The standard treatment for severe carbon monoxide poisoning relies on pressure chambers that push pressurized oxygen into tissues and blood.

Both the University of Virginia Medical Center and the Duke University Medical Center have hyperbaric chambers for that purpose. The units are used for other medical conditions as well, including smoke inhalation, diabetic wounds that resist healing, and decompression sickness -- "the bends" -- that can afflict scuba divers.

Of the five women who suffered severe carbon monoxide poisoning Sunday at the Collegiate Suites apartments in Blacksburg, three were treated at Duke and two at UVa.

Staff frequently refer to hyperbaric treatment sessions as "dives." Treatment sessions for carbon monoxide poisoning can vary in length, but a typical session at Duke lasts about two hours, said Dr. Bret Stolp, associate professor of anesthesiology and a hyperbaric medicine specialist.

UVa has one chamber. Duke has eight or nine, depending on how they are used.

Poisoning can occur when furnaces, water heaters, internal-combustion engines, space heaters, cooking grills and many other fuel-burners fail to completely convert carbon-containing fuels into carbon dioxide. The carbon monoxide produced instead is highly toxic, colorless and odorless.

In the body, carbon monoxide competes with oxygen by binding strongly to hemoglobin, the molecule in red blood cells that carries oxygen from the lungs to tissues of the body.

"It's a carrying-capacity problem," said Dr. Christopher Holstege, director of UVa's Division of Medical Toxicology and medical director of the Blue Ridge Poison Center.

"Carbon monoxide can affect every organ in the body," Holstege said. "The brain is exceedingly sensitive."

Severe headaches typically accompany exposure to carbon monoxide.

In addition, the heart doesn't pump as well and blood pressure can drop, which is why people pass out, he said. Heart attacks can also occur.

By "washing" hemoglobin molecules of carbon monoxide, the hyperbaric chamber's pressurized oxygen can speed the recovery of poisoning victims and help limit long-term damage to the brain, the heart or other organs, Holstege said.

"We want to decrease the potential for long-term neurological damage," he said. "People who lose consciousness are the ones most at risk."

Stolp treated the three Virginia Tech students who were transferred from Montgomery Regional Hospital in Blacksburg to Duke University Medical Center. He said long-term neurological damage is rare among poisoning victims who receive quick emergency medical attention followed by hyperbaric treatment. He praised the work of first-responders in Blacksburg.

Holstege said young and healthy patients are less likely to suffer long-term effects.

But such effects can occur. UVa's center once treated an accountant who lost the ability to perform some mathematical tasks, Holstege said. Memory can be affected, too, he said.

Whether long-term damage will emerge later is "very hard to predict," he said.

"With family, I tell them, 'Let's wait. Let's see.' "