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Clinical death is the
medical term Medical terminology is a language used to precisely describe the human body including all its components, processes, conditions affecting it, and procedures performed upon it. Medical terminology is used in the field of medicine Medical terminolog ...
for cessation of
blood circulation The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
and breathing, the two criteria necessary to sustain the lives of human beings and of many other organisms. It occurs when the
heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...
stops beating in a regular rhythm, a condition called
cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possib ...
. The term is also sometimes used in resuscitation research. Stopped blood circulation has historically proven irreversible in most cases. Prior to the invention of
cardiopulmonary resuscitation Cardiopulmonary resuscitation (CPR) is an emergency procedure consisting of chest compressions often combined with artificial ventilation in an effort to manually preserve intact brain function until further measures are taken to restore spont ...
(CPR),
defibrillation Defibrillation is a treatment for life-threatening cardiac arrhythmias, specifically ventricular fibrillation (V-Fib) and non-perfusing ventricular tachycardia (V-Tach). A defibrillator delivers a dose of electric current (often called a ''cou ...
,
epinephrine Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands and ...
injection, and other treatments in the 20th century, the absence of blood circulation (and vital functions related to blood circulation) was historically considered the official definition of
death Death is the irreversible cessation of all biological functions that sustain an organism. For organisms with a brain, death can also be defined as the irreversible cessation of functioning of the whole brain, including brainstem, and brain ...
. With the advent of these strategies, cardiac arrest came to be called ''clinical death'' rather than simply ''death'', to reflect the possibility of post-arrest resuscitation. At the onset of clinical death, consciousness is lost within several seconds, and in dogs, measurable brain activity has been measured to stop within 20 to 40 seconds. Irregular gasping may occur during this early time period, and is sometimes mistaken by rescuers as a sign that CPR is not necessary. During clinical death, all tissues and organs in the body steadily accumulate a type of injury called
ischemic injury Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems wit ...
.


Limits of reversal

Most tissues and organs of the body can survive clinical death for considerable periods. Blood circulation can be stopped in the entire body below the heart for at least 30 minutes, with injury to the spinal cord being a limiting factor. Detached limbs may be successfully reattached after 6 hours of no blood circulation at warm temperatures. Bone, tendon, and skin can survive as long as 8 to 12 hours. The brain, however, appears to accumulate ischemic injury faster than any other organ. Without special treatment after circulation is restarted, full recovery of the brain after more than 3 minutes of clinical death at normal body temperature is rare. Usually brain damage or later brain death results after longer intervals of clinical death even if the heart is restarted and blood circulation is successfully restored. Brain injury is therefore the chief limiting factor for recovery from clinical death. Although loss of function is almost immediate, there is no specific duration of clinical death at which the non-functioning brain clearly dies. The most vulnerable cells in the brain, CA1 neurons of the
hippocampus The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...
, are fatally injured by as little as 10 minutes without oxygen. However, the injured cells do not actually die until hours after resuscitation. This delayed death can be prevented ''
in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology an ...
'' by a simple drug treatment even after 20 minutes without oxygen. In other areas of the brain, viable human
neurons A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...
have been recovered and grown in culture hours after clinical death. Brain failure after clinical death is now known to be due to a complex series of processes called
reperfusion injury Reperfusion injury, sometimes called ischemia-reperfusion injury (IRI) or reoxygenation injury, is the tissue damage caused when blood supply returns to tissue ('' re-'' + ''perfusion'') after a period of ischemia or lack of oxygen (anoxia or hy ...
that occur ''after'' blood circulation has been restored, especially processes that interfere with blood circulation during the recovery period. Control of these processes is the subject of ongoing research. In 1990, the laboratory of resuscitation pioneer
Peter Safar Peter Safar (12 April 19242 August 2003) was an Austrian anesthesiology, anesthesiologist of Czechs, Czech descent. He is credited with pioneering cardiopulmonary resuscitation (CPR). Early life Safar was born in Vienna, Austria, in 1924 into a m ...
discovered that reducing body temperature by three degrees Celsius after restarting blood circulation could double the time window of recovery from clinical death without brain damage from 5 minutes to 10 minutes. This
induced hypothermia Targeted temperature management (TTM) previously known as therapeutic hypothermia or protective hypothermia is an active treatment that tries to achieve and maintain a specific body temperature in a person for a specific duration of time in an e ...
technique is beginning to be used in emergency medicine. The combination of mildly reducing body temperature, reducing blood cell concentration, and increasing blood pressure after resuscitation was found especially effectiveallowing for recovery of dogs after 12 minutes of clinical death at normal body temperature with practically no brain injury. The addition of a drug treatment protocol has been reported to allow recovery of dogs after 16 minutes of clinical death at normal body temperature with no lasting brain injury. Cooling treatment alone has permitted recovery after 17 minutes of clinical death at normal temperature, but with brain injury. Under laboratory conditions at normal body temperature, the longest period of clinical death of a cat (after complete circulatory arrest) survived with eventual return of brain function is one hour.


