"Your blood oxygen level is a measure of how much oxygen your red blood cells are carrying. Your body closely regulates your blood oxygen level. Maintaining the precise balance of oxygen-saturated blood is vital to your health.
Most children and adults don’t need to monitor their blood oxygen level. In fact, many doctors won’t check it unless you’re showing signs of a problem, like shortness of breath or chest pain."
https://www.healthline.com/health/normal-blood-oxygen-level#basics
"Blood oxygen level is the amount of oxygen circulating in the blood. Doctors consider oxygen levels to be low when they are below 60 millimeters of mercury (mm Hg). Shortness of breath, dizziness, and other symptoms may occur.
Blood oxygen level usually range from 75–100 mm Hg. If they fall below 60 mm HgTrusted Source, there may not be enough oxygen reaching the body’s vital organs. This can lead to a range of symptoms.
The body closely monitors blood oxygen levels to keep them within a specific range so that there is enough oxygen for the needs of every cell.
A person’s blood oxygen level indicates how well the body distributes oxygen from the lungs to the cells, and it can be important for people’s health."
https://www.medicalnewstoday.com/articles/321044
"Your blood oxygen level (blood oxygen saturation) is the amount of oxygen you have circulating in your blood.
Oxygen is essential to life, and our bodies need a certain amount of oxygen to function properly. Oxygen enters your body through your nose or mouth when you breathe (inhale) and passes through your lungs into your bloodstream. Once in your bloodstream, the oxygen then goes to cells all over your body. All of your cells need oxygen to create energy efficiently, and your body needs energy to fulfill all of its processes, such as digestion and even thinking.
Once your cells use oxygen, they create carbon dioxide. Your bloodstream then carries the carbon dioxide back to your lungs, and you breathe it out (exhale it) through your mouth or nose.
Your body tightly regulates the amount of oxygen saturation in your blood, because low blood oxygen levels (hypoxemia) can lead to many serious conditions and damage to individual organ systems, especially your brain and heart. Low blood oxygen levels indicate that your lungs and/or circulatory system may not be working as they should."
https://my.clevelandclinic.org/health/diagnostics/22447-blood-oxygen-level
"Your blood oxygen level helps you know how well your lungs, heart, and circulatory system work. A typical blood oxygen level for a healthy person ranges between 95% and 100%. This means that nearly all of the red blood cells are carrying oxygen to your cells and tissues."
https://www.webmd.com/fitness-exercise/how-to-increase-blood-oxygen-level