctly increases.

This is a cross-sectional study in adult mechanically ventilated intensive care patients in a tertiary referral center. In 100 patients, we collected 200 arterial blood gases (ABG) and simultaneously registered SpO₂ levels, as well as hemodynamic and ventilation parameters and vasoactive medication. Patients under therapeutic hypothermia were excluded.

The risk of arterial hyperoxia, defined as PaO₂>100mmHg or >125mmHg, was negligible when SpO₂ was ≤95% or ≤96%, respectively. The majority (89% and 54%, respectively for PaO₂>100mmHg and 125mmHg) of ICU patients with SpO₂ of 100% had arterial hyperoxia. The relation between SpO2 and PaO₂ was not clearly affected by hemodynamic or other clinical variables (pH, pCO₂, body temperature, recent blood transfusion).

In critically ill patients, the prevalence of arterial hyperoxia increases when SpO₂ is >95%. Above this saturation level, supplemental oxygen should be administered with caution in patients potentially susceptible to adverse effects of hyperoxia.