Variability across countries for brain death determination in adults

ABSTRACT Background The guidelines of brain death determination vary across countries. Our aim was to compare diagnostic procedures of brain death determination in adults among five countries. Method Consecutive comatose patients who received brain death determination from June 2018 to June 2020 were included. The technical specifications, completion rates and positive rates of brain death determination according to criteria of different countries were compared. The accuracy, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of each ancillary test for the identification of brain death diagnosed according to different criteria were investigated. Results One hundred and ninety nine patients were included in this study. One hundred and thirty one (65.8%) patients were diagnosed with brain death according to French criteria, 132 (66.3%) according to Chinese criteria, and 135 (67.7%) according to criteria of USA, UK and Germany. The sensitivity and PPV of electroencephalogram (92.2% – 92.3%) and somatosensory evoked potential (95.5% – 98.5%) were higher than transcranial Doppler (84.3% – 86.0%). Conclusions The criteria of brain death in China and France are comparatively stricter than in USA, UK and Germany. The discrepancy in brain death determination between clinical assessments and additional confirmation of ancillary tests is small.


Introduction
The concept of death has been a philosophical debate as well as a medical controversy for millennia. The rapid development of technology in life support continues to blur the line between life and death. A major confusion among the public is the difference between death of the person and death of the human organs. In 1968, the Harvard Ad Hoc Committee proposed that death of the individual could be determined as the cessation of brain function (irreversible coma), despite the persistent respiration and circulation supported by mechanical ventilation (1). This visionary widely accepted concept opened up the avenue for exploring criteria and tools for brain death determination.
Most countries have implemented laws giving a legal definition of brain death; however, the legalization of brain death is still on the way in China (2). Medical consensuses have been reached across countries that the determination of brain death is to diagnose the irreversible cessation of the entire brain function by confirming the absence of consciousness due to a known cause, brainstem reflexes and spontaneous breathing. Only in the UK, brain death was defined as the irreversible cessation of brain-stem function (3,4). On the operational level, there are still a few disparities in the diagnostic procedures across countries. In this study, we compared national guidelines of brain death in adults among five countries with different criteria: China, UK, USA, France and Germany.

Study design
This retrospective study is based on a prospective database of consecutive comatose patients who received brain death determination in the Second Affiliated Hospital of Guangzhou University of Chinese Medicine, China. This study was approved by the Ethics Committee of The Second Affiliated Hospital of Guangzhou University of Chinese Medicine. All the procedures in brain death determination were based on the Chinese guidelines (5,6),;the informed consent was therefore waived. All the data in this study have been de-identified. This study was conducted in compliance with Chinese laws and the Declaration of Helsinki.

Brain death determination
Based on Chinese guidelines for the diagnosis and confirmation of brain death in adults (5,6), the determination of brain death contains three steps. The first step is the determination of testing prerequisites which includes: (1) the confirmation of a known cause for coma; (2) the exclusion of any reversible coma. The second step is the clinical assessment which includes three parts: (1) deep coma (GCS 2 T; all the stimuli should be given above the neck); (2) absence of brainstem reflexes including direct and indirect pupillary light reflexes, corneal reflex, oculocephalic reflex, oculovestibular reflex (using iced saline), and cough reflex; (3) apnea test. All these five reflexes should be absent after multiple repetitions. The third step is the confirmatory examinations consisting of electroencephalogram (EEG), short-latency somatosensory evoked potential (SLSEP), and transcranial Doppler (TCD). Two of the three confirmatory tests should be fulfilled. If any of the above brainstem reflexes cannot be tested, all the three confirmatory tests should be fulfilled. Apnea test was conducted after the fulfillment of all the other assessments in order to avoid any potential adverse event. All the assessments were conducted by neurologists with more than five years of clinical experience and with a certificate in national standard training of brain death determination. All the evaluations for one patient were given independently by two neurologists, and consensuses should be reached. For patients who admitted to our hospital before May 2019, the brain death determination was conducted according to Chinese guidelines in 2013 (5): brain death determination should be conducted twice at least 12 h apart, only the patients who fulfilled both sets of examinations can be diagnosed as brain death. For patients who admitted to our hospital after May 2019, the brain death determination was conducted according to Chinese guidelines in 2019 (6): brain death can be diagnosed after fulfilling one set of brain death determination tests.

