Oxygen Flow Rates and Percentages

If you wear home oxygen, you have a prescribed liter flow to give you a higher percentage of oxygen than you normally breathe. And you’ve probably heard the terms oxygen flow rate, oxygen percentage, and FiO2. While many patients use these terms interchangeably, they’re not the same things.

What is Oxygen Percentage?

Oxygen percentage is simply the percentage of oxygen in the air. Typical air consists of about 21 percent oxygen and 78 percent nitrogen, with other trace gases making up the other one percent (including neon, hydrogen, and carbon dioxide.) So, this means that typically without supplemental oxygen you’re breathing in 21 percent oxygen.

Your oxygen percentage increases when you wear supplemental oxygen, depending on how much oxygen your machine delivers. Although wearing supplemental oxygen does not change the percentage of oxygen in the air surrounding you, it changes the percentage of the oxygen you inhale. This percentage is known as FiO2.

What is FiO2?

FiO2 stands for fraction of inspired oxygen (O2). Wearing supplemental oxygen increases FiO2 from 21 percent to anywhere between 24 and 100 percent oxygen, depending on your oxygen source. Medical facilities have the capability of increasing your FiO2 to virtually 100 percent, while home units, like oxygen concentrators, deliver from 24 to 60 percent FIO2.

FiO2 and Oxygen Concentrators

Oxygen concentrators, depending on the manufacturer, produce up to 96 percent pure oxygen. (Oxygen purity of a concentrator is also known as Oxygen Concentration.) But the 96 percent oxygen produced by the unit does not mean it delivers 96 percent FiO2.

Oxygen concentrators work by pulling in room air, which is 21 percent oxygen. They then purify the air, compress the oxygen, and separate the nitrogen, delivering a higher oxygen concentration to the patient. So, although the concentrator is producing up to 96 percent oxygen, it does not mean that oxygen constitutes of 96 percent of the air you breathe. It just means that the oxygen concentrator is supplying 96% pure oxygen.

How much FiO2 you receive from your oxygen concentrator depends on your flow rate. The flow rate is how many liters of oxygen, per minute, your device delivers. For example, patients commonly use a flow rate of 2 liters per minute, but the flow rate varies by each patient's needs. A flow rate of 2 liters per minute increases the FiO2 from 21 percent (room air) to 28 percent.

Please note: The oxygen concentrator's pulse-flow setting isn't the same as continuous-flow liters per minute, and pulse dose concentrators do not measure exact liters per minute. When we refer to "flow rate," we're discussing liters per minute, not the pulse-flow setting on an oxygen concentrator.

Nasal Cannula Flow Rate and FiO2

Although certain factors, such as how fast you breathe and the size of your breaths, slightly impact the FiO2, there's a pretty good guideline to follow when determining your FiO2.

As mentioned, room air is 21 percent oxygen, so you are breathing a FiO2 of 21 percent without supplemental oxygen. When you use a flow rate of 1 liter per minute, your FiO2 increases to 24 percent. Every liter beyond that increases the FiO2 by about 4 percent.


Continuous-Flow Oxygen Liters Per Minute (LPM) to FiO2:

What FiO2 is 0 LPM of supplemental oxygen?
At room air, the approximate FiO2 is 21%. What FiO2 is 1 LPM of supplemental oxygen?
At 1 LPM, the approximate FiO2 is 24%.

What FiO2 is 2 LPM of supplemental oxygen?
At 2 LPM, the approximate FiO2 is 28%.

What FiO2 is 3 LPM of supplemental oxygen?
At 3 LPM, the approximate FiO2 is 32%.

What FiO2 is 4 LPM of supplemental oxygen?
At 4 LPM, the approximate FiO2 is 36%.

What FiO2 is 5 LPM of supplemental oxygen?
At 5 LPM, the approximate FiO2 is 40%.

What FiO2 is 6 LPM of supplemental oxygen?
At 6 LPM, the approximate FiO2 is 44%.

What FiO2 is 7 LPM of supplemental oxygen?
At 6 LPM, the approximate FiO2 is 48%.

What FiO2 is 8 LPM of supplemental oxygen?
At 6 LPM, the approximate FiO2 is 52%.

What FiO2 is 9 LPM of supplemental oxygen?
At 6 LPM, the approximate FiO2 is 56%.

What FiO2 is 10 LPM of supplemental oxygen?
At 6 LPM, the approximate FiO2 is 60%.

Understanding Oxygen Flow Rates and Percentages
The number of liters per minute generally refers to continuous flow oxygen. If you have a pulse dose concentrator, it's essential to speak with your healthcare provider to make sure you get the correct flow setting to meet your needs.

What is SpO2%?

Other than FiO2 and Oxygen purity of oxygen concentrators, SpO2% is the third measure we are talking about in this article that is measured in percentages. SpO2 is also known as blood oxygen saturation or peripheral oxygen saturation. Spo2% is a measure of percent of oxygenated hemoglobin in the blood. SpO2% can be quickly measured using over-the-counter device called finger pulse oximeter. Pulse oximeter is a small, non-invasive, and easy to use device that can show the oxygen saturation within seconds. It sends a infrared light in blood capillaries in your finger (earlobe or toes usually for infants) and measures how much light is reflected.

Healthy SpO2% is considered between 96%-99% and anything lower than 91% is considered low and requires medical attention. One should bear in mind that pulse oximeters usually have an error rate of +/-2%. That means, if the device is showing 97%, then the actual saturation could be anywhere between 95%-99%.

How Does SpO2% Help in Determining Oxygen Flow Rate?

SpO2% depicts your current blood oxygen saturation. Under normal circumstances, SpO2% of less than 91% (or less than 94% in some cases) is considered low and requires supplemental oxygen.

The oxygen liter flow required to bring back SpO2% to normal range is advised by the medical practitioner. It is not suggested to self-adjust oxygen liter flow. High supplemental oxygen can result in Oxygen Toxicity, whereas insufficient oxygen saturation can result in hypoxemia.

Final Thoughts

Use a pulse oximeter to measure your blood oxygen saturation (SpO2%). If it’s lower than normal measure of 94%, contact your medical provider. They would determine how much fraction of inspired oxygen (FiO2%) is required to maintain a health blood oxygen saturation and will prescribe Oxygen Therapy at a particular liter flow. If you are advised to administer oxygen via oxygen concentrator, then make sure that the concentrator can supply medical grade oxygen (oxygen purity over 86%) at all the flow settings.

Sources



Updated: December 1, 2021

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