Hypercapnia as the influencing factor of pulse oximetry

To the Editors:

We would like to comment on the recently published study by Muñoz et al. 1, which analysed accuracy and precision of pulse oximetry at different carbon dioxide arterial tension (P_a,CO2) levels. Although the paper investigates an interesting hypothesis, significant limitations should be addressed.

The most important limitation is that the reported mean P_a,CO2 of 45.3±8.0 mmHg does not exactly reflect hypercapnia. As 45.0 mmHg is an accepted boundary …