Pulse oximeters give biased results for people with darker skin • Hacker News Board

Re: Pulse oximeters give biased results for people with darker skin

#91

Post by PascLeRasc » Thu, Aug 06, 2020, 5:32 PM UTC

adrianmonk wrote: post #89

PascLeRasc wrote: post #21

I'm a student EMT and our instructor told us not to rely on a pulse ox reading if our patient has dark skin, or if they were in a fire, or are a lifelong smoker, or if they have any nail polish or dirt/grease on their fingertips. We just look for the 94-100% range and would only take action if we get a reading around 87% or lower, or see a sudden drop during treatment. There are a few alternatives designs that aim to…

> We just look for the 94-100% range and would only take action if we get a reading around 87% or lower I'm not very familiar, so I'm not sure how to interpret this. Does this describe the normal procedure for when you can rely on a pulse oximeter, or does it describe the modified procedure for when you can't?

That's the normal procedure, as far as I know. Taking a pulse ox reading is done at the same time as we'd get blood pressure, listen to breath sounds and watch chest expansion depth/rate, and talk to the patient about how they're feeling or what's wrong. It's just one factor that could tell us that they're short of breath and we should provide oxygen, but it's important to consider the patient as a whole. They like to say "treat the patient, not the data".

Re: Pulse oximeters give biased results for people with darker skin

#92

Post by CositaS » Thu, Aug 06, 2020, 5:33 PM UTC

zamfi wrote: post #71

treis wrote: post #13

This really isn't a big deal. Doctors know that these pulse ox meters aren't very accurate and use them accordingly. Nobody's changing their plan because you have a pulse ox of 93 instead of 95. They're there to quickly measure big changes that indicate a problem. In other words, they're looking for patients going from 98 to 75, not 98 to 95.

Frustratingly, this kind of dismissal perpetuates injustices. First, let's be clear: > Doctors know that these pulse ox meters aren't very accurate and use them accordingly Some doctors know... > Nobody's changing their plan because you have a pulse ox of 93 instead of 95. They're there to quickly measure big changes that indicate a problem. Sometimes , perhaps even often , they're used for this. It's one use case of…

Also, while they might not change plan because of a reading of 93 instead of 95 - the article describes a bias of up to 8%, which does seem enough to be significant.

Re: Pulse oximeters give biased results for people with darker skin

#93

Post by slowmovintarget » Thu, Aug 06, 2020, 5:41 PM UTC

zamfi wrote: post #71

treis wrote: post #13

This really isn't a big deal. Doctors know that these pulse ox meters aren't very accurate and use them accordingly. Nobody's changing their plan because you have a pulse ox of 93 instead of 95. They're there to quickly measure big changes that indicate a problem. In other words, they're looking for patients going from 98 to 75, not 98 to 95.

Frustratingly, this kind of dismissal perpetuates injustices. First, let's be clear: > Doctors know that these pulse ox meters aren't very accurate and use them accordingly Some doctors know... > Nobody's changing their plan because you have a pulse ox of 93 instead of 95. They're there to quickly measure big changes that indicate a problem. Sometimes , perhaps even often , they're used for this. It's one use case of…

This IS NOT BIAS! This is physics!

As someone else pointed out, this isn't only about melanin in the skin. Darkened skin for any reason will cause this (burns, smoking, dirt, etc...). Medical personnel are trained to account for this partial accuracy.

The other fact is that there are newer techniques being worked on to improve the technology.

Re: Pulse oximeters give biased results for people with darker skin

#94

Post by khuey » Thu, Aug 06, 2020, 5:41 PM UTC

wombatmobile wrote: post #87

GUIDELINES FOR SPO2 MEASUREMENT USING THE MAXIM® MAX32664 SENSOR HUB The SpO2 measurement performance of a device must be verified before the device is released to the market. The U.S. Food and Drug Administration (FDA) suggests using standards presented in the following: ISO 80601-2-61:2017 – Medical electrical equipment -- Part 2-61: Particular requirements for basic safety and essential performance of pulse oximet…

Seems like it would be better if instead of merely an overall error of at most 3% they required an error of at most 3% in the subpopulations of interest too.

Re: Pulse oximeters give biased results for people with darker skin

#95

Post by adrianmonk » Thu, Aug 06, 2020, 5:43 PM UTC

PascLeRasc wrote: post #91

adrianmonk wrote: post #89

Earlier quoted context omitted.

> We just look for the 94-100% range and would only take action if we get a reading around 87% or lower I'm not very familiar, so I'm not sure how to interpret this. Does this describe the normal procedure for when you can rely on a pulse oximeter, or does it describe the modified procedure for when you can't?

That's the normal procedure, as far as I know. Taking a pulse ox reading is done at the same time as we'd get blood pressure, listen to breath sounds and watch chest expansion depth/rate, and talk to the patient about how they're feeling or what's wrong. It's just one factor that could tell us that they're short of breath and we should provide oxygen, but it's important to consider the patient as a whole. They like t…

Thanks. So in a case where you cannot rely on it, do you completely avoid using the pulse oximeter at all? Or do you use it but place less faith in the readings and interpret the readings differently?

Re: Pulse oximeters give biased results for people with darker skin

#96

Post by throwanem » Thu, Aug 06, 2020, 5:50 PM UTC

slowmovintarget wrote: post #93

zamfi wrote: post #71

Earlier quoted context omitted.