Diagnostic standards of confirmatory tests
A continuous EEG is conducted for more than 30 min with eight scalp electrodes arranged according to the international 10-20 system (Fp1, Fp2, C3, C4, O1, O2, T3 and T4, referred to A1 and A2). The complete electrocerebral silence is defined as EEG activity ≤ 2 μV and is considered as brain death. SLSEP includes the following obligate components: N9, N13, P14, N18 and N20. Electrical stimulation was given at a rate of 1-5 Hz, with a pulse width of 0.1-0.2 ms (up to 0.5 ms, if necessary) and an intensity of 5-25 mA. Brain death in SLSEP is defined as the existence of bilateral N9 and/or N13 and the absence of bilateral P14, N18, and N20. Bilateral middle cerebral arteries are used to assess anterior circulation (alternative arteries: bilateral terminal internal carotid arteries or carotid siphons), and basilar artery for posterior circulation (alternative arteries: bilateral intracranial vertebral arteries). TCD should be performed twice at intervals of ≥ 30 min. Brain death in TCD is defined as the cerebral circulatory arrest presented with the following presence of the following flow patterns: reverberating flow, small systolic peaks in early systole and disappearance of flow signals.

Statistical analysis
Demographics, etiology, history of cardiopulmonary resuscitation (CPR) before brain death evaluation, use of vasopressors and continuous renal replacement therapy (CRRT) before or during brain death evaluation, and results of all the tests of brain death determination were collected for analysis. The positive rates between three confirmatory tests (EEG, SLSEP and TCD) were compared in pairs using Chi-square tests. The Chinese criteria of brain death were compared with national criteria of US (7), UK (3), Germany (8) and France (9). The accuracy, sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of each ancillary test for the identification of brain death confirmed according to different criteria were calculated. All the statistical analyses were performed with SPSS version 22 software (SPSS Inc., Chicago, IL, USA).

Clinical profiles
From June 2018 to June 2020, a total of 199 patients received brain death evaluations in our hospital ( Table 1). The median age was 44 years old, and the majority was male (81.9%). Intracranial hemorrhage (ICH), brain trauma and subarachnoid hemorrhage (SAH) were the most common etiologies in our cohort. Almost all the patients (97.5%) were given vasopressors to maintain blood pressure at a normal level, and more than half of patients (54.3%) received CRRT to maintain homeostasis.

Brain death determination
All the patients met testing prerequisites and did not have any brainstem reflexes (Table 2). Most patients received EEG and SLSEP, and less than half of patients were evaluated by TCD. The positive rates of EEG and SLSEP were significantly higher than TCD (EEG vs TCD: 96.4% vs 88.4%, p = 0.010; SLSEP vs TCD: 96.3% vs 88.4%, p = 0.011). The apnea test was not conducted in 44 patients who did not meet the prerequisites of apnea test and in eight patients died of cardiac arrest before the test. Apnea test was aborted in four patients due to arrhythmia or significant decrease of oxygen saturation, or blood  Table 2).

