A survey of American neurologists about brain death: understanding the conceptual basis and diagnostic tests for brain death

doi:10.1186/2110-5820-2-4

Ann Intensive Care. 2012; 2: 4.

Published online 2012 February 17. doi: 10.1186/2110-5820-2-4

PMCID: PMC3310851

A survey of American neurologists about brain death: understanding the conceptual basis and diagnostic tests for brain death

Ari R Joffe,^1,² Natalie R Anton,¹ Jonathan P Duff,¹ and Allan deCaen¹

¹Stollery Children's Hospital and University of Alberta, Edmonton, Alberta, Canada

²The John Dossetor Health Ethics Center, University of Alberta, Edmonton, Alberta, Canada

Corresponding author.

Ari R Joffe: ari.joffe/at/albertahealthservices.ca; Natalie R Anton: Natalie.anton/at/albertahealthservices.ca; Jonathan P Duff: Jon.duff/at/albertahealthservices.ca; Allan deCaen: allan.decaen/at/albertahealthservices.ca

Received August 5, 2011; Accepted February 17, 2012.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This article has been cited by other articles in PMC.

Abstract

Background

Neurologists often diagnose brain death (BD) and explain BD to families in the intensive care unit. This study was designed to determine whether neurologists agree with the standard concept of death (irreversible loss of integrative unity of the organism) and understand the state of the brain when BD is diagnosed.

Methods

A previously validated survey was mailed to a random sample of 500 board-certified neurologists in the United States. Main outcomes were: responses indicating the concept of death that BD fulfills and the empirical state of the brain that would rule out BD.

Results

After the second mailing, 218 (44%) surveys were returned. Few (n = 52, 27%; 95% confidence interval (CI), 21%, 34%) responded that BD is death because the organism has lost integrative unity. The most common justification was a higher brain concept (n = 93, 48%; 95% CI, 41%, 55%), suggesting that irreversible loss of consciousness is death. Contrary to the recent President's Council on Bioethics, few (n = 22, 12%; 95% CI, 8%, 17%) responded that the irreversible lack of vital work of an organism is a concept of death that the BD criterion may satisfy. Many responded that certain brain functions remaining are not compatible with a diagnosis of BD, including EEG activity, evoked potential activity, and hypothalamic neuroendocrine function. Many also responded that brain blood flow and lack of brainstem destruction are not compatible with a diagnosis of BD.

Conclusions

American neurologists do not have a consistent rationale for accepting BD as death, nor a clear understanding of diagnostic tests for BD.

Background

There are two ways to diagnose death: irreversible loss of circulation, and irreversible loss of all functions of the brain, including the brainstem [1]. Each is a criterion for death, because it marks the univocal state of death, the irreversible loss of the function of the organism as a whole. Integrative unity of the organism, including resistance of entropy and maintenance of internal homeostasis, is lost, leaving a mere collection of tissues and organs [1-4]. For medicine, law, and ethics, this is the written standard rationale for accepting brain death (BD) as a criterion for death [1-4]. The tests used at the bedside to diagnose BD verify the irreversible loss of all functions of the brain. Neurologists in the intensive care unit confirm BD by using a clinical neurologic examination, and once diagnosed the patient is dead; this diagnosis is "final and cannot be reversed. The person will never awaken [5]." Some authors have challenged this paradigm [3,4,6]. In response, neurologist groups have made it clear that BD conforms with the law as written in the Uniform Determination of Death Act (UDDA), with "accepted medical standards" [7-11] and that "it will be hard to find a physician closely involved with BD determination and organ donation who does not think those [BD patients] are dead [9]."

We designed a survey to determine whether board-certified neurologists in the United States agree with the standard concept of death (defined by the President's Commission and neurologist groups as the irreversible loss of integrative unity of the organism [1-4,6,10,11]), and understand the criterion of death (irreversible loss of all functions of the brain, including the brainstem), and the empirical state of the brain diagnosed by the tests used to confirm BD. We hypothesized that neurologists would not be aware of the standard paradigm justifying the diagnosis of death and would not understand the empirical state of patients determined dead based on the criterion of BD. This is important because the American Academy of Neurology suggests that neurologists have special expertise in declarations of BD [7,8].

