One of the most confusing aspects of portable oxygen concentrators (POCs) is the pulse settings. Are they the same as continuous flow settings? Is there a difference in the setting from one POC to another? I am going to provide a detailed response to these common questions. Be warned! Since this is such important information, this post is longer than usual because I wanted to be sure all the information is in one place.
On an oxygen cylinder or home oxygen concentrator, a setting 3 LPM provides 3 liters per minute, or 3,000 milliliters, of actual oxygen output. However, the average breathing rate is 20 breaths per minute, or once every 3 seconds. Therefore, an oxygen user only inhales about 1/3 of the output, or 1,000 mL. The science and math behind an oxygen conserver recognize that 2/3 of the oxygen is wasted, so if it is provided only when the user is inhaling, the oxygen can be conserved. When an oxygen conserver is used on an oxygen cylinder, it simply makes the oxygen last longer; when put into a portable oxygen concentrator (POC), it allows the unit to be smaller and the batteries to last longer.
The amount of oxygen output and the actual amount a patient receives on the various pulse settings depends on several factors.
The first is the conserving ratio of the conserver that is used. Conservers use a 3:1 to 6:1 ratio, with the 3:1 ratio providing the largest amount of oxygen, and 6:1 providing the smallest amount of oxygen. When a conserver is used on an oxygen cylinder, a 3:1 ratio will allow the cylinder to last 3 times longer; a 6:1 ratio conserver will allow the cylinder to last 6 times longer.
In simplest terms, a conserver with a 3:1 ratio provides, in pulse doses, 1/3 the amount of the oxygen of the setting used. At 3 LPM, it provides 1 LPM, or 1,000 mL – the same amount of oxygen the average person would naturally inhale at 20 breaths per minute! I have provided a table of the pulse flow output using various conserve ratios:
|1 LPM||2 LPM||3 LPM|
|3:1 RATIO||333 mL||667 mL||1,000 mL|
|4:1 RATIO||250 mL||500 mL||750 mL|
|5:1 RATIO||200 mL||400 mL||600 mL|
Seems pretty straightforward, but it gets more complicated.
Another factor that determines oxygen output is the delivery method of the conserver. There are actually five common delivery methods:
- Pulse – this method delivers a fixed amount of oxygen each time it detects inhalation. As soon as it delivers the oxygen, it stops until the person takes another breath. All electronic conservers use this method of delivery.
- Demand – this method delivers oxygen as soon as it detects inhalation and then uses continuous flow until the user exhales. Dual-lumen conservers use this delivery method.
- Hybrid – this method delivers a pulse at the beginning and then uses declining continuous flow until the user exhales. Many pneumatic conservers use this method.
- Minute Volume – this method delivers a fixed amount of oxygen per minute. The amount of oxygen delivered with each breath depends on the breathing rate of the user. Slower breathing rate equals larger amount of oxygen per breath; faster breathing rate equals smaller amount of oxygen per breath.
- Uniform Pulse – this method delivers the same amount of oxygen with every breath, regardless of the breathing rate. Slower breathing rate equals less oxygen over the course of a minute; faster breathing rate equals more oxygen over the course of a minute.
Many people interested in a POC already use a conserver on their oxygen cylinders. Let’s look at some popular conservers:
- Chad Evolution – 5:1 ratio, electronic conserver, pulse delivery, uniform pulse delivery up to 40 breaths per minute
- Chad Bonsai – up to 6:1 ratio, pneumatic conserver, hybrid delivery, uniform pulse delivery up to 40 breaths per minute
- Drive SmartDose – unknown ratio, electronic conserver, pulse delivery, uniform pulse delivery
- Invacare Element – 3.5:1 ratio, pneumatic conserver. uniform pulse delivery up to 40 breaths per minute
- Medline EconO2mizer – 5.7:1 ratio (at 2 LPM), pneumatic conserver, hybrid delivery
Now let’s look at popular portable oxygen concentrators. First, some POCs provide both continuous and pulse flow options, while some only offer pulse flow. When not in continuous flow, all POCs use an electronic conserver that is built into the unit, thus all POCs use a pulse delivery method. Since actual conserve ratios are not provided by the manufacturers, I am giving a rough ratio based on the detailed information of oxygen delivered per breath found at OxiMedical.com.
- DeVilbiss iGo, Invacare Solo2, Oxlife Independence, SeQual Eclipse 3 – all of these units provide roughly a 3:1 ratio, uniform pulse delivery (I am not certain if this is up to 40 breaths per minute; however, I have never heard of anyone out-breathing one of these larger, more powerful POCs)
- Respironics SimplyGo – roughly a 4:1 ratio, uniform pulse delivery up to 40 breaths per minute for setting 1-4, 30 breaths per minute for setting 5, and 20 breaths per minute for setting 6
- Respironics EverGo (the SimplyGo’s predecessor – discontinued, but still available from some dealers) – roughly a 4:1 ratio, uniform pulse delivery up to 20 breaths per minute for setting 1-4 and up to 15 breaths per minute for settings 5-6 (patient can easily out-breathe the unit at settings 5 and 6 when breathing faster than 20 breaths per minute)
- Inogen One G2 and G3, Invacare XPO2 – roughly a 5:1 ratio, minute volume delivery
- AirSep FreeStyle, LifeChoice Activox – roughly a 6:1 ratio, minute volume delivery
When all is said and done, most people can use the SAME pulse flow setting as they do continuous flow setting. Some find that they need to bump up the setting a notch or two, especially on the smaller POCs that have a 5:1 or 6:1 ratio. Since so many factors contribute to the actual amount of oxygen inhaled, the flow setting number is sometimes just a number. The actual amount of oxygen needed is simply what it takes to raise the blood oxygen percentage to an acceptable level as directed by a physician. A fingertip pulse oximeter provides the numbers that are most important.