Hypothermia

Reduced body temperature, or
therapeutic hypothermia Targeted temperature management (TTM) previously known as therapeutic hypothermia or protective hypothermia is an active treatment that tries to achieve and maintain a specific body temperature in a person for a specific duration of time in an e ...
, during clinical death slows the rate of injury accumulation, and extends the time period during which clinical death can be survived. The decrease in the rate of injury can be approximated by the Q10 rule, which states that the rate of biochemical reactions decreases by a factor of two for every 10 °C reduction in temperature. As a result, humans can sometimes survive periods of clinical death exceeding one hour at temperatures below 20 °C. The prognosis is improved if clinical death is caused by hypothermia rather than occurring prior to it; in 1999, 29-year-old Swedish woman Anna Bågenholm spent 80 minutes trapped in ice and survived with a near full recovery from a 13.7 °C core body temperature. It is said in emergency medicine that "nobody is dead until they are warm and dead." In animal studies, up to three hours of clinical death can be survived at temperatures near 0 °C.


Life support

The purpose of
cardiopulmonary resuscitation Cardiopulmonary resuscitation (CPR) is an emergency procedure consisting of chest compressions often combined with artificial ventilation in an effort to manually preserve intact brain function until further measures are taken to restore spont ...
(CPR) during
cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possib ...
is ideally reversal of the clinically dead state by restoration of blood circulation and breathing. However, there is great variation in the effectiveness of CPR for this purpose. Blood pressure is very low during manual CPR, resulting in only a ten-minute average extension of survival. Yet there are cases of patients regaining consciousness during CPR while still in full cardiac arrest. In absence of cerebral function monitoring or frank return to consciousness, the neurological status of patients undergoing CPR is intrinsically uncertain. It is somewhere between the state of clinical death and a normal functioning state. Patients supported by methods that certainly maintain enough blood circulation and oxygenation for sustaining life during stopped heartbeat and breathing, such as
cardiopulmonary bypass Cardiopulmonary bypass (CPB) is a technique in which a machine temporarily takes over the function of the heart and lungs during surgery, maintaining the circulation of blood and oxygen to the body. The CPB pump itself is often referred to as a ...
, are not customarily considered clinically dead. All parts of the body except the heart and lungs continue to function normally. Clinical death occurs only if machines providing sole circulatory support are turned off, leaving the patient in a state of stopped blood circulation.


Controlled

Certain surgeries for
cerebral aneurysm An intracranial aneurysm, also known as a brain aneurysm, is a cerebrovascular disorder in which weakness in the wall of a cerebral artery or vein causes a localized dilation or ballooning of the blood vessel. Aneurysms in the posterior circula ...
s or
aortic arch The aortic arch, arch of the aorta, or transverse aortic arch () is the part of the aorta between the ascending and descending aorta. The arch travels backward, so that it ultimately runs to the left of the trachea. Structure The aorta begins ...
defects require that blood circulation be stopped while repairs are performed. This deliberate temporary induction of clinical death is called circulatory arrest. It is typically performed by lowering body temperature to between 18 °C and 20 °C (64 and 68 °F) and stopping the heart and lungs. This state is called
deep hypothermic circulatory arrest Deep hypothermic circulatory arrest (DHCA) is a surgical technique that induces deep medical hypothermia. It involves cooling the body to temperatures between 20 °C (68  °F) to 25 °C (77 °F), and stopping blood circulation a ...
. At such low temperatures most patients can tolerate the clinically dead state for up to 30 minutes without incurring significant brain injury. Longer durations are possible at lower temperatures, but the usefulness of longer procedures has not been established yet. Controlled clinical death has also been proposed as a treatment for exsanguinating trauma to create time for surgical repair.