Methods

Questionnaire administration

This study was a prospective survey of a random sampling of board-certified neurologists in the United States regarding their opinions about BD. The mailing list was obtained from Healthcare Lists Division SDI (Yardley, PA) in August 2009. Each neurologist was mailed the survey in January 2010, along with a $5 gift certificate to encourage them to have a coffee while filling out the questionnaire. A cover letter asked participants to complete the survey and mail it back in the addressed, stamped envelope. A second mailing was done in May 2010 to nonresponders. All responses were received by July 2010. The cover letter stated, "We are sending you a short questionnaire asking your opinions around some of the concepts surrounding BD. We want to sample the opinions regarding the concept of BD. Your responses are voluntary and confidential." The study was approved by our university health ethics research board.

Questionnaire development

The development and initial testing of the instrument are described in more detail elsewhere [12,13]. The current instrument (Additional File 1) is identical to that used in a survey of Canadian pediatric intensivists and Canadian neurosurgeons, with the following changes: (a) in the first question about acceptable conceptual reasons to explain BD, we added the choice "cessation of the vital work of a living organism--the work of self preservation, achieved through the organism's need driven commerce with the surrounding world" as stated by the President's Council; and (b) we modified the scenario regarding family refusal to stop "life support" in a brain-dead patient to describe continued support for 8 months until ventilator withdrawal, and asked "was this patient dead for the last 8 months?" and if the patient, during the last 8 months, was doing any of the three vital activities stated by the President's Council to indicate life (Additional File 1) [14].

To generate the items for inclusion in the questionnaire, we searched MEDLINE from 1996 to 2004 for articles on BD, followed by review of the relevant article reference lists. The new questions described above were based on the President's Council White Paper [14]. To ensure clarity, realism, validity, and ease of completion, initial pilot testing was done by having five local pediatric intensivists, one local pediatrician, and one local organ donation coordinator complete the questionnaire, followed by a semistructured interview for feedback.

Statistical analysis

Certain definitions were made a priori for two of the survey questions. The first question asked the respondent to choose from a list of "stand-alone" reason(s) that "is/are an acceptable conceptual reason to explain why 'brain death' is equivalent to 'death'." The seventh question asked, "This patient fulfills all brain death criteria unequivocally, including the suitable interval. Conceptually, why are they dead (i.e., in your own words, what is it about loss of brain function, including the brainstem, that makes this patient dead)?" For analysis, we classified responses into categories that have been discussed in the literature, including loss of integration concept of BD, higher brain concept of BD, prognosis concept of BD, and statement of the criterion only.

Anonymous data were entered into REDCap Survey (Version 1.3.9-^©2010 Vanderbilt University) and uploaded to the Statistical Package for the Social Sciences (SPSS, Inc., Chicago, IL) version 15.0 for Windows. We analyzed responses using standard descriptive tabulations and give adjusted Wald 95% confidence intervals (95% CI).

Results

The questionnaire was mailed to a random sample of 500 board-certified neurologists in the United States; after the second mailing, 218 (44%) had been returned. Of the 218 returned, 26 (12%) did not have data that could be analyzed: 24 were returned to sender, and 2 were returned blank. Therefore, there were 192 of 477 (40.3%) eligible surveys returned with data for analysis.

The first question asked, "Which of several choices is an acceptable stand-alone conceptual reason to explain why BD is equivalent to death." Fifty-two (27%; 95% CI, 21-34%) chose the irreversible loss of the integration of body functions by the brain, 22 (12%; 8-17%) a cessation of the vital work of the organism, and almost half (48%; 41-55%) used a higher brain concept (Table (Table11).

Table 1

Responses to the question on conceptual reasons to explain why brain death is equivalent to death

The next two questions asked about which objective test results, or pathology results (in a patient maintained as BD for 48 hours), would not be compatible with BD. A majority of respondents were unaware of the findings their patients may have when diagnosed with BD (Table (Table22).

