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False pulse oximeter readings in black patients

A new study published in the New England Journal of Medicine says pulse oximeter results are three times likely to give misleading results in patients…

A new study published in the New England Journal of Medicine says pulse oximeter results are three times likely to give misleading results in patients with black skin.

A pulse oximeter is a small device attached to the thumb which tells healthcare workers a person’s level of blood oxygenation.

A pulse oximeter works by a process that senses the level of oxygen in the blood by passing light through the skin. It’s thought that the wrong result in black skin could be because darker skin pigments absorb light differently.

Since the COVID-19 pandemic, there has been an increase in the use of the device. It helps to know the patients who are in critical conditions and who might benefit from the use of oxygen, or to make a decision to transfer a patient to the intensive care units. Those who are isolating at home can also use it to monitor their own condition too, to know if they need to go to hospital urgently.

Interestingly, this is not the first time this has been reported. Some years ago, a research brought this issue up, but it was not taken seriously. But this latest research in a pandemic changes everything.

Some also say the report underscores a racial discrimination in the practice of medicine, especially for a pandemic that has killed more Blacks and Hispanics in America than white people.

Dr. Michael W. Sjoding, an assistant professor of internal medicine at the University of Michigan Medical School and lead author of the new report, said, “I think most of the medical community has been operating on the assumption that pulse oximetry is quite accurate.” He added, “I’m a trained pulmonologist and critical care physician, and I had no understanding that the pulse ox was potentially inaccurate — and that I was missing hypoxemia in a certain minority of patients.”

The research analysed pulse oximeter results and compared them with results from arterial gas measurements which is a more invasive test. Arterial blood gas requires blood to be drawn and this test is rarely done these days.

The results of 10,789 paired tests from 1,333 white patients and 276 black patients hospitalised at the University of Michigan showed that pulse oximetry “overestimated oxygen levels 3.6 percent of the time in white patients, but got it wrong nearly 12 percent of the time, or more than three times more often, in black patients.”

The pulse oximeter wrongly gave oxygen levels for these patients between 92 and 96 percent, when it was indeed as low as 88 percent. Oxygen levels less than 95 are said to be abnormal.

The researchers also analysed a multi-hospital database comparing 37,308 paired tests from ICU patients hospitalised at 178 medical centres in 2014 and 2015, and found same discrepancies.

There are suggestions that the pulse ox could be improved with a setting that adjusts for a different calibration for a darker pigmented skin. It’s also suggested that the device carries a warning label that lets users be aware of  potential for the device to overestimate oxygen levels in black patients.

While we hope that local studies can be done to see whether the same results are also seen in Nigeria, it’s a wake-up call to healthcare workers in Nigeria to see patients holistically and individually, and not to rely too much on a device that in itself can malfunction.

Dr Cosmas Odoemena, medical practitioner, Lagos

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