Will you be checking this suitcase? The Air Carrier Access Act prohibits airlines from charging you fees for mobility equipment and necessary medical supplies carried on board, but says nothing about checked bags.

Individual airlines have additional polices (for example, Lufthansa permits you to check up to two wheelchairs at no additional charge).

I didn't see anything specific to this effect on the American Airlines website either - I'd suggest you call AA up and ask to speak to a Special Assistance Coordinator to ask about any charge for checking that bag.

You might also consider ordering supplies and having them shipped to your hotel or wherever you're staying ahead of time.