https://blogs.scientificamerican.com/observations/what-is-death-exactly/

Pronouncing a patient dead in a hospital seems relatively simple: palpate for lack of pulse, determine that the patient's neurological function is absent, then disclose, out loud, his or her full name and the time of death. Except it isn’t that simple at all—in the inpatient setting.

The difference between dead and alive can be straightforward to delineate in the right context. There are professions for which this skill is absolutely paramount. Think of soldiers in the middle of a battlefield, war photojournalists or field-trauma EMTs at the site of a multiple-vehicle crash: each has to make quick, decisive pronouncements about a person’s viability to do his or her job effectively, and the verdict is based on a mix of available objective data and personal experience. The inpatient hospital setting is a much more controlled environment, so you’d expect the protocols for death pronouncement to be that much more standardized. But they are hardly uniform.