Determination

Death was historically believed to be an event that coincided with the onset of clinical death. It is now understood that death is a series of physical events, not a single one, and determination of permanent death is dependent on other factors beyond simple cessation of breathing and heartbeat. Clinical death that occurs unexpectedly is treated as a medical emergency.
CPR Cardiopulmonary resuscitation (CPR) is an emergency procedure consisting of chest compressions often combined with artificial ventilation in an effort to manually preserve intact brain function until further measures are taken to restore sponta ...
is initiated. In a United States hospital, a
Code Blue Hospital emergency codes are coded messages often announced over a public address system of a hospital to alert staff to various classes of on-site emergencies. The use of codes is intended to convey essential information quickly and with minimal ...
is declared and
Advanced Cardiac Life Support Advanced cardiac life support, advanced cardiovascular life support (ACLS) refers to a set of clinical guidelines for the urgent and emergent treatment of life-threatening cardiovascular conditions that will cause or have caused cardiac arrest, ...
procedures used to attempt to restart a normal heartbeat. This effort continues until either the heart is restarted, or a physician determines that continued efforts are useless and recovery is impossible. If this determination is made, the physician pronounces
legal death Legal death is the recognition under the law of a particular jurisdiction that a person is no longer alive. In most cases, a doctor's declaration of death (variously called) or the identification of a corpse is a legal requirement for such recognit ...
and resuscitation efforts stop. If clinical death is expected due to terminal illness or withdrawal of supportive care, often a
Do Not Resuscitate A do-not-resuscitate order (DNR), also known as Do Not Attempt Resuscitation (DNAR), Do Not Attempt Cardiopulmonary Resuscitation (DNACPR), no code or allow natural death, is a medical order, written or oral depending on country, indicating tha ...
(DNR) or "no code" order is in place. This means that no resuscitation efforts are made, and a physician or nurse may pronounce
legal death Legal death is the recognition under the law of a particular jurisdiction that a person is no longer alive. In most cases, a doctor's declaration of death (variously called) or the identification of a corpse is a legal requirement for such recognit ...
at the onset of clinical death. A patient with working heart and lungs who is determined to be
brain dead Brain death is the permanent, irreversible, and complete loss of brain function which may include cessation of involuntary activity necessary to sustain life. It differs from persistent vegetative state, in which the person is alive and some aut ...
can be pronounced
legally dead ''Legally Dead'' is a 1923 American drama film directed by William Parke and written by Harvey Gates. The film stars Milton Sills, Margaret Campbell, Claire Adams, Eddie Sturgis, Faye O'Neill, and Charles A. Stevenson. The film was released ...
without clinical death occurring. However, some courts have been reluctant to impose such a determination over the religious objections of family members, such as in the
Jesse Koochin Jesse Steven Koochin (April 15, 1998 – November 19, 2004)''Social Security Death Index, 1935-2014''. Social Security Administration. was a 6-year-old American boy who became the center of a legal battle between his parents, Steve and Gayle Koochin ...
case. Similar issues were also raised by the case of
Mordechai Dov Brody Mordechai Dov Brody (September 10, 1996 – November 4 or 15, 2008),''Social Security Death Index, 1935-2014''. Social Security Administration. nicknamed Motl or Motyl, was a 12-year-old Hasidic Jewish boy from Brooklyn, New York, United States. Af ...
, but the child died before a court could resolve the matter. Conversely, in the case of Marlise Muñoz, a hospital refused to remove a brain dead woman from life support machines for nearly two months, despite her husband's requests, because she was
pregnant Pregnancy is the time during which one or more offspring develops (gestation, gestates) inside a woman, woman's uterus (womb). A multiple birth, multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occur ...
.


See also


References

{{DEFAULTSORT:Clinical Death Medical aspects of death Intensive care medicine Medical law