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Here is a cautionary tale: A Maryland woman bought a portable oxygen concentrator for her mother, who suffered from chronic obstructive pulmonary disease (COPD).

Somehow, though, the device didn’t seem to be helping. After several months, her mother became confused and lethargic. The family rushed her to an emergency room, where doctors successfully treated her for respiratory failure.

As it turned out, although the patient was using a portable oxygen device, she wasn’t getting enough oxygen. That’s because it was the wrong kind of oxygen concentrator for her condition.

Two types of oxygen tanks

There are two types of oxygen concentrator: pulse-flow (or pulse-dose) oxygen devices and continuous flow delivery devices.

Pulse flow, as the name indicates, provides a pulse or puff of oxygen through a nasal tube when the user inhales. That means if the user is breathing through his or her mouth, that puff may not occur.

A 2017 study by the National Institutes of Health found that pulse flow delivered less oxygen overall than continuous flow. The study of 15 artificial airways concluded that “pulse flow delivered similar, though consistently lower, volume-averaged fraction of inhaled oxygen than steady flow rates equivalent to nominal pulse flow settings.”

Pulse oxygen “gives you about a third of the oxygen that it might normally give you, but it’s giving it to you a little bit smarter,” that is, when you inhale, said Dr. William Han, director of Pulmonary Medicine at Sinai Hospital in Glen Burnie.

“Some patients do just fine on pulse [flow] because that’s all they need,” Han said. But “some patients need more oxygen than the portable oxygen concentrator is able to give them. So, they need to go back to tanks or continuous oxygen.”

If you know someone with a portable oxygen device, make sure they keep track of their oxygen levels. They can do so with a pulse oximetry meter.

These devices, which lightly clip on to the index finger, can detect changes in oxygen saturation levels. It will alert you if your levels are low, whether you’re breathing through your nose or mouth.

Not all doctors know difference

Always check with your doctor about what type of device is right for you. But do your own research too, as not all doctors may know the difference between pulse vs. continuous flow.

Continuous oxygen might be the best solution for people who require a lot, said Dr. Han. “Even people who are mouth breathers who are on continuous oxygen do get oxygen,” he said.

Many people prefer a light, portable device. Unfortunately, most continuous flow devices tend to be heavier. If money permits, some patients may be able to use both types of devices — one at home and one out on the town.

After her frightening trip to the emergency room, the woman has recovered, much to her daughter’s relief.

“Many COPD patients — my mom included — are mouth breathers, and therefore a pulse unit further reduces the delivery of oxygen,” she wrote in an email to the Beacon. “If only I had known about the difference between pulsed and continuous flow oxygen.”