Nitric Oxide (or nitrous) is an anesthetic intended to dull consciousness or put someone to sleep. It is, I believe, sometimes used with infants due to dangers specific to newborns if pure oxygen is given to them. Excessive concentrations of O2 can cause blindness and other harm in very young newborns, and especially in "preemies."

If the problem is "insufficient oxygen" supplemental pure oxygen is often prescribed for other than infants. (This treatment is often used for people with emphysema and/or other lung deterioration.)

Oxygen bottles of compressed O2 and/or liquid oxygen (LOX) are still used, but of course require delivery of fresh cans at regular increments. The LOX supplies also generally require "conditioners" to warm the flow and can range from simple to "gottabeanengineer" to maintain them.

The more common supplement now uses an "oxygen concentrator" that blows air through an absorbent that removes the nitrogen and provides an output flow of very pure oxygen. The flow is reversed, and when air is blown back through at a different pressure the nitrogen is removed from the absorbent so that it can be recycled to repeat. A pair of absorbent cans run in alternation, with one making oxygen while the other is being replenished, so that the oxygen output is continuous.

With a prescripton, Medicare normally will pay for nearly all the cost of renting one of these, although there may be a "deductible" on this particular equipment since a "rental" is treated a little differently than a purchase. Other insurers may vary - a lot. Usually a single physician's order suffices indefinitely, since the device is most often considered to be for a "permanent ailment."

Portable O2 concentrators are available, but the weight of the required battery might make one difficult for an elderly patient to carry, and of course they require recharging and maintenance of batteries. The line powered units do produce some noise, but most people don't have difficulty sleeping with one once they've become accustomed, but I don't have direct observations for a portable.

The oxygen usually is directed into the nose with a light "nasal canula" that pokes a little nozzle barely into each nostril. Most people tolerate the plumbing easily although some (elders especially) are "annoyed" with the device and may need watching to make sure it stays in place.

"Low Oxygen" can also be caused by low hemoglobin (anemia) and that's fairly common in the elderly. The anemia can sometimes be controlled with a modified diet and/or with "iron supplements" but many elderly don't tolerate the iron pills well and maintaining ideal diets can be a separate (and difficult) problem. The prior use of transfusions suggests (to me, a non-expert) that in this case the PsO2 problem may be anemia-related rather than diminished lung oxygenation capacity, although one can be affected by both at the same time.

My experience is that true "low oxygen" can only be determined by a fairly complex serological (blood) test that most (of my) doctors seem reluctant to prescribe. Diagnosis usually is based on "symptoms" which usually is accurate enough but can mislead (whether rarely as they say, or fairly often, I don't know).

Assuming she has a regular physician, it might be worth asking:

"Would supplemental oxygen be helpful for her?"

and

"Is she anemic and can we do anything about it?"

You might not get a direct answer on either, but might still get some clues to things you might try.

John