A coma is a deep state of prolonged
unconsciousness
Unconsciousness is a state in which a living individual exhibits a complete, or near-complete, inability to maintain an consciousness, awareness of self and environment or to respond to any human or environmental Stimulus (physiology), stimulus. ...
in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions.
Coma patients exhibit a complete absence of wakefulness and are unable to consciously feel, speak or move.
Comas can be derived by natural causes, or can be
medically induced.
Clinically, a coma can be defined as the inability consistently to follow a one-step command. It can also be defined as a score of ≤ 8 on the
Glasgow Coma Scale
The Glasgow Coma Scale (GCS) is a clinical scale used to reliably measure a person's level of consciousness after a brain injury.
The GCS assesses a person based on their ability to perform eye movements, speak, and move their body. These thre ...
(GCS) lasting ≥ 6 hours. For a patient to maintain consciousness, the components of ''wakefulness'' and ''awareness'' must be maintained.
Wakefulness
Wakefulness is a daily recurring Human brain, brain state and state of consciousness in which an individual is conscious and engages in coherent cognition, cognitive and behavioral responses to the external world.
Being awake is the opposite of ...
describes the quantitative degree of
consciousness
Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
, whereas
awareness
Awareness is the state of being conscious of something. More specifically, it is the ability to directly know and perceive, to feel, or to be cognizant of events. Another definition describes it as a state wherein a subject is aware of some inform ...
relates to the qualitative aspects of the functions mediated by the cortex, including cognitive abilities such as attention, sensory perception, explicit memory, language, the execution of tasks, temporal and spatial orientation and reality judgment.
From a neurological perspective, consciousness is maintained by the activation of the
cerebral cortex
The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of ...
—the
gray matter
Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distinguis ...
that forms the outer layer of the brain—and by the
reticular activating system
The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formatio ...
(RAS), a structure located within the
brainstem
The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...
.
Etymology
The term 'coma', from the Greek ''koma'', meaning deep sleep, had already been used in the
Hippocratic corpus
The Hippocratic Corpus (Latin: ''Corpus Hippocraticum''), or Hippocratic Collection, is a collection of around 60 early Ancient Greek medical works strongly associated with the physician Hippocrates and his teachings. The Hippocratic Corpus cove ...
(''Epidemica'') and later by
Galen
Aelius Galenus or Claudius Galenus ( el, Κλαύδιος Γαληνός; September 129 – c. AD 216), often Anglicized as Galen () or Galen of Pergamon, was a Greek physician, surgeon and philosopher in the Roman Empire. Considered to be one of ...
(second century AD). Subsequently, it was hardly used in the known literature up to the middle of the 17th century. The term is found again in
Thomas Willis
Thomas Willis FRS (27 January 1621 – 11 November 1675) was an English doctor who played an important part in the history of anatomy, neurology and psychiatry, and was a founding member of the Royal Society.
Life
Willis was born on his pare ...
' (1621–1675) influential ''De anima brutorum'' (1672), where
lethargy
Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overwo ...
(pathological sleep), 'coma' (heavy sleeping), ''carus'' (deprivation of the senses) and
apoplexy
Apoplexy () is rupture of an internal organ and the accompanying symptoms. The term formerly referred to what is now called a stroke. Nowadays, health care professionals do not use the term, but instead specify the anatomic location of the bleedi ...
(into which ''carus'' could turn and which he localized in the
white matter
White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distribution ...
) are mentioned. The term ''carus'' is also derived from Greek, where it can be found in the roots of several words meaning soporific or sleepy. It can still be found in the root of the term 'carotid'.
Thomas Sydenham
Thomas Sydenham (10 September 1624 – 29 December 1689) was an English physician. He was the author of ''Observationes Medicae'' which became a standard textbook of medicine for two centuries so that he became known as 'The English Hippocrate ...
(1624–89) mentioned the term 'coma' in several cases of fever (Sydenham, 1685).
Signs and symptoms
General symptoms of a person in a comatose state are:
* Inability to voluntarily open the eyes
* A non-existent sleep-wake cycle
* Lack of response to physical (painful) or verbal stimuli
* Depressed brainstem reflexes, such as pupils not responding to light
* Irregular breathing
* Scores between 3 and 8 on the
Glasgow Coma Scale
The Glasgow Coma Scale (GCS) is a clinical scale used to reliably measure a person's level of consciousness after a brain injury.
The GCS assesses a person based on their ability to perform eye movements, speak, and move their body. These thre ...
