U.S. neurologists are calling on lawmakers to require a uniform definition of when a person is officially brain dead.

The American Academy of Neurology says that “brain death is defined as the death of the individual due to irreversible loss of function of the entire brain” and that such deaths are “equivalent” to circulatory death, which they define as “irreversible loss of function of the circulatory system,” including the heart.

The AAN says it “is not aware of any cases in which following these guidelines led to inaccurate determination of death with return of any brain function, including consciousness, brainstem reflexes or breathing.”

It says its definitions are “widely accepted” by doctors, but so far only Nevada has adopted legislation clarifying what constitutes brain death. As a result, disagreements sometimes arise in court.

Similar court challenges have arisen in Canada. Taquisha McKitty, 27, was declared “dead by neurological criteria” in September 2017 after she suffered a drug overdose in Brampton, Ont. Doctors wanted to take her off life support but the family argued that she was not dead according to their Christian religious beliefs, because her heart continued to beat. They cited the Charter of Rights and Freedoms in court.

An Ontario Superior Court judge ruled against the family, saying the Charter did not apply because McKitty was clinically brain dead. The family was in the process of appealing the decision when McKitty’s heart stopped on New Year’s Eve.

A similar dispute occurred after Shalom Ouanounou suffered a severe asthma attack and was declared brain dead by doctors in September 2017.

Family members argued that, according to Orthodox Judaism, he was still alive so long as his heart was beating and he was breathing. His heart stopped beating at a hospital in Toronto on March 9, before a judge could rule.

With files from The Canadian Press