Comparisons of determination criteria among five countries
The general criteria of brain death determination in China, USA, UK, Germany and France were presented in Table 3.
Irreversible coma with a known etiology, absence of brainstem reflexes, and cessation of spontaneous respiration are mandatory in criteria of all the countries. The duration of apnea test is five minutes in British criteria, eight to ten minutes in American and Chinese criteria, and unspecified in German and French criteria. For patients who fulfil clinical criteria of brain death, confirmatory tests are not mandatory in USA, UK and Germany. Chinese criteria stipulate that two of the three confirmatory tests (EEG, TCD and SLSEP) must be fulfilled, and French criteria require at least one confirmatory test for the diagnosis of brain death. EEG is accepted in all five countries. Evoked potential test is accepted in China, UK, Germany, but were not recognized in US and France. To determine cerebral blood flow, TCD is accepted in China, UK, and Germany, but US and France recognize more advanced examinations, such as angiography ( Table 3). Examinations of cerebral metabolism are accepted in USA, UK and Germany, but are not mandatory. The diagnosis of brain death should be made by two independent raters in China, UK, Germany and France, whereas it is not specified in American guidelines.
China is the only country that organizes state certification for brain death diagnosis. Positive rates of each item of criteria of different countries were presented in Table 4. The results of apnea tests at 8 min were used in the determination of brain death based on criteria of these five countries, therefore the positive rate of apnea test might be slightly overestimated in UK criteria group. Among 199 patient who received brain death determination, 131 (65.8%) patients were diagnosed with brain death according to French criteria, 132 (66.3%) according to Chinese criteria, and 135 (67.7%) according to criteria of USA, UK and Germany. Among patients who could be diagnosed as brain death according to USA, UK, or German guidelines, three patients (2.2%, 3/135) could not be diagnosed as brain death in China, and four patients (3.0%, 4/135) could not be diagnosed in France ( Table 4).

Performance of confirmatory tests
Diagnostic performance of EEG, SLSEP, and TCD was analyzed for the identification of confirmed cases according to criteria of USA, France and China (Table 5). Among these three tests, EEG has the highest accuracy according to all the criteria (92.2%-92.3%). The sensitivity and PPV of EEG and SLSEP were higher than TCD, indicating that they can identify much more patients with brain death than TCD. All these three tests have a very low specificity and NPV, suggesting that only a small number of patients who are not brain dead can have the negative findings of confirmatory tests. This is mainly because some patients who cannot be diagnosed as brain death due to the failure of apnea test may present findings of brain death rather than normal finding on EEG, SLSEP or TCD.