Causes
Many types of problems can cause a coma. Forty percent of comatose states result from
drug poisoning
A drug overdose (overdose or OD) is the ingestion or application of a drug or other substance in quantities much greater than are recommended. .
Certain drug use under certain conditions can damage or weaken the
synaptic functioning in the
ascending reticular activating system
The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formatio ...
(ARAS) and keep the system from properly functioning to arouse the brain.
Secondary effects of drugs, which include abnormal heart rate and blood pressure, as well as abnormal breathing and sweating, may also indirectly harm the functioning of the ARAS and lead to a coma. Given that drug poisoning is the cause for a large portion of patients in a coma, hospitals first test all comatose patients by observing pupil size and eye movement, through the
vestibular-ocular reflex. (See ''Diagnosis'' below.)
The second most common cause of coma, which makes up about 25% of cases, is lack of oxygen, generally resulting from
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
Central Nervous System (CNS) requires a great deal of oxygen for its
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 ...
. Oxygen deprivation in the
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
, also known as
hypoxia
Hypoxia means a lower than normal level of oxygen, and may refer to:
Reduced or insufficient oxygen
* Hypoxia (environmental), abnormally low oxygen content of the specific environment
* Hypoxia (medical), abnormally low level of oxygen in the tis ...
, causes sodium and calcium from outside of the
neuron
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 ...
s to decrease and intracellular calcium to increase, which harms neuron communication. Lack of oxygen in the brain also causes
ATP exhaustion and cellular breakdown from cytoskeleton damage and
nitric oxide
Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...
production.
Twenty percent of comatose states result from the side effects of a stroke.
During a stroke, blood flow to part of the brain is restricted or blocked. An
ischemic stroke
A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
,
brain hemorrhage
Intracerebral hemorrhage (ICH), also known as cerebral bleed, intraparenchymal bleed, and hemorrhagic stroke, or haemorrhagic stroke, is a sudden bleeding into the tissues of the brain, into its ventricles, or into both. It is one kind of bleed ...
, or tumor may cause restriction of blood flow. Lack of blood to cells in the brain prevents oxygen from getting to the neurons, and consequently causes cells to become disrupted and die. As brain cells die, brain tissue continues to deteriorate, which may affect the functioning of the ARAS.
The remaining 15% of comatose cases result from trauma, excessive
blood loss
Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vag ...
,
malnutrition
Malnutrition occurs when an organism gets too few or too many nutrients, resulting in health problems. Specifically, it is "a deficiency, excess, or imbalance of energy, protein and other nutrients" which adversely affects the body's tissues a ...
,
hypothermia
Hypothermia is defined as a body core temperature below in humans. Symptoms depend on the temperature. In mild hypothermia, there is shivering and mental confusion. In moderate hypothermia, shivering stops and confusion increases. In severe h ...
,
hyperthermia
Hyperthermia, also known simply as overheating, is a condition in which an individual's body temperature is elevated beyond normal due to failed thermoregulation. The person's body produces or absorbs more heat than it dissipates. When extreme ...
,
hyperammonemia
Hyperammonemia is a metabolic disturbance characterised by an excess of ammonia in the blood. It is a dangerous condition that may lead to brain injury and death. It may be primary or secondary.
Ammonia is a substance that contains nitrogen. It i ...
, abnormal glucose levels, and many other biological disorders. Furthermore, studies show that 1 out of 8 patients with traumatic brain injury experience a comatose state.
Pathophysiology
Injury to either or both of the
cerebral cortex
The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of ...
or the
reticular activating system
The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formatio ...
(RAS) is sufficient to cause a person to enter coma.
The
cerebral cortex
The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of ...
is the outer layer of
neural tissue
Nervous tissue, also called neural tissue, is the main tissue component of the nervous system. The nervous system regulates and controls body functions and activity. It consists of two parts: the central nervous system (CNS) comprising the brain ...
of the
cerebrum
The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In ...
of the
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
. The cerebral cortex is composed of
gray matter
Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distinguis ...
which consists of the
nuclei of
neuron
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 ...
s, whereas the inner portion of the
cerebrum
The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In ...
is composed of
white matter
White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distribution ...
and is composed of the
axon
An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action po ...
s of
neuron
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 ...
. White matter is responsible for
perception
Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system ...
, relay of the sensory input via the thalamic pathway, and many other neurological functions, including complex thinking.
The RAS, on the other hand, is a more primitive structure in the
brainstem
The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...
which includes the
reticular formation
The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. It is not anatomically well defined, because it includes neurons located in different parts of the brain. The neurons of the reticular formation ...
(RF).
