Frequency of Hypoxemia and Hyperoxemia and Their Association With 90-Day Mortality in Critically Ill Oncology Patients: A Retrospective Observational Study

Background: Oxygen therapy is a cornerstone of critical care management. Both inadequate oxygenation and excessive oxygen exposure have been associated with adverse physiologic effects and poorer clinical outcomes. While hypoxemia may lead to tissue hypoxia and organ dysfunction, hyperoxemia has been implicated in oxidative stress and cellular injury. This study aimed to determine the frequency of hypoxemia and hyperoxemia among critically ill patients and evaluate their association with 90-day mortality. Methods: A retrospective observational study was conducted, including 228 critically ill oncology patients admitted to the intensive care unit (ICU) or high-dependency unit (HDU). The frequency of hypoxemia and hyperoxemia was determined using predefined criteria. Ninety-day mortality was the primary outcome. Associations between oxygenation abnormalities and mortality were evaluated using chi-square and Fisher's exact tests. Univariable and multivariable logistic regression analyses were performed to identify independent predictors of mortality after adjustment for age, sex, and ICU/HDU admission status and oxygenation variables. Results: A total of 228 critically ill patients were included in the analysis, with 90-day mortality observed in 126 patients (55.3%). There were no significant differences in age or sex between survivors and non-survivors. Patients who died were more frequently admitted to the ICU than the HDU and had a significantly higher prevalence of hypoxemia. Hyperoxemia was numerically more common among non-survivors. Mortality was markedly higher among patients with hypoxemia compared with those without, and was also higher among hyperoxemic patients. On univariable analysis, ICU admission, hypoxemia, and hyperoxemia were all associated with increased odds of 90-day mortality. After adjustment for age, sex, ICU/HDU status, and oxygenation status, increasing age, ICU admission, and hypoxemia remained independently associated with mortality, whereas hyperoxemia was not. Male sex was not associated with mortality. However, association with severe illness scores like Acute Physiology and Chronic Health Evaluation (APACHE) and Sequential Organ Failure Assessment (SOFA) scores was not analyzed and remains a major limitation of the study. Conclusion: Hypoxemia was common among critically ill patients and associated with increased 90-day mortality. Mortality increased progressively with worsening hypoxemia severity. Hyperoxemia demonstrated an association with mortality on unadjusted analysis but was not independently associated after adjustment. However, these findings should be interpreted with caution because illness severity scores were unavailable and could not be incorporated into the analysis.