I heard a statement read on the news about this case. They said that there were in fact a dozen oxygen tanks onboard and that they were all operating properly. The intent of those tanks was not lifesaving in the event of an individual passenger having health issues, but rather as part of the entire emergency system of the plane - they were the tanks that would feed oxygen into the masks that would drop down in front of the passengers for which the flight attendants demonstrate proper use.

Because of the issues with her heart rate, the doctor (who was a passenger on the plane) knew that simply administering oxygen was not going to do anything for her. She didn't need oxygen because there wasn't enough oxygen in the plane's air - she needed oxygen because she was going into cardiac arrest and so her heart was not pumping her blood through her lungs. That's not an issue any oxygen tank can fix.

Apparently, though, the physician did try to do some manual procedure with the oxygen tanks, using them in a way entirely different than intended, and attempted to force oxygen oxygen into her lungs manually somehow. If the family saw him attempting something unusual with the O2 tanks, it wasn't because they weren't working or weren't full.

At least, that's what I heard on the news...

Barb, I don't think that rationale holds up. She's right - a plane is not a hospital. Is it good to have lifesaving equipment handy? You betcha. So how far do we take that? Are there kits equipped with tourniquets, defibrillators, ventilators, satellite phones, and flashlights? No. You can't prepare for every emergency, and from the sound of things, the airlines probably aren't required to be prepared for in-flight medical issues that relate to breathing trouble.