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The following is a summary of “Inverse linear association between blood haemoglobin and oxygen saturation accuracy measured by pulse oximetry: a cross-sectional analysis in individuals with COVID-19 infection,” published in the November 2024 issue of Emergency Medicine by Crooks et al. 

Researchers conducted a retrospective study analyzing the association between blood hemoglobin levels and pulse oximetry error in measuring blood oxygen saturation.   

They assessed all adult patients admitted to the hospital with suspected or confirmed COVID-19 infection from February 2020 to December 2021 who had drawn arterial blood gases (ABGs). The Pulse oximetry readings were compared with arterial saturation on ABGs, and measurement error was determined based on ABG hemoglobin levels. A secondary analysis was conducted among patients with venous hemoglobin drawn within 24 hours and compared the measurement error between ABG arterial saturation and pulse oximetry readings among those with normal (≥150 g/L) and low (<70 g/L) hemoglobin levels.   

The results showed that the analysis included 5,922 paired oxygen saturation measurements from 3,994 patients with concurrent hemoglobin measurements by ABG. A 1 g/L decrease in blood hemoglobin was associated with a 0.021% (95% CI: +0.008% to +0.033%) increase in the measurement error (towards a falsely elevated reading). Among the 1,086 patients with venous hemoglobin measurements, a 0.055% (95% CI: +0.020% to +0.090%) increase in oxygen saturation measurement error was observed per 1 g/L decrease in blood hemoglobin. Thus, the measurement error was higher in individuals with anemia than in those with normal hemoglobin levels.   

Investigators concluded a decrease in blood hemoglobin level was linked with an increased error in pulse oximetry measurements, leading to falsely elevated oxygen saturation readings, particularly in patients with COVID-19, hemorrhage, or anemia. 

Source: emj.bmj.com/content/early/2024/11/13/emermed-2023-213712