In laimans terms, it is the amount of Oxygen the patients blood is carrying at that moment.
Tecnically and but very quickly so that you are not bored to death, Oxygen Saturation, SaO2 or SpO2, is the percentage of haemoglobin carrying oxygen versus the total amount of haemoglobin in our blood. SaO2 is measured directly by using an arterial blood sample, and SpO2 is measured using Pulse Oxymetry. We’ll talk more about this in a minute.
Lets understand a bit how our bodies work!
Understanding Oxygen Saturation
First, think Oxygen, specifically about the Oxygen molecule O2. Oxygen is the most important molecule for our bodies and its cells. It is used by every single organ of our bodies to produce energy, and therefore keep us alive. Left without oxygen we humans begin to die in just 4 to 5 minutes. It is that important!
Oxygen enters our body when we bread air, and it goes to our lungs. In our lungs it gets transferred into our blood (in a process called…. ). Our blood is then pumped by our heart to every single organ of our bodies. There it will release O2 to the organs, allowing them to produce energy, and collect Carbon Dioxide.
What makes our blood able to carry oxygen are the Red Blood Cells that exist in our blood, and in particular a protein that exists inside the Red Blood Cells, called Hemoglobin.
Side note: Hemoglobin is also what give the red color to a Red Blood Cell, and this is also the reason blood it red
During the technical description it was said “percentage of hemoglobin carrying oxygen versus the total amount of hemoglobin” , this is what was meant: If a lot of Hemoglobin in our blood is carrying oxygen, then we have a High percentage of Oxygen Saturation. If on the other hand, a lot of the Hemoglobin is not carrying oxygen, we have a Low percentage of Oxygen Saturation.
What is a normal SpO2 level?
The oxygen saturation levels should be at least 90%. A measurement between 95% and 100% is the considered normal reading. Measurements below 90% are considered abnormally low (Hypoxemia) and a possible sign that something is not right.
Hypoxemia and Hypoxia
Low levels of oxygen in the blood is called Hypoxemia, which is what happens when SpO2 measurements are below 90%.
Because the blood is carrying too little oxygen to the organs and cells of our bodies, certain regions of bodies can become deprived of oxygen, which is called Hypoxia.
Usually, the first regions to become Hypoxic are the extremities of the body, simply because the blood reaching those areas is already lacking oxygen, having released it to other organs and cells before reaching those extremities.
Causes for low SpO2
There are several factors that could contribute to a low SpO2 reading.
First and foremost, oxygen entering our bodies comes from the air we breathe, therefore the air must contains enough oxygen. So altitude or situations that cause oxygen deprivation should be taken into account while performing an SpO2 reading.
The oxygen in the air must be transferred to our blood stream, so any problem at the respiratory level could lead to a lower SpO2 reading.
Any Chronic Obstructive Pulmonary Disease (COPD) or Interstitial Lung Diseases can cause lower levels of oxygen saturation:
- Emphysema : where the alveoli in our lungs are damaged and don’t perform the transference of oxygen to the blood as well as they should.
- Chronic Bronchitis : where the interior of the lungs is irritated and inflamed to the point of thickening the tissues of the lungs, causing difficulty in breathe.
- Pulmonary fibrosis : scarring of the lungs, which lead to problems to breathe
- Sarcoidosis : where abnormal masses (granulomas) form around the lungs conditioning the ability to breathe.
Other conditions, such as Asthma, can also lead to abnormally low SpO2 readings. With Asthma, the airways swell and get narrower making it very hard to breathe. Also the swelling leads to the production of mucus which also makes it harder to breathe.
Also other situations arising from trauma, such as a collapsed lung, and lung perforation can lead to Hypoxemia.
Blood related conditions
Because the oxygen is taken to all the organs and cells of our bodies through our blood, this can also be a factor for a low oxygen saturation reading.
Red Blood Cell counts
The cells on our blood that carry the oxygen are the Red Blood Cells, so it is of critical importance that there are a correct number of those. Both low and high counts of Red Blood Cells can lead to bad oxygen saturation reading and problems.
With a high Red Blood Cell count, there is more blood, and it is hard to deliver oxygen to all that amount of blood, leading to a low oxygen saturation due to the sheer volume of blood.
With a low Red Blood Cell count, it is much easier to saturate the blood with oxygen, which will lead to a high SpO2 reading. In these cases the SpO2 is a bad indicator because saturation will be high but oxygen content is low, because there are very few blood cells carrying it.
A low Red blood Cell count is called Anemia.
Some low Red Blood Cell count conditions can be:
- Aplastic Anemia : when the body is not producing enough Red Blood Cells.
- Urinary Tract Infection : which can destroy existing Red Blood Cells.
Hemoglobin is a protein that exists inside the Red Blood Cells and it is responsible for carrying oxygen. It is also responsible for carrying the Carbon Dioxide from the organs and cells back to the lungs for being expelled.
Because the only way a Red Blood Cell can carry oxygen to the organs and cells is through the existence of hemoglobin inside, the existence of enough hemoglobin and the lack of problems with said hemoglobin is a big factor on the oxygen saturation equation.
Some Hemoglobin Related conditions are:
- Iron Deficiency Anemia is when there is a low count of Hemoglobin, but the Red Blood Count can still be high. This happens when there is a deficiency of Iron in our bodies, which is a core component for creating Hemoglobin. In these situations, the Red Blood Cells will have low Hemoglobin, therefore carrying less oxigen.
- Pernicious Anemia is a disease where the body is lacking the GIF protein (Gastric Intrinsic Factor) that is used to absorb B12 vitamin in the small intestine. B12 is also a core component for creating Hemoglobin.
But lower Hemoglobin counts are also not always a sign of trouble. Pregnant woman can have low hemoglobin counts, so this is also a factor to have in mind.
Heart and Circulatory Conditions
For the blood to reach all the organs and cells of our bodies to release the oxygen which the Red Blood Cells are carrying through the use of Hemoglobin, it needs to be pumped and it needs to be able to reach those organs.
Problems with the Heart and circulatory system can lead to poor circulation of the blood and can lower the amount of oxygenated blood being delivered to all the organs and cells of our bodies. In these cases it will cause a lower oxygen saturation reading.
If fact, oxygen saturation reading are commonly used to help diagnose Critical Congenital Heart Defects.