Back then, in the ER, they’d put a nasal cannula on me—little prongs in the nose, oxygen flowing. The problem was, I didn’t feel fine—I was having trouble breathing—but that thing on my face made me feel restricted.
So as soon as they left the room, I’d take it off. They’d come back in, put it back on. They’d leave, I’d take it off again. We went back and forth like that more than once until they finally gave up. And I would always be admitted -- if I was admitted -- on room air.
At one point, someone decided, “If you won’t wear the cannula, we’ll try an oxygen tent.” So they did.
That lasted about an hour.
I didn’t like that either.
So there I was—being put on oxygen, clearly supposed to need it—and I didn’t want it. Which raises a fair question:
How did they even know I needed oxygen?
The honest answer is—they mostly didn’t.
Not the way we do today.
Back then, you were looking for signs. Blue lips. Blue fingertips. Work of breathing. How you looked. How you sounded. If you wanted a real number, you had to draw blood—an arterial blood gas (which they did a few times). Accurate, but not something you were doing every few minutes.
And then, everything changed.
When My Finger Told the Story
I didn’t see it until 1991.
Another asthma attack. Another ER visit. And this time, they clipped something onto my finger.
No needles. No blood. Just a clip.
I stared at it and started asking questions.
“What is that?”
They told me it was measuring my oxygen.
That didn’t make sense to me. Up until that point, oxygen was something you guessed at, or something you pulled out of an artery with a syringe. Now this little device was just… reading it?
It felt like science fiction.
But it wasn’t.
Pulse oximetry had been around in development for years, but it really took off in the 1980s when the technology finally caught up. Suddenly, you could monitor oxygen continuously, noninvasively, in real time.
No needles. No waiting. Just a number.
At first, the machines were big. Expensive. Not something every room had. But as the technology improved, they got smaller, cheaper, and more reliable. By the 1990s, they were becoming standard. By the 2000s, they were everywhere.
Now?
You can grab one for $25 at Walmart, a pharmacy, or Amazon. Toss it in a drawer like a thermometer.
That would’ve blown my mind back in that ER room—when I was taking off my oxygen and they were trying to decide if I actually needed it.
Because today, there’s no guessing.
You put the clip on the finger…
…and the finger tells the story.
So What Is It Actually Doing?
Here’s the simple version.
A pulse oximeter measures how much oxygen your blood is carrying. Not the oxygen in the air. Not your breathing rate. Your blood.
And it does it with light.
Inside that little clip are two lights:
- one red
- one infrared
They shine through your finger. On the other side, there’s a sensor catching that light.
Now here’s the trick:
Oxygenated blood and deoxygenated blood absorb light differently. One soaks up more red light, the other more infrared. The device compares the two and uses that difference to estimate your oxygen saturation—your SpO₂.
It also times it with your pulse, so it knows it’s reading fresh arterial blood, not just everything sitting in your finger.
No blood draw. No guesswork. Just physics.
From Bulky Boxes to Your Fingertip
The early machines weren’t sleek.
They were big. Expensive. Wires everywhere. You didn’t carry one around—you rolled it.
Then they got smaller. Handheld units. Clip-on probes.
And now, the whole thing is the clip.
You slide it on your finger, wait a few seconds, and there it is:
- your oxygen level
- your pulse
Something that used to require a needle and a lab can now be done in your living room while you’re watching TV.
You put the clip on the finger…
and the finger tells the story.
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