The RAS has two tracts, the ascending and descending tract. The ascending tract, or ascending reticular activating system (ARAS), is made up of a system of acetylcholine-producing neurons, and works to arouse and wake up the brain. Arousal of the brain begins from the RF, through the
thalamus
The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, ...
, and then finally to the cerebral cortex.
Any impairment in ARAS functioning, a neuronal dysfunction, along the arousal pathway stated directly above, prevents the body from being aware of its surroundings.
Without the arousal and consciousness centers, the body cannot awaken, remaining in a comatose state.
The severity and mode of onset of coma depends on the underlying cause. There are two main subdivisions of a coma: structural and diffuse neuronal. A structural cause, for example, is brought upon by a mechanical force that brings about cellular damage, such as physical pressure or a blockage in neural transmission. While a diffuse cause is limited to aberrations of cellular function, that fall under a metabolic or toxic subgroup. Toxin-induced comas are caused by extrinsic substances, whereas metabolic-induced comas are caused by intrinsic processes, such as body thermoregulation or ionic imbalances(e.g. sodium).
For instance, severe
hypoglycemia
Hypoglycemia, also called low blood sugar, is a fall in blood sugar to levels below normal, typically below 70 mg/dL (3.9 mmol/L). Whipple's triad is used to properly identify hypoglycemic episodes. It is defined as blood glucose belo ...
(low blood sugar) or
hypercapnia
Hypercapnia (from the Greek ''hyper'' = "above" or "too much" and ''kapnos'' = "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous pro ...
(increased
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
levels in the blood) are examples of a metabolic diffuse neuronal dysfunction. Hypoglycemia or hypercapnia initially cause mild agitation and confusion, but progress to
obtundation
Obtundation refers to less than full alertness (altered level of consciousness), typically as a result of a medical condition or trauma.
There is a huge range of potential causes including head injury, interruption of blood circulation, impaired ...
, stupor, and finally, complete
unconsciousness
Unconsciousness is a state in which a living individual exhibits a complete, or near-complete, inability to maintain an consciousness, awareness of self and environment or to respond to any human or environmental Stimulus (physiology), stimulus. ...
. In contrast, coma resulting from a severe
traumatic brain injury
A traumatic brain injury (TBI), also known as an intracranial injury, is an injury to the brain caused by an external force. TBI can be classified based on severity (ranging from mild traumatic brain injury TBI/concussionto severe traumatic b ...
or
subarachnoid hemorrhage
Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater surrounding the brain. Symptoms may include a severe headache of rapid onset, vomiting, decreased level of consci ...
can be instantaneous. The mode of onset may therefore be indicative of the underlying cause.
Structural and diffuse causes of coma are not isolated from one another, as one can lead to the other in some situations. For instance, coma induced by a diffuse metabolic process, such as hypoglycemia, can result in a structural coma if it is not resolved. Another example is if cerebral edema, a diffuse dysfunction, leads to ischemia of the brainstem, a structural issue, due to the blockage of the circulation in the brain.
Diagnosis
Although diagnosis of coma is simple, investigating the underlying cause of onset can be rather challenging. As such, after gaining stabilization of the patient's airways, breathing and circulation (the basic
ABCs) various diagnostic tests, such as physical examinations and imaging tools (
CT scan,
MRI
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...
, etc.) are employed to access the underlying cause of the coma.
When an unconscious person enters a hospital, the hospital utilizes a series of diagnostic steps to identify the cause of
unconsciousness
Unconsciousness is a state in which a living individual exhibits a complete, or near-complete, inability to maintain an consciousness, awareness of self and environment or to respond to any human or environmental Stimulus (physiology), stimulus. ...
. According to Young,
the following steps should be taken when dealing with a patient possibly in a coma:
# Perform a general examination and medical history check
# Make sure the patient is in an actual comatose state and is not in a
locked-in state or experiencing psychogenic unresponsiveness. Patients with
locked-in syndrome
Locked-in syndrome (LIS), also known as pseudocoma, is a condition in which a patient is aware but cannot move or communicate verbally due to complete paralysis of nearly all voluntary muscles in the body except for vertical eye movements and bli ...
present with voluntary movement of their eyes, whereas patients with
psychogenic coma
A psychogenic effect is one that originates from the brain instead of other physical organs (i.e. the cause is psychological rather than physiological) and may refer to:
*Psychogenic pain
*Psychogenic disease
*Psychogenic amnesia
*Psychogenic co ...
s demonstrate active resistance to passive opening of the eyelids, with the eyelids closing abruptly and completely when the lifted upper eyelid is released (rather than slowly, asymmetrically and incompletely as seen in comas due to organic causes).
