مرگ مغزی
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مرگ مغزی به وضعیت غیرقابل بازگشت همه عملکردهای مغز اطلاق می‌شود. درچنین وضعیتی همهٔ نورونهای مغز در نتیجهٔ هیپوکسی تخریب می‌شوند. مرگ مغزی یکی از معیارهای قطعی تعیین‌کننده مرگ است. (معیار دیگر از بین‌رفتن گردش خون و تنفس است) برای تشخیص مرگ مغزی باید تمامی اعمال مغزی به صورت غیرقابل‌برگشت از بین رفته‌باشند. مرگ مغزی به‌طور واضح با حالت زندگی نباتی متفاوت است. در حالت مرگ مغزی تمام قسمت‌های مغز از جمله ساقه مغز از بین رفته‌است و تنفس بدون دستگاه تنفس مصنوعی وجود ندارد. این در حالی است که در حالت زندگی نباتی فرد بدون دستگاه دارای تنفس خودبخودی است. دلایل مرگ مغزی[ویرایش]تصادفات رانندگی، وارد آمدن ضربه شدید به سر، سقوط از ارتفاع، خونریزی‌های داخلی مغز، سکته مغزی و مسمومیت‌های شدید از علل مهم مرگ مغزی به‌شمار می‌روند.[۱] معیارهای مرگ مغزی[ویرایش]معیارهای فعلی برای تعیین مرگ مغزی عبارتنداز:
بیمار باید به تحریکات حسی شامل درد و کلام پاسخی نشان ندهد.
رفلکس‌های مردمک، قرنیه و حلقی دهانی باید از بین رفته باشند. رفلکس‌اکولوسفالیک و رفلکس اکولووستیبولار سبب حرکت چشم‌ها نمی‌شوند. فعالیت تنفسی وجود ندارند؛ که با رسیدن فشار دی‌اکسید کربن بیمار به ۶۰ میلی‌متر جیوه مشخص می‌شود به‌طوریکه با تجویز اکسیژن ۱۰۰ ٪ نیز فعالیت تنفسی وجود ندارد.
درالکتروانسفالوگرافی امواج الکتروآنسفالوگرام مغزی صاف است. تداوم اختلال عمل مغز معیارهای مرگ مغزی باید به مدت کافی ادامه یابند معمولاً با گذشت ۶ تا ۲۴ ساعت تشخیص، گذاشته می‌شود. برگشت‌پذیری اختلال عمل مغز علت اغما باید مشخص شود، تابلوی بالینی را توجیه کند و غیرقابل بازگشت باشد. مسمویت با داروهای آرام‌بخش، هیپوترمی، بلوک عصبی عضلانی و شوک باید رد شوند زیرا این اختلالات سبب بروز سندرم بالینی شبیه به مرگ مغزی می‌شوند که برگشت پذیرند. تفاوت‌های مرگ مغزی با کما[ویرایش]در حالت کما شانس بهبود برای برخی بیماران وجود دارد، در صورتی که در مرگ مغزی بهبود بیمار غیرممکن و مرگ وی ظرف چند روز حتمی است. کما یک نوع اختلال در کارکرد مغز بوده که در آن شخص ـ مشابه مرگ مغزی به دلیل کمبود خون و اکسیژن رسانی به مغز ـ دچار کاهش شدید سطح هوشیاری می‌شود و به هیچ‌یک از تحریکات پیرامونش پاسخ نمی‌دهد. در حالت کما شخص ممکن است برای مدت طولانی زنده بماند و زندگی نباتی پیدا کند و حتی افرادی که به کما رفته‌اند در صورت سالم بودن ساقه مغز، در اغلب موارد به تنفس غیرارادی خود ادامه داده و ضربان قلب منظمی نیز دارند. هوشیاری بیماران در حالت کما بسته به میزان پاسخ آن‌ها به محرک‌های گوناگون درجه‌بندی می‌شود. در جریان مرگ مغزی اعضای دیگر بدن مانند قلب، کلیه‌ها یا کبد تا مدتی زنده و قابل پیوند هستند و این ارگان‌ها درصورت اقدام بموقع می‌توانند در بدن شخص دیگری به وسیله پیوند اعضا استفاده شوند. با این حال، تخریب اعضای بدن به فاصله کمی پس از مرگ مغزی شروع می‌شود و به همین علت است که فرایند پیوند اعضا باید هرچه زودتر انجام شود.[۱] جستارهای وابسته[ویرایش]منابع[ویرایش]
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Brain death is the complete loss of brain function (including involuntary activity necessary to sustain life).[1][2][3][4] It differs from persistent vegetative state, in which the person is alive and some autonomic functions remain.[5] It is also distinct from an ordinary coma, whether induced medically or caused by injury and/or illness, even if it is very deep, as long as some brain and bodily activity and function remains; and it is also not the same as the condition known as locked-in syndrome. A differential diagnosis can medically distinguish these differing conditions. Brain death is used as an indicator of legal death in many jurisdictions, but it is defined inconsistently and often confused by the lay public.[6] Various parts of the brain may keep functioning when others do not anymore, and the term "brain death" has been used to refer to various combinations. For example, although one major medical dictionary[7] considers "brain death" to be synonymous with "cerebral death" (death of the cerebrum), the US National Library of Medicine Medical Subject Headings (MeSH) system defines brain death as including the brainstem. The distinctions are medically significant because, for example, in someone with a dead cerebrum but a living brainstem, spontaneous breathing may continue unaided, whereas in whole-brain death (which includes brainstem death), only life support equipment would maintain ventilation. Patients classified as brain-dead can have their organs surgically removed for organ donation. ContentsLegal historyTraditionally, both the legal and medical communities determined