Oxygen saturation (medicine)

Oxygen saturation (medicine)

Oxygen saturation is a measure that shows how much oxygen is in our blood. It tells us how much oxygen is connected to a special material in our blood called hemoglobin. Our bodies need the right amount of oxygen to stay healthy.

For most healthy people, the oxygen in their blood is between 96 to 100 percent. If the level drops below 90 percent, it is called hypoxemia and can be unsafe.

Oxygen enters our blood in our lungs when we breathe. This process is called oxygenation, and it helps keep our bodies working well.

Definition

In medicine, oxygen saturation measures how much oxygen is attached to hemoglobin in our blood. It tells us the percentage of hemoglobin that is carrying oxygen. When there is little oxygen around, most of the hemoglobin does not have oxygen. But when there is more oxygen, more hemoglobin gets filled, reaching almost 100% when there is plenty of oxygen. A pulse oximeter is a small device that shows this level by using light to check the oxygen 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 affect our health.

Measurement

When the amount of oxygen in your blood, called SaO₂, drops below 90%, it may mean you have hypoxemia. Hypoxemia means your body is not getting enough oxygen. Low oxygen levels can sometimes make your skin look bluish. This bluish color 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 the oxygen in your blood. A small device, called a pulse oximeter, clips onto a finger or earlobe. It uses tiny lights and a sensor to measure the oxygen, giving a reading called SpO₂. This helps doctors see if you have enough oxygen.

Medical significance

Most healthy people at sea level have oxygen levels in their blood between 96% and 99%. 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. This low oxygen might make the skin look bluish, known as cyanosis. The oxygen level in the blood doesn’t always show how well oxygen is reaching the body’s tissues. Several factors can change this, like changes in blood acidity, body temperature, and certain chemicals in the blood.