Intracranial pressure and cerebral perfusion pressure during apnoea testing for the diagnosis of brain death - an observational study

Loss of cerebral blood flow and cerebral perfusion pressure in brain death: A transcranial Duplex ultrasonography study

PURPOSE

We investigated cerebral perfusion pressure (CPP) at the time loss of cerebral blood flow (CBF) occurred during brain death (BD). We hypothesized that a critical closing pressure (CrCP) may be reached before CPP drops to 0 mmHg.

MATERIALS AND METHODS

14 patients with increasing intracranial pressure (ICP) leading to BD were included. Transcranial Duplex (TCD) ultrasonography was used to investigate CBF. Starting at a CPP of 30 mmHg, TCD was repeated until waveforms indicated loss of CBF. We then analyzed CPP by the time TCD indicated absent CBF and clinical BD was established.

RESULTS

In 12 patients, CPP was positive when clinical BD was manifest and TCD illustrated absent CBF. Across all patients, mean CPP at clinical BD manifestation was 10.0 mmHg (range 0-20 mmHg); mean CPP by the time CBF stopped was 7.5 mmHg (0-20 mmHg). In four patients, clinical BD preceded loss of CBF. Here, the mean CPP difference from clinical BD to loss of CBF was 8.8 mmHg (5-15 mmHg).

CONCLUSIONS

CrCP may be reached although CPP is still positive, resulting in complete loss of CBF and BD. By including bedside TCD, neuromonitoring may contribute to early identification of patients at risk to experience loss of CBF and subsequent BD.

Statement in Support of Revising the Uniform Determination of Death Act and in Opposition to a Proposed Revision

Discrepancies between the Uniform Determination of Death Act (UDDA) and the adult and pediatric diagnostic guidelines for brain death (BD) (the "Guidelines") have motivated proposals to revise the UDDA. A revision proposed by Lewis, Bonnie and Pope (the RUDDA), has received particular attention, the three novelties of which would be: (1) to specify the Guidelines as the legally recognized "medical standard," (2) to exclude hypothalamic function from the category of "brain function," and (3) to authorize physicians to conduct an apnea test without consent and even over a proxy's objection. One hundred seven experts in medicine, bioethics, philosophy, and law, spanning a wide variety of perspectives, have come together in agreement that while the UDDA needs revision, the RUDDA is not the way to do it. Specifically, (1) the Guidelines have a non-negligible risk of false-positive error, (2) hypothalamic function is more relevant to the organism as a whole than any brainstem reflex, and (3) the apnea test carries a risk of precipitating BD in a non-BD patient, provides no benefit to the patient, does not reliably accomplish its intended purpose, and is not even absolutely necessary for diagnosing BD according to the internal logic of the Guidelines; it should at the very least require informed consent, as do many procedures that are much more beneficial and less risky. Finally, objections to a neurologic criterion of death are not based only on religious belief or ignorance. People have a right to not have a concept of death that experts vigorously debate imposed upon them against their judgment and conscience; any revision of the UDDA should therefore contain an opt-out clause for those who accept only a circulatory-respiratory criterion.

Apnea Testing for the Determination of Brain Death: A Systematic Scoping Review

Apnea is one of the three cardinal findings in brain death (BD). Apnea testing (AT) is physiologically and practically complex. We sought to review described modifications of AT, safety and complication rates, monitoring techniques, performance of AT on extracorporeal membrane oxygenation (ECMO), and other relevant considerations regarding AT. We conducted a systematic scoping review to answer these questions by searching the literature on AT in English language available in PubMed or EMBASE since 1980. Pediatric or animal studies were excluded. A total of 87 articles matched our inclusion criteria and were qualitatively synthesized in this review. A large body of the literature on AT since its inception addresses a variety of modifications, monitoring techniques, complication rates, ways to perform AT on ECMO, and other considerations such as variability in protocols, lack of uniform awareness, and legal considerations. Only some modifications are widely used, especially methods to maintain oxygenation, and most are not standardized or endorsed by brain death guidelines. Future updates to AT protocols and strive for unification of such protocols are desirable.

Does the Uniform Determination of Death Act Need to Be Revised?

Prompted by concerns raised by the rise in litigations, which challenge the legal status of brain death (BD), Lewis and colleagues recently proposed a revision of the Uniform Determination of Death Act (UDDA). The revision consists of (i) narrowing down the definition of BD to the loss of specific brain functions, namely those functions that can be assessed on bedside neurological examination; (ii) requiring that the determination of BD must be in accordance with the specific guidelines designated in the revision; and (iii) eliminating the necessity for obtaining consent prior to performing the tests for BD determination. By analyzing Lewis and colleagues' revision, this article shows that this revision is fraught with difficulties. Therefore, this article also proposes two approaches for an ethical revision of the UDDA; the first is in accordance with scientific realism and Christian anthropology, while the second is grounded in trust and respect for persons. If the UDDA is to be revised, then it should be based on sound ethical principles in order to resolve the ongoing BD controversies and rebuild public trust.