Table 2

The objective findings that respondents considered would not be compatible with brain death

The next three questions asked about the timing of BD in different patient situations. When faced with a patient who has EEG activity yet fulfills BD criteria, 26 (14%; 9-19%) consider the patient dead at the first BD examination, 72 (38%; 31-45%) at the second examination, and 90 (47%; 40-54%) only when the EEG became isoelectric 12 hours later. When faced with a pregnant patient with BD supported for 11 weeks until delivery, most agreed the patient was dead by the first (36, 19%; 14-25%) or second (119, 62%; 55-69%) examination. However, in this brain-dead pregnant patient, 36 (19%; 14-25%) answered that she was not actually dead until sometime later: 11 (6%; 3-10%) after delivery of the neonate, 19 (10%; 6-15%) after organs are recovered and the ventilator is stopped, and 6 (3%; 1-7%) at none of these times. When faced with a brain-dead patient who has no cerebral blood flow but a family who insists on continued life support for the next months, and asked "was this patient dead for the last 8 months," 31 (16%; 12-22%) responded "no." When asked if this patient was performing vital work during those months, 164 (85%; 80-90%) responded no, and 30 (15%; 11-21%) responded yes [receptive to stimuli, 9 (5%; 2-9%); acting upon the world, 5 (3%; 1-6%), and carrying out basic (non-conscious) felt needs, 16 (8%; 5-13%)].

The next two questions asked again about the underlying conceptual basis of BD: "In your own words, what is it about loss of brain function including the brainstem that makes this patient dead?" and "Prior to this survey, had you thought about why, at a conceptual level, brain death is equivalent to death of the patient?" Only 21 (11%; 7-16%) of respondents had not previously thought about why BD is equivalent to death. In their own words, only 15 (8%; 5-13%) used a loss of integration concept (Table (Table33).

Table 3

Response to the question about what, in the respondent's own words, makes a patient dead

The next question asked which choice "best describes why you are comfortable diagnosing death based on the criteria of brain death?" Most (133, 69%; 62-75%) responded that "the conceptual basis of brain death makes it equivalent to death of the patient." Many responded that the reason is because it is a standard: an accepted medical standard (46, 24%; 18-30%), an accepted legal standard (24, 13%; 8-18%), and/or "the diagnosis of brain death was taught to me during my training" (14, 7%; 4-12%). Five (3%; 1-6%) were not comfortable diagnosing death based on BD.

The final question asked: "Are brain death and cardiac death the same state (i.e., are both death of the patient)?" More than half (104, 54%; 47-61%) chose "no," 86 (45%; 38-52%) chose "yes," and 2 (1%; 0-4%) left the answer blank.

Further analysis was done for those 133 (69%) who responded that they were comfortable diagnosing BD, because "the conceptual basis of brain death makes it equivalent to death of the patient." Their responses to the question asking to state the concept of BD in their own words is shown in Table Table3.3. Only 13 (10%; 6-16%) used a loss of integration concept, and 59 (44%; 36-53%) did not articulate a concept (i.e., used a restatement of the criterion or left no response). On the first question, only 39 (29%; 22-38%) considered "irreversible loss of the integration of body functions by the brain" as an acceptable conceptual reason to explain BD being equivalent to death and 67 (50%; 42-59%) chose a higher brain conceptual reason.

Discussion

The American Academy of Neurology recently updated their evidence-based guideline for determining BD in adults, reaffirming that irreversible cessation of all functions of the entire brain, including the brainstem, can be determined "based on straightforward principles," and is death [8]. This survey suggests that there are several potential flaws with this claim. First, most neurologists do not understand (at best) or disagree (at worst) with the standard concept that BD is death because the organism has lost integrative unity. The most common justification given by neurologists was a higher brain concept, suggesting that irreversible loss of consciousness is death. Very few neurologists consider the irreversible lack of vital work of an organism as a concept of death that the BD criterion may satisfy. Second, most neurologists do not understand (at best) or disagree (at worst) that certain brain functions, including EEG activity, evoked potential activity, and hypothalamic neuroendocrine function, often can remain in patients diagnosed dead using accepted tests that have confirmed the BD criterion [15]. This suggests that these neurologists think that clinical tests for BD produce many false-positive diagnoses of death. Third, most neurologists did not understand (at best) or disagree (at worst) that brain blood flow and lack of brain destruction often can occur in patients diagnosed dead using accepted tests confirming the BD criterion [15,16]. This suggests that there may be concern (or confusion) about whether BD marks the point of irreversible loss of brain functions. Finally, most neurologists do not consider the criterion BD and circulatory death as each diagnostic of the univocal state of death.