death through the permanent end of certain bodily functions in clinical death, especially respiration and heartbeat. With the increasing ability of the medical community to resuscitate people with no respiration, heartbeat, or other external signs of life, the need for another definition of death occurred, raising questions of legal death. This gained greater urgency with the widespread use of life support equipment, as well as rising capabilities and demand for organ transplantation. Since the 1960s, laws on determining death have, therefore, been implemented in all countries with active organ transplantation programs. The first European country to adopt brain death as a legal definition (or indicator) of death was Finland in 1971. In the United States, Kansas had enacted a similar law earlier.[8] An ad hoc committee at Harvard Medical School published a pivotal 1968 report to define irreversible coma.[9][10] The Harvard criteria gradually gained consensus toward what is now known as brain death. In the wake of the 1976 Karen Ann Quinlan case, state legislatures in the United States moved to accept brain death as an acceptable indication of death. In 1981 a Presidential commission issued a landmark report – Defining Death: Medical, Legal, and Ethical Issues in the Determination of Death [11] – that rejected the "higher brain" approach to death in favor of a "whole brain" definition. This report was the basis for the Uniform Determination of Death Act, which has been enacted in 39 states of the United States.[12] The Uniform Determination of Death Act in the United States attempts to standardize criteria. Today, both the legal and medical communities in the US use "brain death" as a legal definition of death, allowing a person to be declared legally dead even if life support equipment keeps the body's metabolic processes working.[13] In the UK, the Royal College of Physicians reported in 1995, abandoning the 1979 claim that the tests published in 1976 sufficed for the diagnosis of brain death and suggesting a new definition of death based on the irreversible loss of brain stem function alone.[14] This new definition, the irreversible loss of the capacity for consciousness and for spontaneous breathing, and the essentially unchanged 1976 tests held to establish that state, have been adopted as a basis of death certification for organ transplant purposes in subsequent Codes of Practice.[15][16] The Australia and New Zealand Intensive Care Society (ANZICS) states that the "determination of brain death requires that there is unresponsive coma, the absence of brain-stem reflexes and the absence of respiratory centre function, in the clinical setting in which these findings are irreversible. In particular, there must be definite clinical or neuro-imaging evidence of acute brain pathology (e.g. traumatic brain injury, intracranial haemorrhage, hypoxic encephalopathy) consistent with the irreversible loss of neurological function."[17] Medical criteriaNatural movements also known as the Lazarus sign or Lazarus reflex can occur on a brain-dead person whose organs have been kept functioning by life support. The living cells that can cause these movements are not living cells from the brain or brain stem; these cells come from the spinal cord. Sometimes these body movements can cause false hope for family members. A brain-dead individual has no clinical evidence of brain function upon physical examination. This includes no response to pain and no cranial nerve reflexes. Reflexes include pupillary response (fixed pupils), oculocephalic reflex, corneal reflex, no response to the caloric reflex test, and no spontaneous respirations. Brain death can sometimes be difficult to differentiate from other medical states such as barbiturate overdose, alcohol intoxication, sedative overdose, hypothermia, hypoglycemia, coma, and chronic vegetative states. Some comatose patients can recover to pre-coma or near pre-coma level of functioning, and some patients with severe irreversible neurological dysfunction will nonetheless retain some lower brain functions, such as spontaneous respiration, despite the losses of both cortex and brain stem functionality. Such is the case with anencephaly. Brain electrical activity can stop completely, or drop to such a low level as to be undetectable with most equipment. An EEG will therefore be flat, though this is sometimes also observed during deep anesthesia or cardiac arrest.