Friday, 29 March, 2024
HomeA Practitioner's Must ReadPulse oximeters deliver unreliable readings across ethnic groups

Pulse oximeters deliver unreliable readings across ethnic groups

A non-invasive test with a pulse oximeter provided false readings of nearly 7% higher in a group of mixed race patients with COVID-19, compared with white patients at just more than 3%, found a study in the European Respiratory Journal.

The difference between the readings also increased in the clinically important range of 85% to 89%, when many clinical decisions are made.

There were also falsely high readings in patients with both black and Asian ethnicity, which could delay patients receiving the best and most timely treatment for the virus. This showed that the severity of COVID-19 pneumonia can be difficult to assess across different ethnic groups, say researchers.

Pulse oximetry measures the oxygen saturation level of the blood, and can rapidly detect even small changes in oxygen levels. These levels show how efficiently blood is carrying oxygen to the extremities furthest from the heart, including the arms and legs. Medical professionals routinely use them in primary care and critical care settings, like emergency rooms or hospitals, to monitor the clinical status of their patients.

The light wave transmission that this technology uses is modified by skin pigmentation and may vary by skin colour. A recent study reported different outputs in patients with black skin compared with patients with white skin, which has the potential to adversely affect patient care. This led to the US Food and Drink Administration (FDA) releasing an expression of concern about the accuracy of pulse oximeters in 2021, which led to the current study.

The study was delivered by a consortium of multidisciplinary teams from the University of Nottingham and Nottingham University Hospitals NHS Trust. They made use of the electronic datasets that are collected for clinical use in real time, but archived and available to answer important clinical questions and improve both patient care and patient safety in the future. The NUH COVID-19 Patient Safety Database is anonymised to allow lessons to be learned without compromising individual patient confidentiality. The team included clinicians, managers, statisticians, computer analysts, software coders and data warehouse archivists.

The team from Nottingham used data from patients with COVID-19 infection to look at the difference in blood oxygen levels as measured by pulse oximetry and arterial blood gas tests, spilt into different ethnic groups over a wide range of oxygen saturations. Arterial blood gas tests measure the levels of oxygen in the blood from an artery, and represent the gold standard measurement for oxygen levels.

The team used electronic data for patients admitted to Nottingham University Hospitals NHS Trust between February 2020 and September 2021 with COVID-19 infection. Pulse oximetry measurements with a paired blood gas measurement within a half an hour window were compared.

Mean differences between pulse oximetry and blood gas oxygen saturations were recorded by ethnicity of white, mixed, Asian, and black patients, and were also split up by level of oxygen saturation as measured by arterial blood gases. There were differences in oxygen saturations (amounts of oxygen in the blood), between the pulse oximetry arterial blood gas readings in all groups. The highest difference was in the mixed ethnicity group, which was nearly 7% higher in the oximetry reading, with the lowest in the white group at 3.2% higher than the true measurement from arterial blood gases. A reading of 5.4% higher using pulse oximetry was found in the black group and 5.1% higher in the Asian population.

The difference between the readings also increased in the clinically important range of 85% to 89%, when many clinical decisions are made. Mean values as measured by pulse oximeter were higher than reality in individuals with a recorded black and Asian ethnicity, compared with white participants.

The findings of the research are important as high levels of skin pigmentation are associated with ethnic groups who have a poorer outcome from COVID-19 infection, and would require the most accurate oxygen measurements available to deliver the most appropriate and timely treatment.

Dr Andrew Fogarty, from the School of Medicine at the university and the lead author of the study, said: “These data build on what we know, which is that patients with darker skin have less accurate oxygen measurements using the pulse oximeters. Any error of measurement of oxygen levels will make assessing the severity of COVID-19 infection more difficult, and may delay delivery of timely medical care. We are now exploring the impact of this on clinical outcomes to see if it may have led to any issues in escalating treatment intensity for our patients.”

