Arterial oxygen status determined with routine pH/blood gas equipment and multi-wavelength hemoximetry: Reference values, precision, and accuracy

Abstract

We measured pH, pCO₂, pO₂, oxygen saturation, total hemoglobin concentration, and fractions of carboxy-and methemoglobin in arterial blood samples from 35 healthy adults. We used a new algorithm to calculate active hemoglobin concentration, total oxygen concentration, actual half-saturation tension, 2,3-di-phospho-glycerate concentration, estimated functional shunt, oxygen extraction tension p_x (for extracting 2.3 mmol of oxygen per liter of blood, values below 4.5 kPa indicating risk of tissue hypoxia), and the oxygen compensation factor Q_x (the factor by which the cardiac output should rise to maintain a normal mixed venous pO₂ of 5.0 kPa, factors above 1.5 indicating an extra burden on the heart). Analytical precision was evaluated by duplicate determinations. The accuracy of the half-saturation tension was evaluated by comparison with values for simultaneously drawn venous blood, the accuracy of the calculated concentration of 2,3-diphosphoglycerate by comparison with direct enzymatic measurements. We conclude that all the variables may be determined with sufficient accuracy and precision in healthy adults, provided the oxygen saturation is less than 0.97 and the measurements are performed according to the highest state of the art.

Key Words:

• 2,3-diphosphoglycerate
• hemoglobin-oxygen affinity
• oxygen saturation
• oxygen tension.