Flow is not perfusion, and perfusion is not function: ancillary testing for the diagnosis of brain death

A red flag for diagnosing brain death: decompressive craniectomy of the posterior fossa

“…Instead, the demonstration of complete cerebral circulatory arrest, along with the clinical findings of BD/DNC, reliably excludes recovery of brain function. 8 , 15 Cerebral circulatory arrest is the consequence of a supercritical increase of ICP. Preventing a posterior fossa ICP increase by suboccipital craniectomy allows blood supply to the lower brainstem, which is a prerequisite of apnea reversal.…”

The capacity for consciousness and the clinical diagnosis of brain death: are we using the correct gold standard?

“…1 The 2020 World Brain Death Project ''…only requires the demonstration of the absence of brainstem function essential for consciousness and other vital functions such as autonomous breathing'' for the clinical diagnosis of brain death. 2 Plourde et al elaborated on the pathophysiologic significance of absent brain function with persistent intracranial blood flow and capillary perfusion to highlight the limited utility and pitfalls of ancillary tests in comparison with the gold standard of physical examination in the clinical diagnosis of brain death. 2 They emphasize that death diagnosis ''…by neurologic criteria is fundamentally a clinical determination based on the permanent absence of capacity for consciousness and brainstem areflexia'' [emphasis added].…”

“…2 Plourde et al elaborated on the pathophysiologic significance of absent brain function with persistent intracranial blood flow and capillary perfusion to highlight the limited utility and pitfalls of ancillary tests in comparison with the gold standard of physical examination in the clinical diagnosis of brain death. 2 They emphasize that death diagnosis ''…by neurologic criteria is fundamentally a clinical determination based on the permanent absence of capacity for consciousness and brainstem areflexia'' [emphasis added]. 2 Nevertheless, the authors do not acknowledge that neurologic physical findings on clinical examination of motor unresponsiveness to external stimuli, cessation of cranial nerve (brainstem) reflexes, and spontaneous breathing have never been scientifically validated to accurately exclude the capacity for internal and external conscious awareness in humans.…”

“…2 They emphasize that death diagnosis ''…by neurologic criteria is fundamentally a clinical determination based on the permanent absence of capacity for consciousness and brainstem areflexia'' [emphasis added]. 2 Nevertheless, the authors do not acknowledge that neurologic physical findings on clinical examination of motor unresponsiveness to external stimuli, cessation of cranial nerve (brainstem) reflexes, and spontaneous breathing have never been scientifically validated to accurately exclude the capacity for internal and external conscious awareness in humans. To the contrary, a previous case suggests the possibility that clinical tests showing loss of certain brain functions such as behavioural motor responsiveness, cranial nerve reflexes, and spontaneous breathing can be associated with preservation of residual conscious awareness and minimally conscious state.…”

In reply: The capacity for consciousness and the clinical diagnosis of brain death: are we using the correct gold standard?

“…1 The goal of our commentary was not to question the validity of the established criteria, but rather to offer an appraisal of available ancillary tests relative to the current definition of death by neurologic criteria (DNC) as accepted in 2021, as well as a necessary distinction between cerebral flow, perfusion, and function. 2,3 We recognize the challenges and pitfalls associated with the use of neuroimaging and clinical examination for definitive determination of brain death, but they remain the only bedside tools available to the clinician. Although autopsy studies may provide confirmation of structural neuronal damage, they hardly represent a useful aid to diagnosis in a comatose patient.…”