My hypothesis is: what if he's not?
One idea that Lucas was purported to consider was that Palpatine could control Vader in a quite literal physical sense. The idea was that Palpatine had, at the time of Vader's reconstruction, placed an implant at the base of his skull in order to do so. There was no practical way of demonstrating this bit of trivia in the course of the reconstruction scene, as it would be superfluous to the rest of the story. However, that doesn't mean some EU author won't come across it and run with it at a future date.
Also, it might be of interest to note that hyperbaric chambers are in use today for burn victims. Hyperbaric oxygen therapy (HBO therapy or HBOT) is helpful for treating people exposed to smoke inhalation, soft tissue infections and radiation. The treatment of burn victims seems to still be antidotal, although it is frequently used for those who undergo skin grafts.
Here's some great info I lifted from the Dr. Joseph F. Smith Medical library online (which, for some reason, I can't actually get to anymore) that folks may find helpful with their fan fictions:
Oxygen therapy is a form of treatment that uses oxygen in elemental or compound forms to heal various disease conditions and strengthen the immune system. Hyperbaric oxygen therapy (HBO) is a mainstream treatment that involves placing the patient in a pressurized chamber with pure oxygen (O2).
The purpose of HBO therapy is the reversal of conditions or processes caused by inadequate oxygen in the body (e.g., asthma, carbon monoxide poisoning, smoke inhalation, decompression sickness, and mountain sickness); or the speeding-up of healing in traumatic injuries or infections by increasing the amount of oxygen present in body tissues (e.g., crush injuries, skin grafts, soft tissue infections, bone inflammation, or damage caused to bone and soft tissue by radiation therapy).
HBO is not given to patients with untreated pneumothorax, a condition in which air or gas is present in the cavity surrounding the lungs. It is also not used for premature infants, because of the risk of retrolental fibroplasia, a condition in which the blood vessels in the retina of the infant's eye do not develop normally. Retrolental fibroplasia can cause blindness in children born prematurely.
HBO is used cautiously in patients with a history of pneumothorax, chest surgery, emphysema, middle ear surgery, uncontrolled high fevers, upper respiratory infections, seizure disorders, or hereditary disorders of the red blood cells.
In HBO therapy, the patient is placed in a pressurized chamber in which he or she breathes pure oxygen within the chamber itself or administered through a mask, head tent, or endotracheal tube. A tight-fitting aviator or anesthesia mask is used for patients with carbon monoxide or smoke inhalation poisoning. The "rebreather" masks commonly used in hospital emergency rooms do not fit tightly enough for patients with carbon monoxide or smoke inhalation injuries and should not be used with them.
A nasal cannula or catheter may be used for small infants who need oxygen therapy for lung diseases because it allows them more freedom of movement. Otherwise, endotracheal tubes or anesthesia masks can be used with children as well as adults.
The length of time in the oxygen chamber, the degree of pressurization, and the number of treatments depend on the condition being treated. Decompression sickness from diving accidents may require up to two weeks of oxygen treatment. Patients with gas gangrene are given seven treatments over a three-day period. Skin graft patients are given two treatments daily for three to seven days. Patients with osteomyelitis may require as many as 40 to 60 treatments. Most treatment sessions for most conditions are 90 minutes in length, with one or two five-minute "air breaks" at 20-minute or half-hour intervals. Pressures are usually 2.5 or 3 ATA (atmospheres absolute).
HBO therapy appears to be effective in treating burn injuries, but has not been studied widely enough to be universally used by doctors.
Risks associated with hyperbaric oxygen treatment include seizures, irritation of the inner ear, numbness in the fingers, and temporary changes in the lens of the eye. In rare cases, HBO causes inflammation of the optic nerve that may lead to blindness.
Normal results of HBO therapy are recovery from the disease condition and resolution of side effects (if any) of hyperbaric oxygen.