Oxygen saturation measures how much hemoglobin is currently bound to oxygen compared to how much hemoglobin remains unbound. When your body repeatedly stops breathing due to obstructive sleep apnea, it inhibits the body's ability to produce oxygen. It typically becomes concerning if oxygen levels in the body fall below 90%. To put this in a little bit more context, hospitals will typically put oxygen masks on their patients when oxygen levels drop below 92%. It is not uncommon to see people with OSA drop into the 80's, 70's, 60's, and even 50's range, which shows just how severe obstructive sleep apnea can be.

The reason that low oxygen saturation is so dangerous is because it can lead to irreversible brain damage, heart attack, or stroke.