Comparison of the automatised and the optimised carbon monoxide rebreathing methods

Abstract

Recently, a new automated carbon monoxide (CO) rebreathing method (aCO) to estimate haemoglobin mass (Hb_mass) was introduced. The aCO method uses the same CO dilution principle as the widely used optimised CO rebreathing method (oCO). The two methods differ in terms of CO administration, body position, and rebreathing time. Whereas with aCO, CO is administered automatically by the system in a supine position of the subject, with oCO, CO is administered manually by an experienced operator with the subject sitting. Therefore, the aim of this study was to quantify possible differences in Hb_mass estimated with the two methods. Hb_mass was estimated in 18 subjects (9 females, 9 males) with oCO using capillary blood samples (oCOc) and aCO taking simultaneously venous blood samples (aCOv) and capillary blood samples (aCOc). Overall, Hb_mass was different between the three measurement procedures (F = 57.55, p < .001). Hb_mass was lower (p < .001) for oCOc (737 g ± 179 g) than for both aCOv (825 g ± 189 g, −9.3%) and aCOc (835 g ± 189 g, −10.6%). There was no difference in Hb_mass estimated with aCOv and aCOc procedures (p = .12). Three factors can likely explain the 10% difference in Hb_mass: differences in calculations (including a factor for myoglobin flux), body position (distribution of CO in blood circulation) during rebreathing, and time of blood sampling. Moreover, the determination of Hb_mass with aCO is possible with capillary blood sampling instead of venous blood sampling.

Keywords:

• Haemoglobin mass
• CO rebreathing methods
• carboxyhaemoglobin
• erythrocytes
• kinetics

Acknowledgements

There was no external financial support. We would like to thank Rilana Perl for her great help with the study organisation and recruitment, and all the participants for their time and attendance in the study. We thank Dr. med Christian Protte for his medical support during the study and Nicole Winistörfer and Nadège Jeandupeux for their help with venous blood sampling. The authors thank Severin Trösch for his contributions to the study design and preparatory analysis.

Disclosure statement

The authors declare that they have no conflicts of interest.