Discussion
The determination of brain death is essential for medical decision making in comatose patients. However, how to determinate brain death accurately with appropriate tests has been an ethical and academical focus for long time. Currently, there are some disconformities across countries on the procedures of brain death determination. In this study, we summarized and compared the criteria of brain death in China, USA, UK, Germany and France, in order to help criteria and policiesmakers draw on the strengths of other countries' guidelines, take the consideration of each country's actual conditions, and develop better guidelines, regulations and polices of brain death.
Apnea test is a mandatory technique to confirm the absence of spontaneous respiration in criteria of all the countries. The positive result of apnea test is arterial P CO2 ≥ 60 mm Hg (or 20 mm Hg increase from the baseline level) and the absent respiratory movements (6,7). However, the duration of apnea test was not the same across countries. Short duration may lead to false negative, whereas long duration may induce  hypotension, severe hypoxemia and serious arrhythmia which cause secondary insults (10). The duration of apnea test is five minutes in UK, eight to ten minutes in USA and China, and unspecified in German and French criteria. Identifying the optimum duration of apnea test is a crucial issue that should be investigated in future studies. Moreover, apnea test with continuous positive airway pressure was proposed to be a safer method than the classic oxygen insufflation method (11)(12)(13). More related evidence may lead to revisions in criteria of brain death determination in the future. EEG is used to confirm the electrical inactivity of cortical layers in brain death determination. Very few studies investigated the validity of EEG in determination of brain death. A study in 1995 (n = 15) showed that EEG only had a sensitivity of 53% (14), and another study in 1987 (n = 56) reported a sensitivity of 80.6% (15). These two early studies compared the EEG with clinical criteria of brain death and used paper EEG recordings which might contain substantial artifacts. A recent German study (n = 67) and a Chinese study (n = 37) indicated that EEG had a high sensitivity of 94%-100% which was consistent with our findings (16,17).
Somatosensory evoked potentials (SEPs) test examines lemniscal pathways in the hemispheres and brainstem, and it was reported to be a reliable test for brain death determination with a sensitivity of 87.4%-100% (18)(19)(20). The examination of cerebral circulation provides an alternative evaluation of brain function. TCD is recognized as one of the three confirmatory tests in Chinese criteria of brain death. However, TCD is reported to a lower sensitivity (73%-78%) than EEG and SEPs (19,21). The diagnostic performance of ancillary tests may vary depending on the criteria of brain death in different countries, but our study suggests that such differences are small. Although we reported a higher sensitivity of 84.3%-86.0% for TCD, our finding that EEG and SEP have higher sensitivities than TCD is consistent with previous studies (19,21). Therefore, the results of EEG and SEP results should be given more weight than TCD, whether in China, USA, or Europe. Besides, TCD is limited by the penetrability of transtemporal windows and interexaminer variability. MR and CT angiography were proposed to assist brain death determination (22,23). However, angiography requires higher cost and the transfer of patients out of intensive care unit which generates potential safety hazards.
Among patients who had negative results of confirmatory tests (3 in EEG, 2 in SLSEP, and 8 in TCD), only 1 to 3 patients were not diagnosed as brain death according to guidelines in different countries. Therefore, the specificity and NPV of confirmatory tests were very low in our study. The positive results of confirmatory tests suggest a high likelihood of brain death, whereas the negative results do not necessarily mean that the brain is not dead. Among 135 (67.8%) patients who met the clinical criteria of brain death in our study, there were three patients who did not reach the brain death criteria of confirmatory tests, and they were not diagnosed as brain death in China. These three patients had no recovery of consciousness until the withdrawal of medical support. So far there are no  reports of neurologic function recovery in patients who met clinical diagnosis of brain death. The waiver of routine and mandatory use of ancillary tests may reduce the medical expenses, shorten the time for making the diagnosis of brain death, and increase the success rate of organ donation. However, the confirmation of ancillary tests can avoid potential human errors in clinical evaluations of brain death. Moreover, the raters of brain death should be trained and certified by national medical societies to minimize potential variability in the practice. There are some limitations in this study. Apnea tests were conducted for eight minutes in our patients according to Chinese criteria. Therefore, we are unable to investigate the positive rate and safety of different test durations. There is a possibility that the positive rate of apnea test was slightly overestimated, and the completion rate was mildly underestimated in patients evaluated according to UK criteria. Moreover, as EEG, SLSEP, and TCD are the only ancillary tests recognized in China, other ancillary tests, such as angiography, bispectral index, and positron emission tomography, were not conducted and investigated in this study.
In conclusions, diagnostic procedures of brain death vary among countries. The criteria of brain death in China and France are comparatively stricter than in USA, UK, and Germany. The discrepancy in brain death determination between clinical assessments and additional confirmation of ancillary tests is small.

Disclosure statement
No potential conflict of interest was reported by the author(s).

Funding
This study was funded by "Double-First Class" and Innovative Teams Project of Guangdong University of Chinese Medicine [2021xk26];

Author contributions
Study concept and design: FY, LW, SW; data acquisition: HL, TP, WW; analysis and interpretation of data: LH, TP, WW; drafting of the manuscript: FY and SW; study supervision: LW, SW; critical revision: FY, LW, SW. All authors read and approved the final manuscript.

Ethical statements
The study was approved by the Ethics Committee of The Second Affiliated Hospital of Guangzhou University of Chinese Medicine (ZE2020-217-01). All the procedures in brain death determination were based on the Chinese guidelines, the informed consent was waived therefore. All the data in this study have been de-identified. This study was conducted in compliance with Chinese laws and the Declaration of Helsinki.

Data availability statement
By request to the corresponding author.