oxygen tent

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A canopy placed over the head and shoulders or over the entire body of a patient to provide oxygen at a higher level than normal.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun medicine A canopy for the head and shoulders, or a similar enclosure for the whole body, within which air having a higher than normal supply of oxygen can be administered to a patient.