Summary

This article critically examines the recent revision of the Uniform Determination of Death Act (UDDA) advanced by Lewis and colleagues. The revision only further reinforces the status quo of brain death without taking into account the root cause of the litigations and controversies about the declaration of death by neurological criteria. In view of this deficiency, this article offers two approaches to revising the UDDA, both of which are founded on sound moral principles.

[Diagnosis of irreversible loss of brain function ("brain death")-what is new?]

The determination of the irreversible cessation of brain function (ICBF) is conducted in Germany according to the guideline of the German Medical Association, which is currently its fourth update issued in July 2015. This article provides an assessment of the current situation including an international comparison. International case reports with allegedly incorrect ICBF diagnosis are reviewed from the point of view of the German guideline. These case reports underpin the validity of the German guideline, especially its following provisions: (1) in patients with known or suspected adaptation to chronic hypercapnia, apnea cannot be diagnosed as usual; therefore in such a case the proof of cerebral circulatory arrest is mandatory; (2) if perfusion scintigraphy is used for proof of cerebral circulatory arrest, only validated lipophilic radiopharmaceuticals are allowed. This is compatible with new research data which indicate that cellular function can be reactivated for several hours after circulatory arrest but not the brain function. The recently updated recommendations of the German Society for Clinical Neurophysiology and Functional Imaging (DGKN) for ancillary testing include editorial adaptations (e.g., the more precise specification of the electrode positions for electroencephalography), standards of display screen with digital electroencephalography and age-related minimum values of mean arterial pressure for Doppler and duplex sonography in children. The novel requirements regarding the institutional organization of ICBF diagnostics in Germany issued in the "Second law on the amendment of transplantation law-improvement of the cooperation and the framework for organ donation" that became effective recently are presented and discussed critically in this review.

Progress of intracranial pressure and cerebral perfusion pressure in patients during the development of brain death

BACKGROUND

Clinical investigations of brain death are supposed to prove absence of cerebral perfusion. However, only limited data are available documenting intracranial pressure (ICP) and cerebral perfusion pressure (CPP) during the development of brain death. Our study presents additional data to understand the course of ICP and CPP in patients developing brain death.

MATERIAL AND METHODS

We analyzed retrospective data of 18 patients with ICP monitoring during the development of brain death due to primary brain lesions. ICP and CPP values were continuously measured between two clinically defined time points: 1. non-reactive and widened pupils, 2. brain death determination. We analyzed ICP and CPP at the above-mentioned end points. Additionally, we investigated maximum ICP and minimal CPP values between these time points.

RESULTS

Patients developed fixed and dilated pupils with a median of 38 h before brain death determination. During brain death determination median ICP and median CPP were 103.5 and -2.5 mmHg, respectively. Maximum ICP before brain death determination was significantly higher and minimal CPP values were significantly lower compared to the time point of brain death. During the investigation period all patients experienced ICP values >95 mmHg and CPP < 10 mmHg. All but one patient had documented CPP values of ≤0 mmHg. This single patient had a minimum CPP of 8 mmHg with a maximum ICP of 145 mmHg.

CONCLUSION

Cerebral perfusion pressure during brain death determination may be positive in some patients. Our results showed variable values of ICP and CPP. However, extremely elevated ICP values before or during brain death in combination with low CPP values suggest absence of cerebral perfusion. The occurrence of positive CPP values during brain death determination therefore depends on the time point at which brain death determination is performed.

Medicolegal Complications of Apnoea Testing for Determination of Brain Death

Recently, there have been a number of lawsuits in the United States in which families objected to performance of apnoea testing for determination of brain death. The courts reached conflicting determinations in these cases. We discuss the medicolegal complications associated with apnoea testing that are highlighted by these cases and our position that the decision to perform apnoea testing should be made by clinicians, not families, judges, or juries.

Primary Posterior Fossa Lesions and Preserved Supratentorial Cerebral Blood Flow: Implications for Brain Death Determination

BACKGROUND

Patients with primary posterior fossa catastrophic lesions may clinically meet brain death criteria, but may retain supratentorial brain function or blood flow. These patients could be declared brain-dead in the United Kingdom (UK), but not in the United States of America (USA). We report the outcome of adult patients with primary posterior fossa lesions without concurrent major supratentorial injury.

METHODS

Henry Ford Hospital database was reviewed over a period of 88 months in order to identify all adult patients with isolated brainstem or posterior fossa lesions. We excluded patients with concurrent significant supratentorial pathology potentially confounding the clinical brain death examination. One more patient from a different hospital meeting these criteria was also included.

RESULTS

Three patients out of 161 met inclusion criteria (1.9% of all brain deaths during this period). With the addition of a fourth patient from another hospital, 4 patients were analyzed. All four patients had catastrophic brainstem and cerebellar injuries meeting the clinical criteria of brain death with positive apnea test in the UK. All had preserved supratentorial blood flow, which after a period of 2 h to 6 days disappeared on repeat testing, allowing declaration of brain death by US criteria in all four. One patient became an organ donor.

CONCLUSIONS

Patients with primary posterior fossa catastrophic lesions, who clinically seem to be brain-dead, evolve from retaining to losing supratentorial blood flow. If absent cerebral blood flow is used as an additional criterion for the declaration of death by neurological criteria, these patients are not different than those who become brain death due to supratentorial lesions.