# Find the site of the brain that may be causing coma (e.g.,
brainstem
The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...
, back of brain...) and assess the severity of the coma with the
Glasgow Coma Scale
The Glasgow Coma Scale (GCS) is a clinical scale used to reliably measure a person's level of consciousness after a brain injury.
The GCS assesses a person based on their ability to perform eye movements, speak, and move their body. These thre ...
# Take blood work to see if drugs were involved or if it was a result of
hypoventilation
Hypoventilation (also known as respiratory depression) occurs when ventilation is inadequate (''hypo'' meaning "below") to perform needed respiratory gas exchange. By definition it causes an increased concentration of carbon dioxide (hypercapnia ...
/
hyperventilation
Hyperventilation is irregular breathing that occurs when the rate or tidal volume of breathing eliminates more carbon dioxide than the body can produce. This leads to hypocapnia, a reduced concentration of carbon dioxide dissolved in the blood. ...
# Check for levels of serum glucose, calcium, sodium, potassium, magnesium, phosphate, urea, and creatinine
# Perform brain scans to observe any abnormal brain functioning using either
CT or
MRI
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...
scans
# Continue to monitor brain waves and identify
seizures
An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or neural oscillation, synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much o ...
of patient using
EEGs
Initial evaluation
In the initial assessment of coma, it is common to gauge the
level of consciousness
An altered level of consciousness is any measure of arousal other than normal. Level of consciousness (LOC) is a measurement of a person's arousability and responsiveness to stimuli from the environment.
A mildly depressed level of consciousne ...
on the
AVPU The AVPU scale (an acronym from "alert, verbal, pain, unresponsive") is a system by which a health care professional can measure and record a patient's level of consciousness. It is mostly used in emergency medicine protocols, and within first aid.
...
(alert, vocal stimuli, painful stimuli, unresponsive) scale by spontaneously exhibiting actions and, assessing the patient's response to vocal and painful stimuli. More elaborate scales, such as the
Glasgow Coma Scale
The Glasgow Coma Scale (GCS) is a clinical scale used to reliably measure a person's level of consciousness after a brain injury.
The GCS assesses a person based on their ability to perform eye movements, speak, and move their body. These thre ...
, quantify an individual's reactions such as eye opening, movement and verbal response in order to indicate their extent of brain injury. The patient's score can vary from a score of 3 (indicating severe brain injury and death) to 15 (indicating mild or no brain injury).
In those with deep unconsciousness, there is a risk of
asphyxiation
Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can i ...
as the control over the muscles in the face and throat is diminished. As a result, those presenting to a hospital with coma are typically assessed for this risk ("
airway management
Airway management includes a set of maneuvers and medical procedures performed to prevent and relieve airway obstruction. This ensures an open pathway for gas exchange between a patient's lungs and the atmosphere. This is accomplished by either cl ...
"). If the risk of asphyxiation is deemed high, doctors may use various devices (such as an
oropharyngeal airway
An oropharyngeal airway (also known as an oral airway, OPA or Guedel pattern airway) is a medical device called an ''airway adjunct'' used in airway management to maintain or open a patient's airway. It does this by preventing the tongue from cover ...
,
nasopharyngeal airway
In medicine, a nasopharyngeal airway, also known as an NPA, nasal trumpet (because of its flared end), or nose hose, is a type of ''airway adjunct'', a tube that is designed to be inserted through the nasal passage down into the posterior pharynx ...
or
endotracheal tube
A tracheal tube is a catheter that is inserted into the trachea for the primary purpose of establishing and maintaining a patent airway and to ensure the adequate exchange of oxygen and carbon dioxide.
Many different types of tracheal tubes are a ...
) to safeguard the airway.
Imaging and testing
Imaging basically encompasses
computed tomography (CAT or CT) scan of the brain, or
MRI
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...
for example, and is performed to identify specific causes of the coma, such as
hemorrhage
Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vag ...
in the brain or
herniation
A hernia is the abnormal exit of tissue or an organ, such as the bowel, through the wall of the cavity in which it normally resides. Various types of hernias can occur, most commonly involving the abdomen, and specifically the groin. Groin herni ...
of the brain structures. Special tests such as an
EEG
Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...
can also show a lot about the activity level of the cortex such as semantic processing,
presence of
seizures
An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or neural oscillation, synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much o ...
, and are important available tools not only for the assessment of the cortical activity but also for predicting the likelihood of the patient's awakening.
