Cerebral <scp>CT</scp> angiography as an ancillary investigation to support a clinical diagnosis of death using neurological criteria: a reply

We thank our colleagues [1] for their support of the CT Angiography Consensus Guideline to support a clinical diagnosis of death using neurological criteria [2]. Since the 1970s the UK has championed a brain-based definition of death. Subsequent UK Codes of Practice clarified the functions whose loss would indicate that death has occurred: namely the capacity for consciousness and breathing. There is increasing worldwide convergence around this functional definition that also emphasises the importance of the brainstem [3, 4]. The authors draw attention to international differences in confirming death using neurological criteria when caused by isolated infratentorial brain pathology. The Academy of Medical Royal Colleges allows confirmation of death using neurological criteria in this setting. However, these patients require diagnostic caution. Recent Canadian guidance that “Infratentorial brain injury without significant supratentorial involvements does not fulfil Death using Neurological Criteria and requires ancillary investigation” [4] is somewhat confusing: if there is supratentorial involvement then, by definition, there is no isolated infratentorial brain pathology. Similarly, if ancillary investigation does not demonstrate blood flow, hypoxic supratentorial insult should be visible on plain CT. Since most patients with isolated infratentorial brain pathology will develop hydrocephalus and supratentorial injury over a few days [5], the guidance could simply recommend delaying the diagnosis death using neurological criteria confirmation until supratentorial involvement develops. From a UK perspective, we hope the following observations prove helpful. The Academy of Medical Royal Colleges Code allows doctors to confirm death using neurological criteria in isolated infratentorial brain pathology but we recommend extra caution as recommended by the nationally endorsed testing forms. Further investigations, allowing extra time or using an ancillary test, may be appropriate. Legally, the House of Lords (now the Supreme Court) accepted the loss of brainstem function as death since 1993, and subsequent case law has upheld this decision [6]. The planned update to the Code of Practice (due 2024) is unlikely to change long-established and accepted UK practice. Isolated infratentorial brain pathology was not involved in any of the recent high-profile cases questioning the diagnosis. There is no reason to doubt the caution UK clinicians employ when diagnosing death using neurological criteria in isolated infratentorial brain pathology. Hopefully, the updated code will provide further guidance on the approach required. We expect CT angiography to be increasingly utilised to support a clinical diagnosis of death using neurological criteria. However, clinicians need to be aware of the following important caveats [2]: its sensitivity of 85% means that 15% of patients with a diagnosis of death using neurological criteria have demonstratable intracranial vessel opacification even when the diagnosis is primarily supratentorial pathology. Lack of flow on CT angiography is used as a surrogate for absent function supporting both the Canadian and UK definition of death, which is based on loss of brain function rather than loss of brain blood flow per se. It is, therefore, possible to confirm death in both countries despite the persistence of some brain blood flow. This is why CT angiography (or any ancillary investigation) is not mandated in either country when there are no confounding factors. The quoted 100% specificity of CT angiography in death using neurological criteria is reassuring, but based on small cohorts of patients where this had already been confirmed clinically and no confounders were present. The use of CT angiography must only be used to support the best possible clinical diagnosis of death using neurological criteria and never to fully replace it. The use of CT angiography as an ancillary test to support the diagnosis of death using neurological criteria should follow a clear protocol and be interpreted by a consultant radiologist, with neuroradiology consultant involvement. We do not believe that routine CT angiography is indicated in isolated infratentorial brain pathology as it will only demonstrate absent brain blood flow once co-existing supratentorial injury develops (no longer isolated infratentorial brain pathology). Whilst isolated infratentorial brain pathology is present in 9% of UK deaths diagnosed using neurological criteria diagnoses [7], isolated brainstem pathology is extremely rare. More commonly isolated infratentorial brain pathology involves other posterior fossa structures and we suggest the diagnosis is delayed for at least 24 h after the loss of the last observed brainstem reflex.

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