Measured fraction of carboxyhaemoglobin depends on oxygen saturation of haemoglobin

Abstract

The use of the OSM3 oximeter for measurement of the fraction of carboxyhaemoglobin (F COHb) in blood allows for estimation of total circulating haemoglobin mass (Hb_tot) by using the carbon monoxide rebreathing method. To ensure high accuracy of Hb_tot estimation, potential sources of analytical errors should be identified and adjusted for. Based on observed differences in results of measured F COHb between simultaneously sampled, arterialized and venous blood samples we investigated the influence of haemoglobin oxygen saturation (s O₂) on results of measured F COHb. Blood from nine healthy non-smokers was tonometered with gas mixtures containing 94% N₂ or air and 6% CO₂. The resulting oxygenated and deoxygenated specimens were mixed in different proportions to obtain varying s O₂ values in the same blood. s O₂, fractions of dyshaemoglobins, p O₂, p CO₂ and pH were measured at each step. F COHb was significantly (pomega 0.001) higher in oxygenated (median, range: 0.6%, 0.4- 0.9%) compared to deoxygenated (- 0.2%, - 0.5- 0.0%) blood. Regression analysis identified the s O₂ as the most important factor explaining 86% of the variance in observed changes in F COHb. The observed s O₂ effect has important implications on calibration procedure of OSM3, accuracy of measured F COHb, and F COHb dependent calculations such as estimation of Hb_tot and related quantities. If the highest accuracy of F COHb measurement is needed, an s O₂ effect on results of measured F COHb has to be considered and adjusted for.

• Words Analytical Error Bias Blood Gases Hemoximeter