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Researchers have raised concerns about the reliability of pulse oximetry in the assessment of patients with COVID-19 infection, particularly those from Black, Asian, and minority ethnic groups, warning that this could lead to a delay in patients receiving appropriate care.
The University of Nottingham and Nottingham University Hospitals NHS Trust study, published in the European Respiratory Journal, found that pulse oximeters gave falsely high readings in all groups when compared with arterial blood readings, with oximetry readings being 6.9% higher in those of mixed ethnicity compared with 3.2% higher in White patients.
The authors pointed out that the light wave transmission that pulse oximetry uses is modified by skin pigmentation and thus may vary by skin colour. The researchers highlighted that a previous study of paired measures of oxygen saturation from pulse oximetry and arterial blood gas reported differing outputs in patients with Black skin compared with patients with White skin, and that this had the potential to impact adversely on patient care. This led to the Food and Drink Administration in the US releasing an expression of concern about the accuracy of pulse oximeters in 2021.
Darker Skin Affects Accuracy of Pulse Oximetry Readings
For their study the researchers used routinely collected electronic data for 2997 eligible patients admitted with either suspected or confirmed SARS-CoV-2 to Nottingham University Hospitals NHS trust between February 1, 2020 and September 5, 2021. Using data comprising 5374 paired oxygen saturations, they explored the difference of blood oxygen levels as measured by pulse oximetry and arterial blood gases, with paired samples taken within a 30 minute time window. The authors said that data from intensive care units were not available.
They found that the mean difference between oxygen saturations as measured by pulse oximetry compared with arterial blood gas was highest in the mixed ethnic group (+6.9%; 95% CI: −21.9 to +35.8), followed by those in the Black group (+5.4; 95% CI: −25.9 to +36.8), then those in the Asian group (+5.1%; 95% CI: −23.8 to 34.0), with the lowest difference being in the White group (+3.2%; 95% CI: −22.8 to +29.1).
“A sensitivity analysis restricting to a 10-minute window did not alter these differences,” said the authors.
In their study, the authors commented that the mean differences were particularly marked in the clinically important range when the arterial blood gas demonstrated a true oxygen saturation of 85-89%. Their results showed that 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 with arterial blood gas oxygenation.
May Delay Timely Medical Care
In December 2021, through the access given to GPs to up to 250,000 pulse oximeters, COVID-19 positive patients would be able to monitor their own blood oxygen levels at home, with the aim of helping to ensure that only those who need to be would be admitted to hospital.
Dr Andrew Fogarty, from the School of Medicine at Nottingham University and the lead author of the study, said: “This data builds on what we know, which is that patients with darker skin have less accurate oxygen measurements using the pulse oximeters.”
The new research is particularly relevant, the authors said, as “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”.
Dr Fogarty added: “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.”
Delays in appreciating the severity of COVID-19 pneumonitis is likely to be detrimental to patient care, especially now that new therapeutic options are becoming available, the authors said.
The study authors concluded by saying that their research “extends the concerns about pulse oximeters giving a falsely high reading in patients with Black ethnicity to those from Asia as well”.
They highlighted how important this is, since high levels of skin pigmentation are associated with the ethnic groups which have a poorer outcome from COVID-19 infection, and therefore need the most accurate oxygen measurements in order to guide appropriate and timely treatment.
Dr Fogarty said that he and his team will now explore the impact of this on clinical outcomes to see if it may have led to “any issues in escalating treatment intensity” for their patients.
Créditos: Comité científico Covid