Is an increased PaO₂ in a normobaric state safe in acute CO poisoning?

Our objective was to determine how much PaO₂ levels increase after normobaric oxygen (NBO) therapy and whether NBO therapy exerts therapeutic effects regardless of the PaO₂ level. We suggest the optimal PaO₂ level to use during NBO therapy for the acute treatment of carbon monoxide (CO) poisoning. This retrospective study included 311 patients who received oxygen administration after CO poisoning and had a measurable PaO₂ level upon arrival. Baseline characteristics, clinical courses and long-term neurological outcome were collected and compared. The PaO₂ level upon arrival was 192 (161-225) mm Hg, and 272 (87.5%) of the patients presented with hyperoxia. The incidence of poor long-term neurological outcome was 11.3% at a median follow-up period of 35 months. PaO₂ levels upon arrival were higher in patients with good long-term neurological outcome than in those with poor outcome. The incidence of poor long-term neurological outcome was significantly dependent on the PaO₂ level when patients were stratified at 100-mm Hg increments. A multivariate regression analysis showed that PaO₂ levels, when considered a continuous, interval or ordinal variable, were associated with long-term neurological outcome in separate models. According to the three models, a PaO₂ level of 200-300 mm Hg has the lowest risk of poor long-term neurological outcome. The results of the analysis of the predicted probability of poor long-term outcome according to the PaO₂ level exhibited a U-shaped curve. Further large-scale studies are needed to confirm the association between 200-300 mm Hg of PaO₂ and long-term neurological outcome and evaluate the impact of PaO₂ levels above 300 mm Hg on acute CO poisoning outcome.