Evaluating Venous Blood Gas Po2 as an Early Marker of Illness Severity in ED Patients

We conducted a prospective observational study of adult ED patients who had a VBG obtained as part of routine clinical care. Demographic, physiologic, and laboratory data were collected at the time of ED presentation. Early clinical severity was defined as intensive care unit (ICU) admission, in-hospital mortality, vasopressor initiation, or requirement for positive-pressure ventilation (PPV) within 48 hours. Secondary analyses assessed the relationship between venous pO₂ and lactate levels and evaluated whether the addition of venous pO₂ improved prediction of adverse outcomes beyond lactate alone. Associations were assessed using univariate comparisons and multivariable logistic regression.

Venous blood gas (VBG) analysis is frequently utilized in the Emergency Department (ED) as a rapid, less invasive alternative to arterial blood gas sampling. While venous pH, pCO₂, and lactate have established clinical utility, the prognostic significance of venous partial pressure of oxygen (pO₂) remains poorly defined. Given the physiologic relationship between oxygen extraction and tissue perfusion, venous pO₂ has been hypothesized as a potential marker of early illness severity. This study aimed to evaluate whether VBG pO₂ is associated with early adverse clinical outcomes and whether it provides incremental prognostic value beyond lactate.

Among 932 patients with analyzable VBGs, 878 had paired venous pO₂ and lactate values available for secondary analyses. Median venous pO₂ was 33 mmHg (IQR 25–44), with approximately 40% of patients demonstrating pO₂

In this prospective ED cohort, peripheral venous pO₂ was not associated with early clinical severity and did not provide meaningful incremental prognostic value beyond lactate. Despite physiologic plausibility, venous pO₂ does not appear to enhance early risk stratification in ED patients.