Settings are NOT Liters

One of the most important things to know about POCs is that the settings, or levels, for pulse modes are not the same as liters.  This is something that is misunderstood by many doctors, respiratory therapists and patients.  Some POCs are advertised based on their settings and how you can more closely tailor the level of oxygen to your needs.  More settings are not indicative of more oxygen. Also, the amount of oxygen supplied at various settings differs from machine to machine.  In other words, setting 1 does not supply the same amount of oxygen across all POCs and no POC gives 1 liter per minute (lpm) at setting 1 on pulse.  A POC with 6 settings does NOT give 6 liters per minute of oxygen.  A POC with 3 settings does NOT give 3 liters of oxygen.  Use our chart above to see the maximum amount of oxygen each of the listed POCs can give.

Supplemental Oxygen Requires a Prescription

Medical grade oxygen is considered a drug and requires a prescription.  This means that any company you get your POC from should require a prescription.  If you can purchase a POC without one then it is not medical grade and might not give you the amount of oxygen you need.  See FDA statement about requiring a prescription for POCs.

​”Noncentrator” POCs

Be aware that if a POC looks too good to be true, then it probably is. They claim to give up to 4 or 5 liters of oxygen and cost thousands less than the medical grade concentrators.  There are several problems with using these machines though if you need medical supplemental oxygen.  The first is these machines are not FDA approved, so there is no assurance that what you are receiving through the cannula doesn’t contain anything harmful.  The second problem is that as you raise the liter flow you are actually getting less and less oxygen.  This means at 5 liters per minute you are barely getting more oxygen than you get in the surrounding air.

How POCs work

At sea level air is about 78% nitrogen and 21% oxygen.  POCs remove the nitrogen from the air to concentrate and filter the oxygen to what is considered a medical grade level.  The current technology for removing the nitrogen is limited.  Machines can have high liter flow, high concentration of oxygen at all liter flows, or be light weight.  They can’t be all three.

This is why medical grade POCs that are light weight can’t give much oxygen concentrated at 82% or higher above 1 liter per minute.  This is also why “noncentrator” POCs can give upwards of 5 liters per minute and stay light weight.  They might be able to give 1 lpm at around 90% concentration of oxygen, but if you go to 2 lpm the concentration of oxygen drops.  It continues to drop as it goes up each level, until at the highest liter per minute setting you aren’t getting much above room air oxygen concentration.

​Pulse vs. Continuous Flow

The oxygen is delivered in one of two ways.  Either a continuous flow of oxygen, or a pulse.  The continuous flow is just as it sounds – the oxygen is always flowing.  The pulse, or intermittent, method delivers oxygen when it senses the wearer inhaling.  Not everyone can use pulse flow.  The oxygen supply company will typically evaluate whether the patient can use pulse flow.  There are some POCs that can deliver both pulse and continuous.  The type of flow though affects the weight.  Pulse flow can be harder to use when sleeping, and is not recommended for use with CPAP or BiPAP.  The device senses the intake of air from the nose.  If you breathe through your mouth when you sleep then a pulse POC may not deliver what you need.

Pulse

It’s hard to compare pulse to continuous flow.  There’s not a one-to-one correlation.  Much of determining how much oxygen one receives with pulse is dependent on the breathing rate.  The normal breathing rate for adults is around 12-18 breaths per minute (bpm).  When exercising, that rate can increase to 40 bpm or more.  There’s already a lot of information on this page so if you’re interested in a more indepth explanation of pulse and breath rates, along with charts to help approximate a comparison to continuous flow, click here (this link is coming soon).

Pulse Delivery Type

Minute Volume – POCs are only capable of delivering a set amount of oxygen in a minute.  Minute volume delivers a varying amount of oxygen with each breath.  This means the slower your breath rate the more oxygen you will receive with each breath.  When you start breathing faster, you’ll receive less oxygen with each breath.  Within the minute, though, your total amount of oxygen received will be the same.

Fixed Volume – POCs utilizing a fixed volume delivery give a specific amount of oxygen regardless of the breathing rate.  According to the American Association for Respiratory Care’s POC Guide (from 2013), the concentration level of the oxygen may drop if the breath rate is too high.  This means the patient may be getting concentrations below the prescribed range of the given POC, which typically means under 85%.  This is because the machine cannot exceed the amount per minute delivery rate.

Both Minute and Fixed Volume – These POCs deliver a fixed volume, until the breaths per minute (bpm) exceed the devices capacity.  Then it starts using a minute volume, which reduces the amount of oxygen in each breath.​

Weight

​There are two main components that determine the weight of a POC:  the sieve and the battery.  POCs with continuous flow are heavier than pulse.  POCs that only deliver 1 lpm are lighter than 3 lpm POCs.  The batteries on lighter weight POCs may not last as long, or the sieves are smaller, so less liters per minute are delivered.  If you require more than 2 lpm and need continuous flow, a POC might end up weighing more than a tank.

The batteries can also make a difference in the weight.  Some POCs have single and double batteries.  The benefit of the double battery is of course the machine can run longer.  This might add another pound though to the overall weight.

If you are out of the house for an 8 hour period of time and not plugging your machine in to charge, how many additional batteries do you need to take with you?  The additional batteries could end up doubling the overall weight.

Our chart shows the weights as listed by the manufacturers.  Sometimes it’s hard to tell if the weight is the POC only or includes the weight of the battery.