What is brain death? New guidelines offer answers.

What is brain death? Though the term is used to unhook ventilators and guide organ donation, there hasn't been a single process that determines when brain death has occurred.

That may be about to change: New guidelines may make the process for declaring someone brain dead more uniform. Brain death is a fairly old concept, dating back to the advent of mechanical ventilation and other technologies that can keep a person's body infused with oxygen even as their brain function irrevocably disappears. The first clinical definition of brain death was published in 1968, and the fundamentals still apply: Brain death is diagnosed when the patient loses the capacity for consciousness, shows no brainstem reflexes such as the reaction of the pupils to light, and cannot breathe independently. 

In some high-profile cases, however, family members of a patient do not accept a diagnosis of brain death. In some of these cases, the patient's body can survive for a long time if kept on a ventilator and nourished via feeding tube. In 2013, for example, a 13-year-old California girl named Jahi McMath was declared brain-dead after a routine surgery. McMath's family refused to accept the declaration and instituted a legal battle to keep the child on life support; eventually, the hospital released McMath to her mother, who moved to New Jersey and kept the child on a ventilator and feeding tube. Controversy followed, in part because some doctors claimed she regained signs of brain function such as electrical activity in subsequent years while others argued that there had been no recovery. McMath's kidneys and liver failed in 2018, and she was removed from life support.

Related: 10 things we’ve learned about the brain

The differing opinions in McMath’s case highlights some of the variability in how brain death is determined medically and legally. McMath’s mother moved to New Jersey because while her daughter was legally dead in California, New Jersey has more lenient religious exemptions to the concept of death by neurologic criteria; in New Jersey, McMath was considered alive and could continue to receive insurance-funded healthcare.

Criteria for determining brain death vary from state to state, says Dr. Gene Song Yung, a clinical neurologist at the Keck School of Medicine at the University of Southern California. One 2008 study published in the journal Neurology found that different health centers had variations in the ways they determined brain death, ranging from differences in how the clinical examination to determine brain death was done to what additional testing was performed during the procedure for removing mechanical ventilation to see if the patient could breath on his or her own. 

"That is a problem, because in one respect someone could be declared dead in one location and not dead in another, but also because it leads to a little confusion among the general population and even among doctors about how to determine brain death," Yung told Live Science. 

Clarifying death

Yung led an international effort, the World Brain Death Project, to clarify what brain death is and the basic requirements for determining brain death. Published Aug. 3 in the journal JAMA. The new recommendations define brain death, also known as "death by neurologic criteria" as "the complete and permanent loss of brain function as defined by an unresponsive coma with loss of capacity for consciousness, brainstem reflexes, and the ability to breathe independently." (Critics of the concept of brain death sometimes point to the possibility of brain functions not covered in this definition, such as the secretion of hormones to maintain blood volume. These functions might still occur in some people whose capacity for consciousness and brainstem function are destroyed.) 

While many professional societies and individual health systems have released their own guidelines and procedures, this is the first collaborative international effort between societies to do so.

The recommendations outline the specifics of how to tell if someone meets the criteria for brain death, such as excluding conditions that might mimic the criteria for brain death. For example, someone on a medication that induces paralysis would not show limb movement in response to pain or other similar reflexes. Other steps include ensuring that a sufficient amount of time has passed to make the diagnosis — 24 hours at the very minimum for death caused by lack of oxygen to the brain — and testing a series of basic reflexes controlled by the brainstem. The final test is apnea testing, which determines whether the person can breathe on his or her own, another process controlled by the brainstem. The guidelines also provide the first formal recommendations of how to determine brain death in a person who is being supported by extracorporeal membrane oxygenation (ECMO), a process that circulates the person's blood outside of the body to oxygenate it by machine rather than through the heart and lungs. People on ECMO are not on ventilators, so the usual process of halting ventilation to see if a person can breath on his or her own doesn’t work. Instead, the recommendations call for adjusting the machine so that it doesn’t remove carbon dioxide from the blood on its own. The buildup of carbon dioxide is what triggers inhalation in a living person. If the carbon dioxide buildup doesn’t cause the person to breathe, it is a sign that he or she is dead.

The new guidelines discuss ways for healthcare professionals to handle situations in which a family disagrees with the need to perform a brain-death evaluation or denies the results of such an evaluation. Practitioners should be trained to understand the cultures of the community their hospital serves, and should collaborate with a multidisciplinary team, including spiritual advisors and palliative-care specialists, when dealing with a patient who may be brain dead. In some cases, it might be reasonable to keep the patient on a ventilator for a short period even after the declaration of death is made, such as when family members are traveling to be by the bedside, the recommendations state. However, the guidelines likely won’t end debate over the fundamental nature of brain death, as evidenced by the recommendation that hospital administration attempt to handle disagreements internally rather than escalating to the legal system. More research is needed on why next-of-kin request that a person who has been declared brain-dead remain on a ventilator, and how often such requests are made, the World Brain Death Project authors concluded. 

Despite the rise in new technology, such as functional magnetic resonance imaging (fMRI) that can measure brain activity, the diagnosis of brain death is still best made by a clinical, bedside exam, the World Brain Death Project researchers found. That's because the definition of brain death is centered on the patient's function, says Dr. Claude Hemphill, the division chief of neurology at Zuckerberg San Francisco General Hospital, who was not involved in drafting the recommendations.

"It's based on the person, not on some physiology or anatomy of ‘s there blood flow?’, or 'is there a neuron that's intact somewhere?'" Hemphill told Live Science. 

San Francisco General's procedures for declaring death by neurologic criteria already match the new recommendations closely, Hemphill said, though the hospital may integrate some of the newer guidance, such as the recommendations on ECMO patients. 

The guidance will likely be important for standardizing the diagnosis of brain death across the United States, but will also be particularly useful internationally, said Dr. Jose Suarez, the director of Neurosciences Critical Care at Johns Hopkins University. Many less-developed nations lack criteria for brain death at all, and the new recommendations can aid those countries in developing their own consistent frameworks. 

"We have had a truly international cooperation here, people from all continents bringing their expertise to the matter and agreeing, which is amazing," Suarez, who was not involved in the project, told Live Science. 

Originally published on Live Science.