Are Pulse Oximeters accurate?

Often times my patients will bring in their ‘home’ Pulse oximeters to compare with the hospital grade oximeters.  There are a number of things to understand about how a pulse ox works, in order to understand the numbers.

When you place the finger probe on your finger, the light needs to go through the nailbed. Any number if things can throw the numbers off. If the probe gets  twisted, if you have cold hands and fingers, Reynaud’s syndrome, artificial nails, fungal infections in the nail, thickened nails, sparkly or bright pink or red nail polish……… you get the idea. Also, not many pulse ox’s are made to read well with activity and movement. So you will need to stop for a sec and be still to get a reliable reading. If you are getting a reading while your hand is resting on a treadmill hand-hold, the fingers may not get full circulation and the pulse ox will not read accurately.

As a general rule, if the heart rate displayed on the pulse ox matches your heart rate, then the reading is likely accurate. Absent of the above issues, of course.

If you take a reading after being out for a walk, and the Heart Rate is only displaying a rate of 40, for example, I would not believe the 02 Sat% number.

The spectrum capacity on a pulse ox is also important, meaning, if all conditions are perfect (warm, polish-free thin nails) then the numbers above 88% are generally spot-on. However, the lower the sats below 88%, the less accurate the reading.  Someone whose sats read 79% may be in a lot bigger trouble than they think.

What do the numbers really mean?

Assuming the devices were accurate, however, there is the ‘slippery slope’ concept of sats.

At the upper end, 90% and above, the blood is almost fully saturated with oxygen. So when a patient says they were 98% when they woke up and only 94% now, It’s not a big issue. But, once you reach that 90% point, a person with lung disease can desaturate by 4% to 86% very quickly, and desaturate further very fast. Then, it takes a long time to recover.

Always keep your sats above 90% to protect your heart. There are some people who are unable to saturate up to 90%. Your doctor can tell you if this is true for you.