Oxygen saturation (medicine)

Oxygen saturation is a very important measure that tells us how much oxygen is in our blood. It shows the amount of oxygen that is attached to a special material in our blood called hemoglobin. Our bodies need just the right amount of oxygen to work well.

Usually, a healthy person's blood has between 96 to 100 percent oxygen. If the level drops below 90 percent, it is called hypoxemia and can be dangerous. If it goes even lower, below 80 percent, it can hurt important parts of the body like the brain and heart. Doctors may use oxygen therapy to help raise low oxygen levels.

Oxygen gets into our blood in our lungs, where air we breathe passes into the blood. This process is called oxygenation, and it is key to keeping our bodies healthy.

Definition

In medicine, oxygen saturation measures how much oxygen is attached to hemoglobin in our blood. It tells us what percentage of the hemoglobin sites are holding oxygen. When there is not much oxygen around, most of the hemoglobin does not have oxygen attached to it. But as oxygen levels go up, more and more hemoglobin gets filled with oxygen, reaching close to 100% when there is plenty of oxygen. A pulse oximeter is a small device that can show us this level by using light to check how much oxygen is in the blood.

Physiology

The body keeps a steady level of oxygen in the blood through natural processes linked to breathing. Our respiratory system helps red blood cells, which contain a special material called hemoglobin, pick up oxygen in the lungs and carry it to all parts of the body. Sometimes, the body needs more or less oxygen, like when we exercise or when we are high up in the mountains. A blood cell is "saturated" when it has just the right amount of oxygen. Having too much or too little oxygen can be bad for our health.

Measurement

When the level of oxygen in your blood, called SaO₂, drops below 90%, it can mean you have hypoxemia. Hypoxemia is when your body doesn’t get enough oxygen. Low oxygen levels can sometimes make your skin look bluish, which is called cyanosis. Doctors can check oxygen levels in different parts of the body to make sure everything is working well.

Main article: hypoxemia

Pulse oximetry

Main article: Pulse oximetry

Pulse oximetry is a way to check how much oxygen is in your blood. A small device, called a pulse oximeter, clips onto a part of the body like a finger or an earlobe. It uses tiny lights and a sensor to measure how much oxygen is bound to special molecules in the blood, giving a reading called SpO₂. This helps doctors know if you have enough oxygen.

Medical significance

Most healthy people at sea level have oxygen levels in their blood between 96% and 99%, and they should be above 94%. When you go higher up, like about one mile above sea level, oxygen levels should still be above 92%.

If the oxygen level in the blood drops below 90%, it can cause low oxygen in the body, called hypoxia. This low oxygen might make the skin look bluish, known as cyanosis. However, the oxygen level in the blood doesn’t always show how well oxygen is reaching the body’s tissues. Several factors can change how easily oxygen is released to the tissues, like changes in blood acidity, body temperature, and certain chemicals in the blood.