The concept of death

BD is said to be death by most professional bodies because it satisfies the concept/definition of death (Table (Table4):4): loss of integrative unity of the organism as a whole, marking when an organism is no longer an organism because it no longer can resist the forces of entropy and no longer can maintain internal homeostasis [1-4]. Many have argued that integrative unity of the organism as a whole often continues during BD (hence, integration is not dependent on functions of the brain), and a central integrator is not required for life; therefore, many no longer consider this a concept of death that BD satisfies [3,6,14]. Loss of personhood, based on irreversible loss of consciousness (sentience, or agency) is necessary, but not sufficient, for death (Table (Table4)4) [3,4]. Although nonconscious patients may be allowed to die due to their profound neurological disability, no society has accepted that they are already dead. It may be true that BD patients have poor quality of life or certainty of cardiac arrest in a short period; however, this denotes a prognosis and not a diagnosis of death. The President's Council suggested a novel concept of death: that vital external work of an organism is required to be alive, and once an organism no longer interacts with the environment to obtain what it needs to survive, it is dead [14]. Importantly, simply restating the criterion of BD does not give any concept of death that BD satisfies to justify BD being death.

Table 4

Conceptual and empirical arguments in favor of brain death, and problems with those arguments

This survey shows that neurologists do not understand if, or disagree whether, the criterion BD fulfils a concept of death. Few consider irreversible loss of integration of the organism as a whole or irreversible loss of the ability to perform external vital work as a reason to accept BD as death (some even consider that external work continues during BD). Many confused a restatement of the criterion of BD as justification that it is death, and a few conflated the prognosis of death with the diagnosis of death. Most consider a higher brain concept of death justified. This is concerning because neurologists often are the specialist declaring BD and explaining it to families in the intensive care unit.

The tests of BD

The tests for BD are performed to confirm that irreversible loss of all functions of the brain, including the brainstem, has occurred. It has been shown that some brain functions continue after accurately clinically diagnosed BD, including EEG activity in 20%, evoked potential activity in 5%, and hypothalamic neuroendocrine function in > 50% [15]. These activities may be explained by the finding that continued brain blood flow occurs in 5-40% of BD patients, and pathologic destruction of brain does not occur in more than 40% of BD patients (even after over 24-48 hr of maintained circulation) [15,16]. The ongoing brain functions have been explained with several controversial claims (Table (Table4)4) [3,4,15,17-19]. First, these are mere activities and not functions; however, the brain seems too complex an organ to simply make this claim [3,17]. Second, these are insignificant functions; however, this is an ad hoc claim [3,4,15,17]. Third, these are not critical clinical functions, and BD is a clinical diagnosis; however, this claim is both ad hoc and circular (critical clinical functions are necessary for maintenance of life, and death is the loss of critical clinical functions, is a trivial tautologous statement) [3,17]. Fourth, these are not critical functions, because they are replaceable mechanically; however, this would only lead to a higher brain consciousness based concept of death [3,4,15,17-19].

This survey shows that most neurologists do not understand, or disagree, that certain brain functions can remain in patients diagnosed dead using accepted clinical tests confirming the BD criterion. This may suggest that the accepted medical standard of clinical tests for BD can produce false-positive diagnoses of death. At the very least, the neurologists often are unaware of (or worse, disagree with) the debates regarding the meaning of significant, critical, clinical, brain functions.

Other potential interpretations

First, we assumed that there is a "standard concept of death." However, we included in the survey all the concepts offered in the literature and also provided an opportunity to provide a new concept in the open-ended question. Although we found that most neurologists did not agree with the concept of loss of integrative unity, the main alternative was a higher brain concept. This would imply that patients with permanent vegetative state are dead in their state of wakefulness and breathing. Second, perhaps the finding that 97% of neurologists are comfortable diagnosing death based on BD only shows that neurologists are not able to justify explicitly why the equivalency truly holds. After all, this is a philosophical question and may not involve terminology used in clinical training. Perhaps the main finding of the survey is uncovering an unmet neurologists' educational need. Although a potential interpretation, this may not be reassuring to families who are told that their loved one is dead based on the criterion BD. In addition, the American Board of Psychiatry and Neurology lists an understanding of BD on the objectives of training [20]. Third, although the survey did not determine this, perhaps neurologists accept BD as "dead enough" for organ donation and withdrawal of life-support purposes. Accordingly, patients with BD should be allowed to die or should be treated as if they no longer are part of the human moral community; but, this is different than being biologically dead. We agree with other authors who have suggested that if BD is not death, whether BD can be considered a state where vital organ donation complies with nonmaleficence (death is an unavoidable and minimal harm) and autonomy (with informed consent) requires further discussion and debate [21].

