Anne Heche legally dead following car crash: What is anoxic brain injury?

Actor Anne Heche is legally dead after suffering from a "severe anoxic brain injury" due to a car accident in Los Angeles last week, according to a statement from her spokesperson.

While her heart is still beating, she's legally dead according to California law, the spokesperson said in a statement obtained by TODAY. She has yet to be taken off life support in case she might be a match for an organ donation.

Late Thursday, a spokesperson for the star shared that she had "suffered a severe anoxic brain injury" due to last Friday's car accident, remained in critical condition and wasn't expected to survive. "It has long been her choice to donate her organs and she is being kept on life support to determine if any are viable," the statement read.

The accident occurred on Aug. 5, police told Los Angeles NBC affiliate KNBC. It involved a Mini Cooper speeding down a residential street into a home. The crash caused a "heavy fire" that took almost an hour to put out, officials said.

On Thursday, a Los Angeles police spokesperson told NBC News that Heche's "blood draw revealed the presence of drugs" and that the case is being investigated as a felony DUI traffic collision. But the spokesperson clarified that investigators planned to test her blood a second time to "rule out any substance/medication administered at the hospital." The LAPD spokesperson said that he could not yet comment on the presence of cocaine, fentanyl or alcohol.

An LAPD statement issued later on Thursday reiterated that the department was awaiting "final toxicology results" and that the investigation was ongoing. A spokesperson for Heche declined to comment on the preliminary testing.

Traumatic injuries and drug overdoses are common causes of anoxic brain injuries, NBC News senior medical correspondent Dr. John Torres told TODAY.

What is an anoxic brain injury?

An anoxic brain injury refers to when there is a lack of oxygen to parts of the brain, Torres explained. This can occur for a range of reasons, such as a stroke, drug overdose, heart attack, drowning or trauma (an injury to the body).

"If that happens, the brain cells die because they need oxygen. ... Brain cells do not regrow," Torres said. "Once you get that brain injury, that brain injury is more or less permanent."

Can you recover from anoxic brain injury?

Generally speaking, anoxic brain injury usually "results in permanent brain damage and severe disability, if not death," Dr. Eric Cioe-Pena, an emergency medicine physician and Northwell Health in Staten Island, New York, told TODAY. "Prognosis from the injury is usually poor."

The larger the area of the brain that did not receive oxygen, the lesser the chances of survival. "If it's a large brain injury site, then your chances of recovery are zero or very rare," Torres said.

Patients with an anoxic brain injury may recover to a state where they're in a coma or persistent vegetative state, he added, but it's rare that they'll return to a state where they're fully functional.

How common are anoxic brain injuries?

Anoxic brain injuries are "probably more common than people think," Torres said, pointing out that they often occur in heart attacks, strokes or drug overdoses, which are on the rise. "What's typically not as common are the larger ones because people typically pass away from those fairly quickly," he added.

Cioe-Pena stressed that drowning is one of the most common causes of anoxic brain injury in young, healthy people and that anoxic brain injuries can sometimes be prevented with bystander CPR.

"Hands-only compression can oxygenate the brain while help arrives," he said.

Heche is known for starring in soap opera "Another World" in the late '80s and early '90s and her roles in the films “Donnie Brasco,” “Volcano,” and “I Know What You Did Last Summer.” She has two sons, Homer Laffoon, 20, and Atlas Heche Tupper, 11.

“We have lost a bright light, a kind and most joyful soul, a loving mother, and a loyal friend,” Heche’s family said in a statement. “Anne will be deeply missed but she lives on through her beautiful sons, her iconic body of work, and her passionate advocacy. Her bravery for always standing in her truth, spreading her message of love and acceptance, will continue to have a lasting impact.