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.

Clinical evaluation and ancillary testing for the diagnosis of death by neurologic criteria: a cross-sectional survey of Canadian intensivists

PURPOSE

Trust in the deceased organ donation process relies on the expectation that the diagnosis of death by neurologic criteria (DNC) is accurate and reliable. The objective of this study was to assess the perceptions and approaches to DNC diagnosis among Canadian intensivists.

METHODS

We conducted a self-administered, online, cross-sectional survey of Canadian intensivists. Our sampling frame included all intensivists practicing in Canadian institutions. Results are reported using descriptive statistics.

RESULTS

Among 550 identified intensivists, 249 (45%) completed the survey. Respondents indicated they would be comfortable diagnosing DNC based on clinical criteria alone in cases where there is movement in response to stimulation (119/248; 48%); inability to evaluate upper/lower extremity responses (84/249; 34%); spontaneous peripheral movement (76/249; 31%); inability to evaluate both oculocephalic and oculo-caloric reflexes (40/249; 16%); presence of high cervical spinal cord injury (40/249; 16%); and within 24 hr of hypoxemic-ischemic brain injury (38/247; 15%). Most respondents agreed that an ancillary test should always be conducted when a complete clinical evaluation is impossible (225/241; 93%); when there is possibility of a residual sedative effect (216/242; 89%); when the mechanism for brain injury is unclear (172/241; 71%); and if isolated brainstem injury is suspected (142/242; 59%). Sixty-six percent (158/241) believed that ancillary tests are sensitive and 55% (132/241) that they are specific for DNC. Respondents considered the following ancillary tests useful for DNC: four-vessel conventional angiography (211/241; 88%), nuclear imaging (179/240; 75%), computed tomography (CT) angiography (156/240; 65%), and CT perfusion (134/240; 56%).

CONCLUSION

There is variability in perceptions and approaches to DNC diagnosis among Canadian intensivists, and some practices are inconsistent with national recommendations.

Requests for somatic support after neurologic death determination: Canadian physician experiences

PURPOSE

Neurologic determination of death (NDD) is legally accepted as death in Canada but remains susceptible to misunderstandings. In some cases, families request continued organ support after NDD. Conflicts can escalate to formal legal challenges, causing emotional, financial, and moral distress for all involved. We describe prevalence, characteristics, and common experiences with requests for continued organ support following NDD in Canada.

METHODS

Mixed-methods design combining anonymous online survey with semi-structured interviews of Canadian critical care physicians (448 practitioners, adult and pediatric).

RESULTS

One hundred and six physicians responded to the survey and 12 participated in an interview. Fifty-two percent (55/106) of respondents had encountered a request for continued organ support after NDD within two years, 47% (26/55) of which involved threat of legal action. Requests for continued support following NDD ranged from appeals for time for family to gather before ventilator removal to disagreement with the concept of NDD. Common responses to requests included: consultation with an additional physician (54%), consultation with spiritual services (41%), and delay of one to three days for NDD acceptance (49%). Respondents with prior experience were less likely to recommend ancillary tests (P = 0.004) or consultation with bioethics services (P = 0.004). Qualitative analysis revealed perceptions that requests for continued organ support were driven by mistrust, tensions surrounding decision-making, and cultural differences rather than a lack of specific information about NDD.

CONCLUSIONS

Family requests for continued somatic support following NDD were encountered by half our sample of Canadian critical care physicians. Mitigation strategies require attention to the multifaceted social contexts surrounding these complex scenarios.