Limitations and strengths

The relatively small sample size, only modest response rate to this survey, and lack of information regarding respondents' exposure to BD patients are significant limitations. In addition, the closed-ended questions may not have allowed respondents to elaborate and clarify their responses. The strengths of the survey include the development methodology, and unambiguous nature of most of the questions. In addition, the striking similarity of our results to those of other surveys done in the past, including using this same survey in different populations of North American nonneurologist medical specialists, enhances the generalizability of the results [12,13,22-24]. The preponderance of evidence from this survey, and other surveys, support the conclusions we have drawn.

Conclusions

Neurologists do not have a consistent rationale for accepting BD as death, nor a clear understanding of the diagnostic tests for BD. Almost half accept BD because it is a state of permanent unconsciousness, and more than half do not consider it equivalent to circulatory death. Wijdicks, in explaining that BD is a clinical diagnosis, and that confirmatory tests are not needed, asks "So, what are neurologists confirming?" [25]. Unfortunately, he does not answer this question, and only claims that "confirmatory tests do not confirm anything [because BD] is synonymous with a certain clinical state [from which] there are no recoveries on record.... [25]" Similarly, the American Academy of Neurology and the Canadian Forum Brain Death Guidelines suggest that BD is death because of its prognosis (claiming it is irreversible) and lack of consciousness [7,8,26]. If BD is death, a conceptual rationale for this should be clarified. This has important ethical implications for the practice of intensive care medicine.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

ARJ designed the study, analyzed the data, and drafted the manuscript. All authors (ARJ, NRA, JPD, ARD) contributed to study conception and design, acquisition of data, interpretation of data, revised the manuscript critically for important intellectual content, and have given final approval of the version to be published.

Supplementary Material

Additional file 1

Brain Death Survey. The survey sent out to American neurologists asking for their opinions regarding brain death.

Click here for file^{(41K, DOC)}

Acknowledgements

There was no source of funding for this project. AJ had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Preliminary results of this study were presented as a poster at the American Thoracic Society conference, Denver, Colorado, USA, in May 2011.

