Running On Air, a nonprofit I started, is working to educate patients and medical professionals about portable oxygen concentrators (POCs) and the limitations on how much oxygen they deliver to patients. Most people do not know how much (or little) they give, and many are shocked when they find out.

When I started supplemental oxygen ten years ago, I did not want to be saddled with tanks. My prescription was for 2 lpm for exertion, which for me at that time was working out at the gym. I also needed it when flying. I’d seen portable oxygen concentrators, but I didn’t know anything about them. It took me 8 months to finally find an FAA approved one I could rent.

I kept getting a lot of mixed information on how much oxygen I was actually getting through the device. The chart in the manual had numbers in milliliters, yet my prescription was in liters. Even on the highest setting, the amount shown on the chart was not close to my prescription.

There is so much contradictory information from healthcare professionals and from POC sellers that I did not know what was correct. I found the Pulmonary Paper, which had an annual guide to POCs. It helped, but I still found it all confusing.

One point from the “Pulmonary Paper” that has stuck with me is that POCs can be lightweight, give high concentrations of oxygen at all settings, and deliver higher flow, but it cannot be all three. To be FDA approved requires a high concentration of oxygen at all settings, so POCs are either lightweight and lower flow or heavier and higher flow (not to be confused with “high flow,” which refers to 4 liters or higher).

Part of the confusion is POC settings are numerical. Many people think the settings are the same as continuous flow liters per minute (lpm), but that’s not the case. Unfortunately, this idea is reinforced with device advertising that says a 5 setting POC gives “up to” 5 lpm. It’s not a big mental leap then to think setting 5 must be the equivalent to 5 lpm.

Most pulse only POCs use minute volume dosing. What this means is over the course of a minute, the specified setting will deliver a set amount. Let’s say setting 5 gives 1 liter over a minute. The amount given for each breath then will depend on the breath rate. The slower a person is breathing, the more oxygen in each bolus. The faster they breathe, the less oxygen in each bolus. This is because the bolus is the setting minute volume, in this case, 1 liter, divided by the number of breaths. 20 breaths per minute (bpm) yields 50 ml per breath, whereas 40 bpm gives 25 ml per breath.

The confusing part is how to equate this to continuous flow, on which prescriptions are based. Here’s an extremely simplified way of thinking about it:

Say a person’s prescription is for 3 lpm (makes the math easier). The person isn’t breathing in all 3 liters over the course of a minute on continuous flow.  This example assumes the person’s inhalation is exactly 1 second. If the breath rate is 15 bpm, that’s a quarter of a minute. A quarter of 3 liters is 0.75 liters. This means that a POC setting that provides 0.75 liters over a minute will likely meet the 3 lpm continuous flow need at 15 bpm.

Now, let’s say the breath rate goes to 20 bpm, which is still considered a resting breath rate. That’s a third of a minute. A third of 3 liters is 1 liter. A POC that provides 1.0 liter over a minute should meet the person’s prescription at this breath rate.

However, when we jump up to 30 bpm, which is half a minute, we need a POC that provides 1.5 liters in a minute. There is currently no pulse-only(on-demand) POC that will do this. The highest a pulse-only POC currently goes is 1.4 liters over a minute.

From this example, you can see that pulse-only POCs can’t provide the amount prescribed above a resting breath rate for 3-liter prescriptions.

 This is not to say that someone with a 3-liter prescription should not use a pulse-only POC. They should be evaluated on it though to ensure that it meets their needs with their usual activity level and that they have a strong enough inhalation to trigger the pulse.

There are also several things that can affect the performance of a POC. POCs have a variability of +/-15%. The maximum breath rate most can handle is 40 bpm. Cold or hot temperatures can affect the POCs’ performance. Altitudes over 8,000 – 10,000 may affect the oxygen concentration.

If understanding FDA-approved POCs isn’t challenging enough, we also must contend with “non-concentrators,” or non-FDA approved devices on online markets advertising themselves as having high liter flow and costing under a thousand dollars. The problem is these devices do not have a higher oxygen concentration as the flow levels increase. You can learn more from a study conducted in 2023 here:  https://pubmed.ncbi.nlm.nih.gov/36400446/

To help mitigate some of this confusion, Running On Air started producing a brochure called “Portable Oxygen Guide with Comparison Chart” in May 2023, which is meant for patients and healthcare providers. We update our website periodically as new POCs come on the market or old ones are retired. We update the brochure a few times during the year as needed. Our website has more information on POCs, including charts on settings and battery life.

We feel it is important for patients to have this information, especially before investing thousands of dollars in buying a POC outright. To help them get this brochure, we will ship ten or more brochures for free to medical facilities. They can be ordered at https://runningonair.net/orders

Mary Kitlowski

President and Founder of Running On Air

Supplemental oxygen user

Patient Advocate

Reference

The Pulmonary Paper https://www.pulmonarypaper.org/portable-oxygen-concentrators-comparison-chart-2019/