Brain Death

 Before there was the possibility of organ transplantation, determining that someone was dead could be a relatively leisurely affair. But transplants depend on organs remaining alive after the potential organ donor has died.  If the death is due to irreversible absence of circulation and respiration (Donation after Circulatory Death – DCD), it has to be declared quickly, so that preparation for organ recovery can begin promptly. If the declaration of death is based on brain death, i.e. on irreversible absence of whole brain function (Donation after Death declared by Neurologic Criteria - DDNC), then it must occur while the potential donor is on a ventilator, so that his/her organs continue to be oxygenated.  This means that the declaration of death occurs while the ventilator is still maintaining many of the signs (respiration, heartbeat) that are usually evidence of a living person.  So deciding when someone is brain dead requires both expertise and consensus.

Here's a recent discussion of all this, including some controversy, in JAMA: 

The Uncertain Future of the Determination of Brain Death, by Robert D. Truog, JAMA. 2023;   329(12): 971-972. doi:10.1001/jama.2023.1472

"In 1980, the US Uniform Law Commission (ULC) established the Uniform Determination of Death Act (UDDA), which was subsequently adopted (with some modifications) by all 50 states.1 The law states that death is defined as either (1) the irreversible cessation of circulatory and respiratory functions or (2) the irreversible cessation of all functions of the entire brain, including the brainstem.

...

"The framers of the UDDA rejected the claim that this was a new way of defining death.2 Instead, they pointed to evidence at the time suggesting that the brain is necessary for maintaining biological functioning and that when this brain regulation is absent, homeostatic mechanisms fail, with cardiac arrest invariably occurring within 1 to 2 weeks at most. In other words, brain death and cardiopulmonary arrest were seen as equivalent and equally valid criteria for diagnosing the biological death of a patient.

"However, with improvements in critical care medicine, this equivalency has been called into question. With modern intensive care unit support, some patients can be stabilized and, if provided with mechanical ventilation and tube feedings, their bodies may survive for many years.

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"In fact, patients with brain death may retain most of the capacities of living people, including the ability to absorb nutrition, excrete waste, heal wounds, grow, undergo puberty, and even gestate. This has led many families to reject the diagnosis and insist on the continuation of medical support for their loved ones.

"In addition, a second issue has been that, although the UDDA requires “the irreversible absence of all functions of the entire brain,” the current guidelines from the American Academy of Neurology (AAN) test for only a select number of functions and most notably do not test for hypothalamic functions, which are sometimes present in patients who are diagnosed with brain death

"In the wake of an increasing number of legal challenges related to the determination of brain death, ULC began a process in 2021 to assess whether the UDDA should be revised.1 At least 3 distinct proposals have been considered.

"Proposal 1: Revise the Guidelines to Align With the Current Definition

"One option would be to leave the UDDA intact, but revise the AAN guidelines to include testing for the absence of hypothalamic function.

...

"Proposal 2: Revise the Definition to Align With the Current Guidelines

"A second proposal has been to change the definition of brain death to be in alignment with the guidelines.

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"Revising the UDDA so that it required not the irreversible loss of all brain functions, but rather only those functions that support consciousness and spontaneous respiration, would bring the UDDA into alignment with the AAN guidelines. This approach also has precedent, in that it is the definition that was adopted by the United Kingdom in 2008.

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"Proposal 3: Maintain the Status Quo

"If the position endorsed by commissioner Bopp were to prevail, some states could choose to entirely eliminate the determination of death by neurologic criteria. The impact would be 2-fold: in those states it would no longer be permissible to procure transplantable organs from patients diagnosed with brain death and physicians could be required to continue to provide intensive care unit beds and life support to patients who will never regain consciousness. Such an outcome could have disastrous consequences for our existing systems of organ procurement and transplantation, leading to thousands of otherwise avoidable deaths.

"This has led some commissioners to lean in favor of not making any major revisions to the UDDA, leaving well enough alone."