The autonomous responses such as the
skin conductance response
Electrodermal activity (EDA) is the property of the human body that causes continuous variation in the electrical characteristics of the Human skin, skin. Historically, EDA has also been known as skin conductance, galvanic skin response (GSR), el ...
may also provide further insight on the patient's emotional processing.
In the treatment of traumatic brain injury (TBI), there are 4 examination methods that have proved useful: skull x-ray, angiography, computed tomography (CT), and magnetic resonance imaging (MRI). The skull x-ray can detect linear fractures, impression fractures (expression fractures) and burst fractures. Angiography is used on rare occasions for TBIs i.e. when there is suspicion of an aneurysm, carotid sinus fistula, traumatic vascular occlusion, and vascular dissection. A CT can detect changes in density between the brain tissue and hemorrhages like subdural and intracerebral hemorrhages. MRIs are not the first choice in emergencies because of the long scanning times and because fractures cannot be detected as well as CT. MRIs are used for the imaging of soft tissues and lesions in the posterior fossa which cannot be found with the use of CT.
Body movements
Assessment of the brainstem and cortical function through special reflex tests such as the
oculocephalic reflex test (doll's eyes test),
oculovestibular reflex test (cold caloric test),
corneal reflex
The corneal reflex, also known as the blink reflex or eyelid reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea (such as by touching or by a foreign body), though it could result from any peripheral stimulus. S ...
, and the
gag reflex The pharyngeal reflex or gag reflex is a reflex muscular contraction of the back of the throat, evoked by touching the roof of the mouth, the back of the tongue, the area around the tonsils, the uvula, and the back of the throat. It, along with othe ...
. Reflexes are a good indicator of what
cranial nerves
Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...
are still intact and functioning and is an important part of the physical exam. Due to the unconscious status of the patient, only a limited number of the nerves can be assessed. These include the cranial nerves number 2 (CN II), number 3 (CN III), number 5 (CN V), number 7 (CN VII), and cranial nerves 9 and 10 (CN IX, CN X).
![Decorticate](https://upload.wikimedia.org/wikipedia/commons/2/2a/Decorticate.PNG)
Assessment of posture and physique is the next step. It involves general observation about the patient's positioning. There are often two stereotypical postures seen in comatose patients.
Decorticate posturing
Abnormal posturing is an involuntary flexion or extension of the arms and legs, indicating severe brain injury. It occurs when one set of muscles becomes incapacitated while the opposing set is not, and an external stimulus such as pain cau ...
is a stereotypical posturing in which the patient has arms
flexed at the elbow, and arms adducted toward the body, with both legs
extended.
Decerebrate posturing
Abnormal posturing is an involuntary flexion or extension of the arms and legs, indicating severe brain injury. It occurs when one set of muscles becomes incapacitated while the opposing set is not, and an external stimulus such as pain cau ...
is a stereotypical posturing in which the legs are similarly extended (stretched), but the arms are also stretched (extended at the elbow). The posturing is critical since it indicates where the damage is in the central nervous system. A decorticate posturing indicates a lesion (a point of damage) at or above the
red nucleus
The red nucleus or nucleus ruber is a structure in the rostral midbrain involved in motor coordination. The red nucleus is pale pink, which is believed to be due to the presence of iron in at least two different forms: hemoglobin and ferritin. ...
, whereas a decerebrate posturing indicates a lesion at or below the red nucleus. In other words, a decorticate lesion is closer to the
cortex
Cortex or cortical may refer to:
Biology
* Cortex (anatomy), the outermost layer of an organ
** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain''
*** Motor cortex, the regions of the cerebral cortex i ...
, as opposed to a decerebrate posturing which indicates that the lesion is closer to the
brainstem
The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is cont ...
.
Pupil size
Pupil assessment is often a critical portion of a comatose examination, as it can give information as to the cause of the coma; the following table is a technical, medical guideline for common pupil findings and their possible interpretations:
Severity
A coma can be classified as (1)
supratentorial In anatomy, the supratentorial region of the brain is the area located above the tentorium cerebelli. The area of the brain below the tentorium cerebelli is the infratentorial region. The supratentorial region contains the cerebrum, while the infra ...
(above
Tentorium cerebelli
The cerebellar tentorium or tentorium cerebelli (Latin for "tent of the cerebellum") is an extension of the dura mater that separates the cerebellum from the inferior portion of the occipital lobes.
Structure
The cerebellar tentorium is an arche ...
), (2)
infratentorial
In anatomy, the infratentorial region of the brain is the area located below the tentorium cerebelli. The area of the brain above the tentorium cerebelli is the supratentorial region. The infratentorial region contains the cerebellum
The cerebe ...
