The observation period after clinical brain death diagnosis according to ancillary tests: differences between supratentorial and infratentorial brain injury

The reticular activating system: a narrative review of discovery, evolving understanding, and relevance to current formulations of brain death

A series of landmark experiments conducted throughout the 20th century progressively localized the regions involved in consciousness to the reticular activating system (RAS) and its ascending projections. The first description of the RAS emerged in 1949 through seminal experiments performed by Moruzzi and Magoun in feline brainstems; additional experiments in the 1950s revealed connections between the RAS and the thalamus and neocortical structures. This knowledge has allowed for the explanation of disorders of consciousness with exquisite anatomic precision. The clinical relevance of the RAS is further apparent in modern definitions of brain death/death by neurologic criteria (BD/DNC), which require demonstration of the complete and permanent loss of capacity for consciousness as one of their core criteria. BD/DNC is currently understood across jurisdictions in terms of "whole brain" and "brainstem" formulations. Although their clinical examination between formulations is indistinguishable, policies for BD/DNC declaration may differ in the rare scenario of patients with isolated infratentorial brain injuries, in which ancillary testing is advised in the whole brain formulation but not the brainstem formulation. Canadian guidelines acknowledge that the distinction between whole brain and brainstem formulations is unclear with respect to clinical implications for patients with isolated infratentorial injuries. This has led to variability in Canadian clinicians' use of ancillary testing when the mechanism of BD/DNC is suspected to be an isolated infratentorial injury. The present narrative review highlights these concepts and explores implications for determination of BD/DNC in Canada, with specific emphasis on the RAS and its relevance to both formulations.

Infratentorial Brain Injury Among Patients Suspected of Death by Neurologic Criteria: A Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVES

There is a paucity of data on the frequency and prognosis of infratentorial brain injury among patients suspected of death by neurologic criteria (DNC), which likely contributes to scientific uncertainty regarding the role of isolated brainstem death in DNC determination. Our aim was to synthesize the prevalence, characteristics, and evolution of infratentorial brain injury, including isolated brainstem death, among patients suspected of DNC.

METHODS

We conducted a systematic review by searching Medline, Embase, EBM Reviews, CINAHL Complete, and the gray literature from inception to March 26, 2021. We selected cohort and cross-sectional studies, case reports, and case series that included patients suspected of DNC. Two study investigators independently performed study selection, data collection, and risk of bias assessment. Our primary outcomes were the respective prevalence of infratentorial brain injury and isolated brainstem death, which we meta-analyzed using mixed-effects Bayesian hierarchical models with diffuse priors. Our secondary outcomes were the characteristics and evolution of patients with infratentorial brain injury and isolated brainstem death.

RESULTS

Twenty-one studies met the selection criteria, most of which were of moderate to high risk of bias. Among patients suspected of DNC, the prevalence of infratentorial brain injury ranged from 2% to 16% (n = 3,602, mean prevalence: 6.3%, 95% highest density interval [2.4%-14.2%]), whereas the prevalence of isolated brainstem death ranged from 1% to 4% (n = 3,692, mean prevalence: 1.5%, 95% highest density interval [0.5%-3.9%]). A total of 38 isolated brainstem death cases with data on clinical characteristics and/or evolution were included. All had infratentorial strokes. Twenty patients had EEG background activity in the α or θ frequencies, 19 had preserved cerebral blood flow, 2 had preserved supratentorial cerebral perfusion, 2 had cortical responses to visual evoked potentials, and 1 had cortical responses to somatosensory evoked potentials. At the latest follow-up, 28 had progressed to whole-brain death.

DISCUSSION

Studies with moderate to high risk of bias suggest that infratentorial brain injury is relatively uncommon among patients suspected of DNC. Isolated brainstem death is rarer and seems to carry a high risk of progression to whole-brain death. These findings require further high-quality investigation.

Neurological Determination of Death Following Infratentorial Stroke: A Population-Based Cohort Study

BACKGROUND

There is international variability in whether neurological determination of death (NDD) is conceptually defined based on permanent loss of brainstem function or "whole brain death." Canadian guidelines are not definitive. Patients with infratentorial stroke may meet clinical criteria for NDD despite persistent cerebral blood flow (CBF) and relative absence of supratentorial injury.

METHODS

We performed a multicenter cohort study involving patients that died from ischemic or hemorrhagic stroke in Alberta intensive care units from 2013 to 2019, focusing on those with infratentorial involvement. Medical records were reviewed to determine the incidence and proportion of patients that met clinical criteria for NDD; whether ancillary testing was performed; and if so, whether this demonstrated the absence of CBF.

RESULTS

There were 95 (27%) deaths from infratentorial and 263 (73%) from supratentorial stroke. Sixteen patients (17%) with infratentorial stroke had neurological examination consistent with NDD (0.55 cases per million per year). Among patients that underwent confirmatory evaluation for NDD with an apnea test, ancillary test (radionuclide scan), or both, ancillary testing was more common with infratentorial compared with supratentorial stroke (10/12 (85%) vs. 25/47 (53%), p = 0.04). Persistent CBF was detected in 6/10 (60%) patients with infratentorial compared with 0/25 with supratentorial stroke (p = 0.0001).

CONCLUSIONS

Infratentorial stroke leading to clinical criteria for NDD occurs with an annual incidence of about 0.55 per million. There is variability in clinicians' use of ancillary testing. Persistent CBF was detected in more than half of patients that underwent radionuclide scans. Canadian consensus is needed to guide clinical practice.

A review of current controversies in determining death by neurologic criteria in children

PURPOSE OF REVIEW

Death by neurologic criteria (DNC) is the irreversible cessation of all functions of the entire brain, including the brainstem. It is legally recognized as equivalent to cardiopulmonary death. Legal and ethical controversies surrounding DNC have emerged as a result of several highly publicized cases that have eroded public trust in our ability to declare DNC accurately. In this review, we focus on recently published primary data about DNC and address some of these controversies.

RECENT FINDINGS

Approximately 21% of children who die in pediatric intensive care units (PICU) are declared DNC. Although 60% of physicians report that they have been asked to maintain organ support after DNC declaration, less than 1% of patients remain physically present in the PICU more than 5 days after DNC declaration. We discuss strategies for safely conducting the apnea test, indications and prevalence of ancillary testing, and objections to DNC, including issues of consent and requests for ongoing organ support.

SUMMARY

In order to maintain public trust, published guidelines must be followed to accurately and consistently diagnose DNC. We must develop strategies to respond to objections to DNC determination. Ongoing research is needed to improve the safety of apnea testing and indications for and interpretation of ancillary testing.