Frustratingly, this kind of dismissal perpetuates injustices. First, let's be clear: > Doctors know that these pulse ox meters aren't very accurate and use them accordingly Some doctors know... > Nobody's changing their plan because you have a pulse ox of 93 instead of 95. They're there to quickly measure big changes that indicate a problem. Sometimes , perhaps even often , they're used for this. It's one use case of…

This IS NOT BIAS ! This is physics! As someone else pointed out, this isn't only about melanin in the skin. Darkened skin for any reason will cause this (burns, smoking, dirt, etc...). Medical personnel are trained to account for this partial accuracy. The other fact is that there are newer techniques being worked on to improve the technology.

> This IS NOT BIAS! This is physics!

Bias doesn't happen in physics. Bias happens where humans and physics interact.

> Medical personnel are trained to account for this

Medical personnel aren't the only people who use pulse oximeters and need them to read reliably. Beyond that, this thread and the article it discusses are full of examples of why "medical personnel are trained" isn't enough of an answer here.

Re: Pulse oximeters give biased results for people with darker skin

#97

Post by Teknoman117 » Thu, Aug 06, 2020, 5:53 PM UTC

zamfi wrote: post #71

treis wrote: post #13

This really isn't a big deal. Doctors know that these pulse ox meters aren't very accurate and use them accordingly. Nobody's changing their plan because you have a pulse ox of 93 instead of 95. They're there to quickly measure big changes that indicate a problem. In other words, they're looking for patients going from 98 to 75, not 98 to 95.

Frustratingly, this kind of dismissal perpetuates injustices. First, let's be clear: > Doctors know that these pulse ox meters aren't very accurate and use them accordingly Some doctors know... > Nobody's changing their plan because you have a pulse ox of 93 instead of 95. They're there to quickly measure big changes that indicate a problem. Sometimes , perhaps even often , they're used for this. It's one use case of…

I'd hardly call it injustice. Anything based on light is going to be variable depending on skin tone (or, as other have mentioned, darkened skin for any reason).

The only thing you could claim injustice for would be if there was no other mechanism for measuring blood oxygen other than something that was known to not work properly for people of color.

Re: Pulse oximeters give biased results for people with darker skin

#98

Post by treis » Thu, Aug 06, 2020, 5:57 PM UTC

Edmond wrote: post #25

PascLeRasc wrote: post #21

I'm a student EMT and our instructor told us not to rely on a pulse ox reading if our patient has dark skin, or if they were in a fire, or are a lifelong smoker, or if they have any nail polish or dirt/grease on their fingertips. We just look for the 94-100% range and would only take action if we get a reading around 87% or lower, or see a sudden drop during treatment. There are a few alternatives designs that aim to…

The article notes that the devices inaccurately report higher oxygen levels for darker skin tones. Meaning if someone dark skinned reports a result that falls into the 94-100% range, they may in fact be at lower oxygen levels that put them at risk.

The bias is smaller than the actual measurement error. The measurement error is around +/- 1. So a 96 reading means actual blood O2 of 95-97. The bias introduced by skin color is around 0.5. So a 96 reading means 95-97 in a white person and 94.5-96.5 in a black person. The bias from skin color isn't significant because the measurement itself is pretty inaccurate.

Re: Pulse oximeters give biased results for people with darker skin

#99

Post by sangnoir » Thu, Aug 06, 2020, 6:00 PM UTC

treis wrote: post #13

This really isn't a big deal. Doctors know that these pulse ox meters aren't very accurate and use them accordingly. Nobody's changing their plan because you have a pulse ox of 93 instead of 95. They're there to quickly measure big changes that indicate a problem. In other words, they're looking for patients going from 98 to 75, not 98 to 95.

> In other words, they're looking for patients going from 98 to 75, not 98 to 95

The problem is that that '95' might really be a '90' - surely a drop from 98 to 90 is a cause for concern. If that information is being hidden, it needs to be fixed, regardless of other, more subjective fallback methods.

Re: Pulse oximeters give biased results for people with darker skin

#100

Post by klyrs » Thu, Aug 06, 2020, 6:02 PM UTC

slowmovintarget wrote: post #93

zamfi wrote: post #71

Earlier quoted context omitted.

Frustratingly, this kind of dismissal perpetuates injustices. First, let's be clear: > Doctors know that these pulse ox meters aren't very accurate and use them accordingly Some doctors know... > Nobody's changing their plan because you have a pulse ox of 93 instead of 95. They're there to quickly measure big changes that indicate a problem. Sometimes , perhaps even often , they're used for this. It's one use case of…

This IS NOT BIAS ! This is physics! As someone else pointed out, this isn't only about melanin in the skin. Darkened skin for any reason will cause this (burns, smoking, dirt, etc...). Medical personnel are trained to account for this partial accuracy. The other fact is that there are newer techniques being worked on to improve the technology.

> This IS NOT BIAS! This is physics!

You sound pretty emotional, maybe tone it down and try to think objectively.

Just because there's an underlying physical reason for the device to be inaccurate on a subset of the population, doesn't mean that it's fair to use that device on the impacted population. It's been accepted by the medical community, despite the additional training required to correctly use the device -- amounting to guesswork when the medical personnel remember that it's necessary. Accounting for human error, this means that affected populations will receive a lower quality of care.

Just a hypothetical. Would it be accepted if it was accurate for black women, and required guesswork when treating white men? Because there is a long history of significant bias in medical studies. Just because "it's just physics" explains the device's flaw, doesn't mean that acceptance of a flawed device isn't a result of systemic bias.