Predictive Value of P50 in the Clinical Outcome of the Patients with Severe COVID-19 Pneumonia: A Retrospective Cohort Study

Background: The oxygen tension at half-saturation (P50) was found to be increased in patients with respiratory distress. However, the roles of P50 calculated upon hospital admission in predicting the prognosis of severe COVID-19 patients are not well-investigated. Thus, this study aimed to investigate whether P50 values obtained from hypoxic severe COVID-19 patients upon admission were associated with a later need of invasive mechanical ventilation (IMV). This study also aimed at finding independent predictors of IMV. Materials and Methods: 151 patients with confirmed severe COVID-19 were enrolled in this study between August and December 2020. Overall, 63 (41.7%) progressed to IMV, and 88(58.2%) did not need IMV. Demographic data, clinical outcome, and laboratory measurements were recorded, and P50 was calculated. P50 that discriminated patients required IMV and patients did not require IMV was determined using the ROC curve. The risk factors for the need for IMV were identified through logistic regression. Results: The calculated P50 of all patients was higher than the normal value (P<0.005). Moreover, P50 was significantly higher in patients who required IMV (P=0.002). ROC curve verified the discriminatory ability of P50, providing an area under the ROC curve of 0.647(95%CI 0.558-0.736; P=0.002) for a cutoff of 29.29mmHg. Calculated P50≥29.29mmHg was a risk factor for the need of IMV (OR=3.306, 95%CI 1.676-6.525; P=0.001). In multivariate analysis, the independent predictors of the need for IMV were older age, male sex, high P50, high aspartate transaminase, and low PO2 (P<0.05). Conclusion: Calculated P50 on hospital admission might serve as a promising predictor of IMV in severe COVID-19.