References

President's Commission for the Study of Ethical Problems in Medicine and Biomedical and Behavioral Research. Defining Death: Medical, Legal and Ethical Issues in the Determination of Death. Washington, DC: U.S. Government Printing Office; 1981.
Bernat JL, Culver CM, Gert B. On the definition and criterion of death. Ann Intern Med. 1981;94:389–394. doi: 10.1001/archinte.94.3.389. [PubMed] [Cross Ref]
Nair-Collins M. Death, brain death, and the limits of science: why the whole-brain concept of death is a flawed public policy. J Law Med Ethics. 2010;38:667–683. doi: 10.1111/j.1748-720X.2010.00520.x. [PubMed] [Cross Ref]
Joffe AR. The neurological determination of death: what does it really mean? Issues Law Med. 2007;23:119–140. [PubMed]
American Academy of Neurology. AAN Summary of evidence-based guideline for caregivers and families of patients: determining brain death in adults. 2010. http://www.aan.com/practice/guideline/uploads/435.pdf (accessed 20 April 2011)
Shewmon DA. The brain and somatic integration: insights into the standard biological rationale for equating brain death with death. J Med Phil. 2001;26:457–478. doi: 10.1076/jmep.26.5.457.3000. [PubMed] [Cross Ref]
Report of the Quality Standards Subcommittee of the American Academy of Neurology. Practice parameters for determining brain death in adults (summary statement) Neurology. 1995;45:1012–1014. [PubMed]
Wijdicks EFM, Varelas PN, Gronseth GS, Greer DM. Evidence-based guideline update: determining brain death in adults. Report of the quality standards subcommittee of the American Academy of Neurology. Neurology. 2010;74:1911–1918. doi: 10.1212/WNL.0b013e3181e242a8. [PubMed] [Cross Ref]
de Groot YJ, Bakker J, Wijdicks EFM, Kompanje EJO. Imminent brain death and brain death are not the same: reply to Verheijde and Rady. Intensive Care Med. 2011;37:174. doi: 10.1007/s00134-010-2035-x. [PMC free article] [PubMed] [Cross Ref]
Bernat JL. The whole-brain concept of death remains optimum public policy. J Law Med Ethics. 2006;34:35–43. doi: 10.1111/j.1748-720X.2006.00006.x. [PubMed] [Cross Ref]
Battro A, Bernat JL, Bousser MG, Why the concept of brain death is valid as a definition of death. Vatican City: Pontificia Academia Scientiarvm; 2009. pp. 5–20. www.vatican.va/roman_curia/pontifical_academies/acdscien/2009/excerpt_signs_of_death_5l.pdf (accessed 20 April 2011)
Joffe AR, Anton N. Brain death: understanding of the conceptual basis by pediatric intensivists in Canada. Arch Pediatr Adolesc Med. 2006;160:747–752. doi: 10.1001/archpedi.160.7.747. [PubMed] [Cross Ref]
Joffe AR, Anton N, Mehta V. A survey to determine the understanding of the conceptual basis and diagnostic tests used for brain death by neurosurgeons in Canada. Neurosurgery. 2007;61:1039–1047. doi: 10.1227/01.neu.0000303200.84994.ae. [PubMed] [Cross Ref]
President's Council of Bioethics. Controversies in the Determination of Death. Washington, D.C.: President's Council of Bioethics; 2008. http://bioethics.georgetown.edu/pcbe/reports/death/Controversies%20in%20the%20Determination%20of%20Death%20for%20the%20Web%20(2).pdf (accessed 20 April 2011)
Joffe AR. Are recent defenses of the brain death concept adequate? Bioethics. 2010;24:47–53. doi: 10.1111/j.1467-8519.2008.00709.x. [PubMed] [Cross Ref]
Wijdicks EFM, Pfeifer EA. Neuropathology of brain death in the modern transplant era. Neurology. 2008;70:1234–1237. doi: 10.1212/01.wnl.0000289762.50376.b6. [PubMed] [Cross Ref]
Collins M. Reevaluating the dead donor rule. J Med Philos. 2010;35:154–179. doi: 10.1093/jmp/jhq009. [PubMed] [Cross Ref]
Joffe AR. The ethics of donation and transplantation: are definitions of death being distorted for organ transplantation? Phil Ethics Humanities Med. 2007;2:28. doi: 10.1186/1747-5341-2-28. (1-7) [PMC free article] [PubMed] [Cross Ref]
Thomas AG. Continuing the definition of death debate: the report of the President's Council on Bioethics on controversies in the determination of death. Bioethics. in press . [PubMed]
American Board of Psychiatry & Neurology: Neurology Core Competencies Outline. http://www.abpn.com/downloads/core_comp_outlines/2011_core_N_MREE.pdf (accessed December 8, 2011)
Miller FG, Truog RD. Rethinking the ethics of vital organ donations. Hastings Cent Rep. 2008;38:38–46. [PubMed]
Youngner SJ, Landefeld CS, Coulton CJ, Juknialis BW, Leary M. 'Brain death' and organ retrieval. A cross-sectional survey of knowledge and concepts among health professionals. JAMA. 1989;261:2205–2210. doi: 10.1001/jama.1989.03420150055037. [PubMed] [Cross Ref]
Lock M. Inventing a new death and making it believable. Anthropol Med. 2002;9:97–115. doi: 10.1080/1364847022000029705. [Cross Ref]
Tomlinson T. Misunderstanding death on a respirator. Bioethics. 1990;4:253–264. doi: 10.1111/j.1467-8519.1990.tb00088.x. [PubMed] [Cross Ref]
Wijdicks EFM. The case against confirmatory tests for determining brain death in adults. Neurology. 2010;75:77–83. doi: 10.1212/WNL.0b013e3181e62194. [PubMed] [Cross Ref]
Shemie SD, Doig C, Dickens B. et al. Severe brain injury to neurological determination of death: Canadian forum recommendations. CMAJ. 2006;174(Suppl):S1–S12. [PMC free article] [PubMed]

Articles from Annals of Intensive Care are provided here courtesy of
Springer-Verlag