Abstract
Background: Pulse oximeters are routinely used in community and hospital settings worldwide as a rapid, non-invasive, and readily available bedside tool to approximate blood oxygenation. Potential racial biases in SpO2 measurements may influence the accuracy of pulse oximetry readings and impact clinical decision making. We aimed to assess whether the accuracy of oxygen saturation measured by peripheral pulse oximetry (SpO2), relative to arterial blood gas (SaO2), varies by ethnicity.
Methods: In this large retrospective observational cohort study covering four NHS Hospitals serving a large urban population in Birmingham, consecutive patients admitted to hospital requiring oxygen therapy were identified by electronic patient records. For each spell, the first available pair of SpO2 and SaO2 measurements taken within an interval of less than 20 minutes were identified and included in the analysis. The differences between SpO2 and SaO2 measurements, were compared across self-identified groups of ethnicities. These differences were subsequently adjusted for age, sex, bilirubin, systolic blood pressure, carboxyhaemaglobin saturations and the time interval between SpO2 and SaO2 measurements.
Findings: Paired O2 saturation measurements from 16818 inpatient spells between 1st January 2017 and 18th February 2021, were analysed. The cohort self-identified as being of White (81.2%), Asian (11.7%), Black (4.0%), or Other (3.2%) ethnicities. Across the cohort, SpO2 was significantly higher than SaO2 (median: 98% vs. 97%, p<0.001), with a median difference of 0.5 percentage points (pps). However, the size of this difference varied considerably with the magnitude of SaO2, with SpO2 overestimation by a median of 3.8pp for SaO2 values <90% but underestimating by a median of 0.4pp for an SaO2 of 95%. The differences between SpO2 and SaO2 were also found to vary significantly by ethnicity, with this difference being 0.8pp (95% confidence interval: 0.6-1.0) greater in those of Black vs. White ethnicity. These differences resulted in 6.1% vs. 8.7% of White vs. Black patients classified as normoxic on SpO2 who were hypoxic on the gold standard SaO2 reading (p=0.007).
Interpretation: Pulse oximetry tends to overestimate O2 saturation, and this is more pronounced in patients of Black ethnicity. Prospective studies are urgently warranted to assess the impact of ethnicity on the accuracy of pulse oximetry, to ensure care is optimised for all.
Methods: In this large retrospective observational cohort study covering four NHS Hospitals serving a large urban population in Birmingham, consecutive patients admitted to hospital requiring oxygen therapy were identified by electronic patient records. For each spell, the first available pair of SpO2 and SaO2 measurements taken within an interval of less than 20 minutes were identified and included in the analysis. The differences between SpO2 and SaO2 measurements, were compared across self-identified groups of ethnicities. These differences were subsequently adjusted for age, sex, bilirubin, systolic blood pressure, carboxyhaemaglobin saturations and the time interval between SpO2 and SaO2 measurements.
Findings: Paired O2 saturation measurements from 16818 inpatient spells between 1st January 2017 and 18th February 2021, were analysed. The cohort self-identified as being of White (81.2%), Asian (11.7%), Black (4.0%), or Other (3.2%) ethnicities. Across the cohort, SpO2 was significantly higher than SaO2 (median: 98% vs. 97%, p<0.001), with a median difference of 0.5 percentage points (pps). However, the size of this difference varied considerably with the magnitude of SaO2, with SpO2 overestimation by a median of 3.8pp for SaO2 values <90% but underestimating by a median of 0.4pp for an SaO2 of 95%. The differences between SpO2 and SaO2 were also found to vary significantly by ethnicity, with this difference being 0.8pp (95% confidence interval: 0.6-1.0) greater in those of Black vs. White ethnicity. These differences resulted in 6.1% vs. 8.7% of White vs. Black patients classified as normoxic on SpO2 who were hypoxic on the gold standard SaO2 reading (p=0.007).
Interpretation: Pulse oximetry tends to overestimate O2 saturation, and this is more pronounced in patients of Black ethnicity. Prospective studies are urgently warranted to assess the impact of ethnicity on the accuracy of pulse oximetry, to ensure care is optimised for all.
| Original language | English |
|---|---|
| Publisher | medRxiv |
| DOIs | |
| Publication status | Published - 26 Nov 2021 |
Bibliographical note
Funding:This work was supported by PIONEER, the Health Data Research UK (HDR-UK) Health Data Research Hub in acute care. HDR-UK is an initiative funded by the UK Research and Innovation, Department of Health and Social Care (England) and the devolved administrations, and leading medical research charities.