I had a 17-year-old Mini Dachshund named Scrappy. She had CHF and occasionally experienced pulmonary edema, at which point she required oxygen at the vet’s. The first time it cost me $3000 for her to stay and be treated for two nights. She was worth it.
The vet had her on 34% O2 in an air tight compartment. I resolved to find a way to give her oxygen at home, because I couldn’t afford to take her to the vet again. I couldn’t rent human oxygen tanks without a prescription. So I got Nitrox certified and rented 34% mix tanks from the SCUBA shop next door to my apartment.
When she needed to be put on O2, I would take the shelves out of the dishwasher, duct tape over the vents and put her inside with the opening covered with plexiglass and my regulator inside on a slow leak. It worked.