(below Tentorium cerebelli), (3) metabolic or (4) diffused.
This classification is merely dependent on the position of the original damage that caused the coma, and does not correlate with severity or the prognosis. The severity of coma impairment however is categorized into several levels. Patients may or may not progress through these levels. In the first level, the brain responsiveness lessens, normal reflexes are lost, the patient no longer responds to pain and cannot hear.
The
Rancho Los Amigos Scale
The Rancho Los Amigos Scale (RLAS), a.k.a. the Rancho Los Amigos Levels of Cognitive Functioning Scale (LOCF) or Rancho Scale, is a medical scale used to assess individuals after a closed head injury, including traumatic brain injury, based on co ...
is a complex scale that has eight separate levels, and is often used in the first few weeks or months of coma while the patient is under closer observation, and when shifts between levels are more frequent.
Treatment
Treatment for people in a coma will depend on the severity and cause of the comatose state. Upon admittance to an emergency department, coma patients will usually be placed in an
Intensive Care Unit
220px, Intensive care unit
An intensive care unit (ICU), also known as an intensive therapy unit or intensive treatment unit (ITU) or critical care unit (CCU), is a special department of a hospital or health care facility that provides intensiv ...
(ICU) immediately,
where maintenance of the patient's respiration and circulation become a first priority. Stability of their respiration and circulation is sustained through the use of
intubation
Intubation (sometimes entubation) is a medical procedure involving the insertion of a tube into the body. Patients are generally anesthetized beforehand. Examples include tracheal intubation, and the balloon tamponade with a Sengstaken-Blakemo ...
,
ventilation
Ventilation may refer to:
* Ventilation (physiology), the movement of air between the environment and the lungs via inhalation and exhalation
** Mechanical ventilation, in medicine, using artificial methods to assist breathing
*** Ventilator, a ma ...
, administration of
intravenous
Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrie ...
fluids or blood and other supportive care as needed.
Continued care
Once a patient is stable and no longer in immediate danger, there may be a shift of priority from stabilizing the patient to maintaining the state of their physical wellbeing. Moving patients every 2–3 hours by turning them side to side is crucial to avoiding
bed sores
Pressure ulcers, also known as pressure sores, bed sores or pressure injuries, are localised damage to the skin and/or underlying tissue that usually occur over a bony prominence as a result of usually long-term pressure, or pressure in combi ...
as a result of being confined to a bed. Moving patients through the use of
physical therapy
Physical therapy (PT), also known as physiotherapy, is one of the allied health professions. It is provided by physical therapists who promote, maintain, or restore health through physical examination, diagnosis, management, prognosis, patient ...
also aids in preventing
atelectasis
Atelectasis is the collapse or closure of a lung resulting in reduced or absent gas exchange. It is usually unilateral, affecting part or all of one lung. It is a condition where the alveoli are deflated down to little or no volume, as distinct ...
,
contracture
In pathology, a contracture is a permanent shortening of a muscle or joint. It is usually in response to prolonged hypertonic spasticity in a concentrated muscle area, such as is seen in the tightest muscles of people with conditions like spasti ...
s or other orthopedic deformities which would interfere with a coma patient's recovery.
Pneumonia is also common in coma patients due to their inability to swallow which can then lead to
aspiration. A coma patient's lack of a gag reflex and use of a feeding tube can result in food, drink or other solid organic matter being lodged within their
lower respiratory tract
The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa.
Air is breathed in through the nose to th ...
(from the trachea to the lungs). This trapping of matter in their lower respiratory tract can ultimately lead to infection, resulting in
aspiration pneumonia
Aspiration pneumonia is a type of lung infection that is due to a relatively large amount of material from the stomach or mouth entering the lungs. Signs and symptoms often include fever and cough of relatively rapid onset. Complications may inclu ...
.
Coma patients may also deal with restlessness or seizures. As such, soft cloth restraints may be used to prevent them from pulling on tubes or dressings and side rails on the bed should be kept up to prevent patients from falling.
Caregivers
Coma has a wide variety of emotional reactions from the family members of the affected patients, as well as the primary care givers taking care of the patients. Research has shown that the severity of injury causing coma was found to have no significant impact compared to how much time has passed since the injury occurred. Common reactions, such as desperation, anger, frustration, and denial are possible. The focus of the patient care should be on creating an amicable relationship with the family members or dependents of a comatose patient as well as creating a rapport with the medical staff. Although there is heavy importance of a primary care taker, secondary care takers can play a supporting role to temporarily relieve the primary care taker's burden of tasks.
