Mother signs organ donation papers for brain dead son. A day later, he wakes up.

[pnwmom]

36. In my view, the doctor was merely acknowledging the imperfect and imprecise

nature of these determinations. He had clinically diagnosed her as brain dead and an initial brain scan seemed to confirm this -- but, he thought, if his clinical diagnosis was wrong and the boy lived, he would be no more than a vegetable. The doctor turned out to be wrong about that, too.

It also turns out that there is wide variability in the determination of brain deaths. This is from a study last year.

https://www.hindawi.com/journals/neuroscience/2017/6017958/

Objective. Research continues to highlight variability in hospital policy and documentation of brain death. The aim of our study was to characterize how strictly new guidelines of American Academy of Neurology (AAN) for death by neurological criteria were practiced in our hospital prior to appointment of neurointensivists. Method. This is a retrospective study of adults diagnosed as brain dead from 2011 to 2015. Descriptive statistics compared five categories: preclinical testing, neurological examination, apnea tests, ancillary test, and documentation of time of death. Strict adherence to AAN guidelines for brain death determination was determined. Result. 76 patients were included in this study. Preclinical prerequisites were fulfilled in 53.9% and complete neurological examinations were documented in 76.3%. Apnea test was completed in 39.5%. Ancillary test was completed in 29.8%. Accurate documentation of time of death occurred in 59.2%. Overall, strict adherence to current AAN guidelines for death by neurological criteria was correctly documented in 38.2%. Conclusion. Our study shows wide variability in diagnosing brain death. These findings led us to update our death by neurological criteria policy and increase awareness of brain death determination with the goal of improving our documentation following current AAN guidelines.

Here is one set of guidelines, but they say there are alternatives, and this is "opinion based."

http://surgery.med.miami.edu/laora/clinical-operations/brain-death-diagnosis

American Academy of Neurology Guidelines for Brain Death Determination

Many of the details of the clinical neurologic examination to determine brain death cannot be established by evidence-based methods. The detailed brain death evaluation protocol that follows is intended as a useful tool for clinicians. It must be emphasized that this guidance is opinion-based. Alternative protocols may be equally informative.