Abstract

Objective: To evaluate agreement between simultaneously obtained peripheral venous and Arterial Blood Gas (ABG) values (pH, pCO2, pO2, HCO3-) in emergency department patients and to quantify the incremental value of applying published and newly derived conversion (“arterialization”) formulas with respect to Clinical Laboratory Improvement Amendments (CLIA) acceptability.
Methods: This prospective study enrolled 105 adult patients requiring ABG analysis (May-September 2016). Simultaneous arterial and peripheral venous samples were analyzed on a single blood gas analyzer. Paired comparisons used paired t tests, Pearson correlation, and Bland-Altman analysis. Linear regression (multivariable for pO2) generated new formulas; performance was compared with previously published models. The proportions of raw venous and arterialized (formula-adjusted) venous results outside CLIA limits were calculated.
Result: Venous and arterial values differed systematically but showed strong linear relationships for pH, pCO2, and HCO3-, while the association for pO2 was only moderate before adjustment. Applying conversion formulas materially improved clinical acceptability: For example, the proportion of venous pCO2 values outside CLIA limits was cut from nearly one half of paired samples to roughly one eighth, and venous pH discordance similarly fell by more than half. Bicarbonate exhibited minimal bias and high concordance even before adjustment, with only modest incremental gain. Although a multivariable equation noticeably increased correlation for pO2, the limits of agreement remained too wide to justify substituting venous-based estimates for direct arterial oxygen assessment.
Conclusion: Simple conversion formulas substantially improve venous estimation of arterial pH, pCO2, and HCO3- and may reduce the need for some arterial punctures in emergency practice. Venous-based estimation of pO2 remains unreliable and should not replace direct arterial measurement for assessing oxygenation.

Keywords:Arterial blood gas; Venous blood gas; Conversion formula; Agreement; Emergency department; Bicarbonate