Prognosis
Comas can last from several days to, in particularly extreme cases, years. Some patients eventually gradually come out of the coma, some progress to a
vegetative state
A persistent vegetative state (PVS) or post-coma unresponsiveness (PCU) is a disorder of consciousness in which patients with severe brain damage are in a state of partial arousal rather than true awareness. After four weeks in a vegetative stat ...
, and others die. Some patients who have entered a vegetative state go on to regain a degree of awareness; and in some cases may remain in vegetative state for years or even decades (
the longest recorded period is 42 years).
Predicted chances of recovery will differ depending on which techniques were used to measure the patient's severity of neurological damage. Predictions of recovery are based on
statistical
Statistics (from German: ''Statistik'', "description of a state, a country") is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a scientific, industria ...
rates, expressed as the level of chance the person has of recovering. Time is the best general predictor of a chance of recovery. For example, after four months of coma caused by
brain damage
Neurotrauma, brain damage or brain injury (BI) is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors. In general, brain damage refers to significant, undiscriminating t ...
, the chance of partial recovery is less than 15%, and the chance of full recovery is very low.
The outcome for coma and vegetative state depends on the cause, location, severity and extent of neurological damage. A deeper coma alone does not necessarily mean a slimmer chance of recovery; similarly, a milder coma does not indicate a higher chance of recovery. The most common cause of death for a person in a vegetative state is secondary
infection
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...
such as
pneumonia
Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...
, which can occur in patients who lie still for extended periods.
Recovery
People may emerge from a coma with a combination of physical, intellectual, and psychological difficulties that need special attention. It is common for coma patients to awaken in a profound state of confusion and experience
dysarthria
Dysarthria is a speech sound disorder resulting from neurological injury of the motor component of the motor–speech system and is characterized by poor articulation of phonemes. In other words, it is a condition in which problems effectively ...
, the inability to articulate any speech. Recovery is usually gradual. In the first days, the patient may only awaken for a few minutes, with increased duration of wakefulness as their recovery progresses, and they may eventually recover full awareness. That said, some patients may never progress beyond very basic responses.
There are reports of people coming out of a coma after long periods of time. After 19 years in a
minimally conscious state
A minimally conscious state (MCS) is a disorder of consciousness distinct from persistent vegetative state and locked-in syndrome. Unlike persistent vegetative state, patients with MCS have partial preservation of conscious awareness. MCS is a rel ...
,
Terry Wallis
Terry Wayne Wallis (April 7, 1964 – March 29, 2022) was an American man from the Ozark Mountains of Arkansas who, on June 11, 2003, regained awareness after spending 19 years in a minimally conscious state.
Early life
Wallis was born on April ...
spontaneously began speaking and regained awareness of his surroundings.
A man with brain-damage and trapped in a coma-like state for six years, was brought back to consciousness in 2003 by doctors who planted electrodes deep inside his brain. The method, called
deep brain stimulation
Deep brain stimulation (DBS) is a neurosurgical procedure involving the placement of a medical device called a neurostimulator, which sends electrical impulses, through implanted electrodes, to specific targets in the brain (the brain nucleu ...
(DBS), successfully roused communication, complex movement and eating ability in the 38-year-old American man with a traumatic brain injury. His injuries left him in a minimally conscious state, a condition akin to a coma but characterized by occasional, but brief, evidence of environmental and self-awareness that coma patients lack.
Society and culture
Research by Dr. Eelco Wijdicks on the depiction of comas in movies was published in Neurology in May 2006. Dr. Wijdicks studied 30 films (made between 1970 and 2004) that portrayed actors in prolonged comas, and he concluded that only two films accurately depicted the state of a coma patient and the agony of waiting for a patient to awaken: ''
Reversal of Fortune
''Reversal of Fortune'' is a 1990 American drama film adapted from the 1985 book ''Reversal of Fortune: Inside the von Bülow Case'', written by law professor Alan Dershowitz. It recounts the true story of the unexplained coma of socialite Sunny ...
'' (1990) and ''
The Dreamlife of Angels
''The Dreamlife of Angels'' (french: La Vie rêvée des anges) is a 1998 French drama film directed by Erick Zonca. The film was selected as the French entry for the Best Foreign Language Film at the 71st Academy Awards, but was not accepted as ...
'' (1998). The remaining 28 were criticized for portraying miraculous awakenings with no lasting side effects, unrealistic depictions of treatments and equipment required, and comatose patients remaining muscular and tanned.
