The impact of MetHb and COHb on SpO2 measured with pulse oximetry. (a) Blood MetHb vs. SpO2 and blood Hb O2 saturation (O2Hb). Data extracted from Barker et al. [86]. (b) Blood COHb vs. SpO2 and blood O2Hb saturation. Data extracted from Barker et al. [87]. In both studies, measurements were made on dogs; the inspired O2 fraction (FIO2) was 1, SpO2 was measured on the tongue with a pulse oximeter (Nellcor N-100, USA) and COHb, MetHb and O2Hb saturation with a CO-oximeter (IL-282, Instrumentation Laboratories, Bedford, MA, USA). The figures show data extracted from the original figures of the respective publications.