• Eugene Park, Elaine Liu, Sam D Shemie, and Andrew J Baker.
• Keenan Research Centre for Biomedical Science in the Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, ON, Canada.
• Neurocrit Care. 2018 Feb 1; 28 (1): 133-141.

BackgroundDeath after withdrawal of mechanical ventilation frequently follows the sequence of progressive hypoxemia and hypotension leading to cardiac arrest. Accurate timing of the determination of death is fundamental to trust in controlled donation after circulatory death (cDCD) programs and is generally based on cessation of circulation (pulselessness), brain function (apnea), and the passage of time. If death is understood to be the unresuscitatable loss of brain function, the clinical determination that death following apnea and pulselessness has occurred is largely inferential. We sought to elucidate the relationship between the available clinical variables and the loss of brain function and its inability to be resuscitated.MethodsWe developed a rat model of progressive hypoxia resulting in apnea and circulatory failure. We monitored clinical physiological variables including heart rate, respiration, and arterial pulse pressure. In addition, we simultaneously monitored spontaneous and evoked brain activity within the hippocampus through microelectrode field potential recordings. We also examined neurological function following restoration of pulmonary and circulatory function.ResultsOur data provide evidence that in a model of progressive hypoxemia, loss of spontaneous and evoked brain activity preceded the loss of circulation. Importantly, the data suggest that the loss of brain function, in the presence of restored cardiopulmonary indices, occurred at a time point after apnea but before the loss of detectable arterial pulse pressure.ConclusionsThese are important data that act as a conceptual reference point when clinicians undertake the inferential activity of identifying the time prior to which a patient has died following progressive hypoxemia and while observing apnea and pulselessness.

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