Bioethics
A person in a coma is said to be in an
unconscious
Unconscious may refer to:
Physiology
* Unconsciousness, the lack of consciousness or responsiveness to people and other environmental stimuli
Psychology
* Unconscious mind, the mind operating well outside the attention of the conscious mind a ...
state. Perspectives on
personhood
Personhood or personality is the status of being a person. Defining personhood is a controversial topic in philosophy and law and is closely tied with legal and political concepts of citizenship, equality, and liberty. According to law, only a leg ...
,
identity
Identity may refer to:
* Identity document
* Identity (philosophy)
* Identity (social science)
* Identity (mathematics)
Arts and entertainment Film and television
* ''Identity'' (1987 film), an Iranian film
* ''Identity'' (2003 film), ...
and
consciousness
Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
come into play when discussing the
metaphysical
Metaphysics is the branch of philosophy that studies the fundamental nature of reality, the first principles of being, identity and change, space and time, causality, necessity, and possibility. It includes questions about the nature of conscio ...
and
bioethical
Bioethics is both a field of study and professional practice, interested in ethical issues related to health (primarily focused on the human, but also increasingly includes animal ethics), including those emerging from advances in biology, med ...
views on comas.
It has been argued that unawareness should be just as ethically relevant and important as a state of awareness and that there should be metaphysical support of unawareness as a state.
In the ethical discussions about disorders of consciousness (DOCs), two abilities are usually considered as central: ''experiencing well-being'' and ''having interest''. Well-being can broadly be understood as the positive effect related to what makes life good (according to specific standards) for the individual in question.
The only condition for well-being broadly considered is the ability to experience its 'positiveness'. That said, because experiencing positiveness is a basic emotional process with
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
roots, it is likely to occur at a completely unaware level and therefore, introduces the idea of an unconscious well-being.
[ ]
Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
As such, the ability of having interests, is crucial for describing two abilities which those with comas are deficient in. Having an interest in a certain domain can be understood as having a stake in something that can affect what makes our life good in that domain. An interest is what directly and immediately improves life from a certain point of view or within a particular domain, or greatly increases the likelihood of life improvement enabling the subject to realize some good.
That said, sensitivity to reward signals is a fundamental element in the learning process, both consciously and unconsciously.
Moreover, the unconscious brain is able to interact with its surroundings in a meaningful way and to produce meaningful information processing of stimuli coming from the external environment, including other people.
According to Hawkins, "1. A life is good if the subject is able to value, or more basically if the subject is able to care. Importantly, Hawkins stresses that caring has no need for cognitive commitment, i.e. for high-level cognitive activities: it requires being able to distinguish something, track it for a while, recognize it over time, and have certain emotional dispositions ''vis-à-vis'' something. 2. A life is good if the subject has the capacity for relationship with others, i.e. for meaningfully interacting with other people."
This suggests that unawareness may (at least partly) fulfill both conditions identified by Hawkins for life to be good for a subject, thus making the unconscious ethically relevant.
See also
*
Brain death
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 ...
, lack of activity in both cortex, and lack of brainstem function
*
Coma scale
A coma scale is a system to assess the severity of coma. There are several such systems:
Glasgow Coma Scale
The Glasgow Coma Scale is neurology, neurological Scale (ratio), scale which aims to give a reliable, objective way of recording the cons ...
, a system to assess the severity of coma
*
Locked-in syndrome
Locked-in syndrome (LIS), also known as pseudocoma, is a condition in which a patient is aware but cannot move or communicate verbally due to complete paralysis of nearly all voluntary muscles in the body except for vertical eye movements and bli ...
, paralysis of most muscles, except ocular muscles of the eyes, while patient is conscious
*
Persistent vegetative state
A persistent vegetative state (PVS) or post-coma unresponsiveness (PCU) is a disorder of consciousness in which patients with severe brain damage are in a state of partial arousal rather than true awareness. After four weeks in a vegetative stat ...
(vegetative coma), deep coma without detectable awareness. Damage to the cortex, with an intact brainstem.
*
Process Oriented Coma Work
Process-oriented psychology, also called process work, is a depth psychology theory and set of techniques developed by Arnold Mindell and associated with transpersonal psychology,Collins, M. (2001). Who Is Occupied ? Consciousness, Self Awareness ...
, for an approach to working with residual consciousness in comatose patients.
*
Suspended animation
Suspended animation is the temporary (short- or long-term) slowing or stopping of biological function so that physiological capabilities are preserved. It may be either hypometabolic or ametabolic in nature. It may be induced by either endogen ...
, the inducement of a temporary cessation or decay of main body functions.
References
External links
{{Authority control
Intensive care medicine
Emergency medicine
Symptoms and signs of mental disorders