[18] Although in the United States a flat EEG test is not required to certify death, it is considered to have confirmatory value. In the UK it is not considered to be of value because any continuing activity it might reveal in parts of the brain above the brain stem is held to be irrelevant to the diagnosis of death on the Code of Practice criteria.[19] The diagnosis of brain death is often required to be highly rigorous, in order to be certain that the condition is irreversible. Legal criteria vary, but in general require neurological examinations by two independent physicians. The exams must show complete and irreversible absence of brain function (brain stem function in UK),[20] and may include two isoelectric (flat-line) EEGs 24 hours apart (less in other countries where it is accepted that if the cause of the dysfunction is a clear physical trauma there is no need to wait that long to establish irreversibility). The patient should have a normal temperature and be free of drugs that can suppress brain activity if the diagnosis is to be made on EEG criteria.  Radionuclide scan: No intracranial blood flow. The "hot-nose" sign is shown. Also, a radionuclide cerebral blood flow scan that shows complete absence of intracranial blood flow must be considered with other exams – temporary swelling of the brain, particularly within the first 72 hours, can lead to a false positive test on a patient that may recover with more time.[21] CT angiography is neither required nor sufficient test to make the diagnosis.[22] Confirmatory testing is only needed under the age of 1.[2] For children and adults, testing is optional. Other situations possibly requiring confirmatory testing include severe facial trauma where determination of brainstem reflexes will be difficult, pre-existing pupillary abnormalities, and patients with severe sleep apnea and/or pulmonary disease.[2] Confirmatory tests include: cerebral angiography, electroencephalography, transcranial Doppler ultrasonography, and cerebral scintigraphy (technetium Tc 99m exametazime). Cerebral angiography is considered the most sensitive confirmatory test in the determination of brain death.[2] Organ donationWhile the diagnosis of brain death has become accepted as a basis for the certification of death for legal purposes, it is a very different state from biological death - the state universally recognized and understood as death.[23] The continuing function of vital organs in the bodies of those diagnosed brain dead, if mechanical ventilation and other life-support measures are continued, provides optimal opportunities for their transplantation. When mechanical ventilation is used to support the body of a brain dead organ donor pending a transplant into an organ recipient, the donor's date of death is listed as the date that brain death was diagnosed.[24] In some countries (for instance, Spain,[25] Finland, Wales, Portugal, and France), everyone is automatically an organ donor after diagnosis of death on legally accepted criteria, although some jurisdictions (such as Singapore, Spain, Wales, France, Czech Republic, Poland and Portugal) allow opting out of the system. Elsewhere, consent from family members or next-of-kin may be required for organ donation. In New Zealand, Australia, the United Kingdom (excluding Wales) and most states in the United States, drivers are asked upon application if they wish to be registered as an organ donor.[26] In the United States, if the patient is at or near death, the hospital must notify a transplant organization of the person's details and maintain the patient while the patient is being evaluated for suitability as a donor.[27] The patient is kept on ventilator support until the organs have been surgically removed. If the patient has indicated in an advance health care directive that they do not wish to receive mechanical ventilation or has specified a do not resuscitate order and the patient has also indicated that they wish to donate their organs, some vital organs such as the heart and lungs may not be able to be recovered.[28] See alsoReferences
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