Study details

Pulse oximeters' measurements vary across ethnic groups: An observational study in patients with Covid-19 infection

Colin J Crooks, Joe West, Joanne R Morling, Mark Simmonds, Irene Juurlink, Steve Briggs, Simon Cruickshank, Susan Hammond-Pears, Dominick Shaw, Timothy R Card, Andrew W Fogarty.

Published in European Respiratory Journal, 2022

 

Abstract

The pulse oximeter provides regular non-invasive measurements of blood oxygenation and is used in a wide range of clinical settings. The light wave transmission that this technology uses is modified by skin pigmentation and thus may vary by skin colour. A recent study of paired measures of oxygen saturation from pulse oximetry and arterial blood gas reported differing outputs in patients with black skin compared to patients with white skin that has the potential to adversely impact on patient care. The natural history of COVID-19 infection is modified by ethnic group and individuals with more pigmented skin generally have a higher risk of severe disease. We have used data from patients with COVID-19 infection to explore the differential in difference of blood oxygen levels as measured by pulse oximetry and arterial blood gases stratified by different ethnic groups over a wide range of oxygen saturations. We used routinely collected electronic data for patients admitted to Nottingham University Hospitals NHS trust between 1 February 2020 and 5 September 2021 with either suspected or confirmed SARS-CoV-2. Pulse oximetry measurements with a paired blood gas measurement within a 30-min time window were used as the primary outcome. A 10-min window between paired samples was assessed as a sensitivity analysis. Data from Intensive Care Units were not available. Mean differences between oximetry and blood gas were stratified by recorded ethnicity of white, mixed, Asian, black and also stratified by level of oxygen saturation as measured by arterial blood gases. A mixed effect linear models of the difference between oximetry and blood gas oxygen saturation by ethnicity (either white or black, Asian or mixed ethnicity) using patient as a random intercept were fitted. Due to the small numbers of individuals labelled as black, Asian and mixed ethnic group, a final comparison of these combined categories was compared with the much larger white ethnic group for a final analysis to generate a simple output that can be disseminated to increase clinical awareness of these issues, while concurring with current guidance on describing and reporting ethnicity.

Analyses were performed using R statistical software. NUH Clinical Effectiveness Team audit gave approval for these analyses. We identified 2997 eligible patients with 5374 paired oxygen saturations recorded in their routine electronic observations within 30 min of an arterial blood gas. There were differences in the mean difference between oxygen saturations as measured by pulse oximetry compared to arterial blood gas (p=0.02, ANOVA) with the highest differential in the Mixed ethnic group (+6.9%; 95% Confidence Interval CI: −21.9 to +35.8) and the lowest in the white group (+3.2%; 95% CI: −22.8 to +29.1), with those in the black group (+5.4; 95% CI: −25.9 to +36.8) and Asian group (+5.1%; 95% CI: −23.8 to 34.0) having intermediate differentials. A sensitivity analysis restricting to a 10-min window did not alter these differences. Pulse oximetry overestimated the oxygen saturations compared to blood gas measurement across all ethnicity groups when arterial blood gas oximetry measured saturations were below 90%, and underestimated these when arterial blood gas oximetry measured saturations were above 95%.

These mean differences were particularly marked in the clinically important range when the arterial blood gas demonstrated a true oxygen saturation of 85 to 89%; individuals with a black ethnicity had a mean pulse oximetry reading that was +3.9% higher (95% CI: −8.0 to +15.9), those with an Asian ethnicity 5.8% higher (95% CI: −1.6 to −13.2) and individuals with a white ethnicity +2.4% (95% CI: −14.2 to +19.0) higher, when compared to arterial blood gas oxygenation.

 

European Respiratory Journal article – Pulse oximeters' measurements vary across ethnic groups: An observational study in patients with Covid-19 infection (Open access)

 

See more from MedicalBrief archives:

 

UK investigation into racial and gender bias in medical devices

 

GPs fail to spot two out of every three cases of pneumonia

 

CDC's health sector masking guidelines were a deadly mistake

 

 

MedicalBrief — our free weekly e-newsletter

We'd appreciate as much information as possible, however only an email address is required.