Inconsistencies Between the Criterion and Tests for Brain Death

The whole-brain criterion of death provides that a person who has irreversibly lost all clinical functions of the brain is dead. Bedside brain death (BD) tests permit physicians to determine BD by showing that the whole-brain criterion of death has been fulfilled. In a nonsystematic literature review, we identified and analyzed case reports of a mismatch between the whole-brain criterion of death and bedside BD tests. We found examples of patients diagnosed as BD who showed (1) neurologic signs compatible with retained brain functions, (2) neurologic signs of uncertain origin, and (3) an inconsistency between standard BD tests and ancillary tests for BD. Two actions can resolve the mismatch between the whole-brain criterion of death and BD tests: (1) loosen the whole-brain criterion of death by requiring only the irreversible cessation of relevant brain functions and (2) tighten BD tests by requiring an ancillary test proving the cessation of intracranial blood flow. Because no one knows the precise brain functions whose loss is necessary to fulfill the whole-brain criterion of death, we advocate tightening BD tests by requiring the absence of intracranial blood flow.

Ethical and Legal Concerns With Nevada's Brain Death Amendments

In early 2017, Nevada amended its Uniform Determination of Death Act (UDDA), in order to clarify the neurologic criteria for the determination of death. The amendments stipulate that a determination of death is a clinical decision that does not require familial consent and that the appropriate standard for determining neurologic death is the American Academy of Neurology's (AAN) guidelines. Once a physician makes such a determination of death, the Nevada amendments require the withdrawal of life-sustaining treatment within twenty-four hours with limited exceptions. Neurologists have generally supported Nevada's amendments for clarifying the diagnostic standard and limiting the ability of family members to challenge it. However, it is more appropriate to view the Nevada amendments with concern. Even though the primary purpose of the UDDA is to ensure that all functions of a person's entire brain have ceased, the AAN guidelines do not accurately assess this. In addition, by characterizing the determination of death as solely a clinical decision, the Nevada legislature has improperly ignored the doctrine of informed consent, as well as the beliefs of particular faiths and cultures that reject brain death. Rather than resolving controversies regarding brain death determinations, the Nevada amendments may instead instigate numerous constitutional challenges.

Brain death after decompressive craniectomy: Incidence and pathophysiological mechanisms

PURPOSE

Patients who received decompressive craniectomy (DC) are usually not regarded to qualify for brain death (BD) as intracranial pressure (ICP) is not assumed to reach levels critical enough to cause cerebral perfusion failure. Here we investigated the incidence of BD after DC and analyzed the pathophysiological mechanisms.

MATERIALS AND METHODS

We searched our chart records of patients with DC for individuals who developed BD (2010-2016). We then analyzed the course of ICP and cerebral perfusion pressure (CPP) prior to BD and results from radiological tests that aim at demonstrating loss of cerebral perfusion in BD.

RESULTS

BD was diagnosed in 12 of 164 (incidence 7.3%) patients (age=16-70years; male=7; mean longitudinal diameter: 136.2mm). Mean latency between DC and BD was 69.4h. Immediately after DC, mean ICP was 30.0mmHg (standard deviation±24.7mmHg), CPP was 56.8mmHg (±28.1). In the course to BD, ICP increased to 95.8mmHg (±16.1), CPP decreased to -9.9mmHg (±11.2). In patients in whom radiological methods were performed (n=5) loss of cerebral perfusion was demonstrated.

CONCLUSIONS

Our study evidences that DC does not exclude BD. Even after DC, BD is preceded by a severely reduced CPP, supporting loss of cerebral perfusion as a critical step in BD pathophysiology.

Intracranial pressure and cerebral perfusion pressure in patients developing brain death

PURPOSE

We investigated whether a critical rise of intracranial pressure (ICP) leading to a loss of cerebral perfusion pressure (CPP) could serve as a surrogate marker of brain death (BD).

MATERIALS AND METHODS

We retrospectively analyzed ICP and CPP of patients in whom BD was diagnosed (n = 32, 16-79 years). Intracranial pressure and CPP were recorded using parenchymal (n = 27) and ventricular probes (n = 5). Data were analyzed from admission until BD was diagnosed.

RESULTS

Intracranial pressure was severely elevated (mean ± SD, 95.5 ± 9.8 mm Hg) in all patients when BD was diagnosed. In 28 patients, CPP was negative at the time of diagnosis (-8.2 ± 6.5 mm Hg). In 4 patients (12.5%), CPP was reduced but not negative. In these patients, minimal CPP was 4 to 18 mm Hg. In 1 patient, loss of CPP occurred 4 hours before apnea completed the BD syndrome.

CONCLUSIONS

Brain death was universally preceded by a severe reduction of CPP, supporting loss of cerebral perfusion as a critical step in BD development. Our data show that a negative CPP is neither sufficient nor a prerequisite to diagnose BD. In BD cases with positive CPP, we speculate that arterial blood pressure dropped below a critical closing pressure, thereby causing cessation of cerebral blood flow.