Joan Rivers has been placed in a medically induced coma, a procedure that suggests she has suffered possible brain damage. (Photo: Getty)

Joan Rivers has been placed in a medically induced coma, a procedure that suggests she has suffered possible brain damage. (Photo: Getty)

Joan Rivers has been put into a medically induce coma, a treatment primarily used to prevent or lessen brain damage in the event of a stroke or blood clot on the brain.

Rivers, 81, went into cardiac arrest today (Aug. 28) while undergoing a surgical procedure, according to law enforcement authorities.

Joan Rivers Rushed to Hospital; Reportedly Stopped Breathing

She was rushed to Mount Sinai Hospital around 10am after she stopped breathing. The cause of her cardiac arrest is unknown. It’s also unknown how long she had stopped breathing.

The brain can go without oxygen for no more than two minutes without starting to suffer substantial damage. The fact that doctors put her into medically induced coma suggests that she has suffered a brain injury.

Medically induced comas are typically reserved for cases involving traumatic brain injury. The goal is to slow down swelling that puts pressure on the brain and causes damage, according to medical references.

In a medically induced coma, the cerebral blood flow is reduced and the blood vessels in the brain shrink. The net effect is to reduce the size of the brain to prevent damage from swelling or a blood clot.

The goal is that with the swelling relieved, the pressure decreases and some or all brain damage may be averted, according to the Journal of Neurotrauma.

The treatment, however, is controversial. Some studies have found little benefit in cases of brain operations, aneurysms, hemorrhaging and stroke.

In other cases, they have proved beneficial.

Rep. Gabriel Giffords was put in a medically induced coma after she was shot in the head during an assault outside a Tucson, Ariz., supermarket in 2011. She survived the attack, although she lost some of her motor functions.

The coma was used to give her brain a chance to heal and reduce swelling to prevent further damage from the wound.

Actress Natasha Richardson died in 2009 after a seemingly minor skiing accident when she developed a blood clot on her brain that caused swelling and led to massive damage.

Doctors are expected to try to bring the 81-year-old comedy icon out of the coma over the weekend, according to The New York Daily News. That will enable them to determine the extent of damage she suffered, if any.

If she survives she could face weeks, if not months, of physical therapy to regain motor skills or she could be permanently impaired.

Earlier today Rivers’ condition was listed as “critical.” But a spokesman for the E! Network, which airs her show “Fashion Police,” said her condition had been upgraded to “stable.”

The latest report, however, suggests that she could be nearer to death than her publicist has let on.