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Level of consciousness (LOC) is a measurement of a person's arousability
Arousal

Arousal is a physiology and psychology state of being awake. It involves the activation of the reticular activating system in the brain stem, the autonomic nervous system and the endocrine system, leading to increased heart rate and blood pressure and a condition of sensory alertness, mobility and readiness to respond....
 and responsiveness to stimuli
Stimulus (physiology)

In physiology, a stimulus is a detectable change in the internal or external environment. When a stimulus is applied to a sensory receptor, it elicits or influences a Reflex action via Transduction ....
 from the environment. A mildly depressed level of consciousness
Consciousness

Consciousness is a difficult term to define, because the word is used and understood in a wide variety of ways, so that it frequently happens that what one person sees as a definition of consciousness is seen by others as about something else altogether....
 may be classed as lethargy; someone in this state can be aroused with little difficulty. People who are obtunded have a more depressed level of consciousness and cannot be fully aroused. Those who are not able to be aroused from a sleep-like state are said to be stuporous
Stupor

Stupor is the lack of critical cognitive function and level of consciousness wherein a sufferer is almost entirely unresponsive and only responds to base stimuli such as pain....
.






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Level of consciousness (LOC) is a measurement of a person's arousability
Arousal

Arousal is a physiology and psychology state of being awake. It involves the activation of the reticular activating system in the brain stem, the autonomic nervous system and the endocrine system, leading to increased heart rate and blood pressure and a condition of sensory alertness, mobility and readiness to respond....
 and responsiveness to stimuli
Stimulus (physiology)

In physiology, a stimulus is a detectable change in the internal or external environment. When a stimulus is applied to a sensory receptor, it elicits or influences a Reflex action via Transduction ....
 from the environment. A mildly depressed level of consciousness
Consciousness

Consciousness is a difficult term to define, because the word is used and understood in a wide variety of ways, so that it frequently happens that what one person sees as a definition of consciousness is seen by others as about something else altogether....
 may be classed as lethargy; someone in this state can be aroused with little difficulty. People who are obtunded have a more depressed level of consciousness and cannot be fully aroused. Those who are not able to be aroused from a sleep-like state are said to be stuporous
Stupor

Stupor is the lack of critical cognitive function and level of consciousness wherein a sufferer is almost entirely unresponsive and only responds to base stimuli such as pain....
. Coma
Coma

In medicine, a coma is a profound state of unconsciousness. A comatose person cannot be awakened, fails to respond normally to pain or light, does not have sleep-wake cycles, and does not take voluntary actions....
 is the inability to make any purposeful response. Scales such as the Glasgow coma scale
Glasgow Coma Scale

The Glasgow Coma Scale or GCS, sometimes also known as the Glasgow Coma Score is a neurology Scale which aims to give a reliable, objective way of recording the conscious state of a person, for initial as well as continuing assessment....
 have been designed to measure level of consciousness.

An altered level of consciousness can result from a variety of factors, including alterations in the chemical environment of the brain (e.g. exposure to poison
Poison

In the context of biology, poisons are Chemical substance that can cause disturbances to organisms, usually by chemical reaction or other activity on the molecular scale, when a sufficient quantity is absorbed by an organism....
s), insufficient oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
 or blood flow
Blood flow

Blood flow is the flow of blood in the cardiovascular system.It can be calculated by dividing the vascular resistance into the pressure gradient....
 in the brain, and excessive pressure within the skull
Intracranial pressure

Intracranial pressure, , is the pressure in the cranium and thus in the brain tissue and cerebrospinal fluid ; this pressure is exerted on the brain's intracranial blood circulation vessels....
. Prolonged unconsciousness is understood to be a sign of a medical emergency
Medical emergency

A medical emergency is an injury or illness that is Acute and poses an immediate risk to a person's life or long term health. These emergencies may require assistance from another person, who should ideally be suitably qualified to do so, although some of these emergencies can be dealt with by the victim themselves....
. A deficit in the level of consciousness suggests that both of the cerebral hemisphere
Cerebral hemisphere

A cerebral hemisphere is defined as one of the two regions of the brain that are delineated by the body's Anatomical_position#Median_and_sagittal_plane, ....
s or the reticular activating system
Reticular activating system

The reticular activating system is the name given to the part of the brain believed to be the center of arousal and motivation in mammals ....
 have been injured. A decreased level of consciousness correlates to increased morbidity (disability
Disability

Disability is a lack of ability relative to a personal or group standard or norm. In reality there is often simply a spectrum of ability. Disability may involve physical impairment such as sense impairment, cognitive impairment or intellectual impairment, mental disorder , or various types of chronic disease....
) and mortality
Mortality rate

Mortality rate is a measure of the number of deaths in some population, scaled to the size of that population, per unit time. Mortality rate is typically expressed in units of deaths per 1000 individuals per year; thus, a mortality rate of 9.5 in a population of 100,000 would mean 950 deaths per year in that entire population....
 (death). Thus it is a valuable measure of a patient's medical and neurological status. In fact, some sources consider level of consciousness to be one of the vital signs.

Levels

 Levels of consciousness
Level Description
Conscious Normal
ConfusedDisoriented; impaired thinking and responses
DeliriousDisoriented; restlessness, hallucinations, sometimes delusions
ObtundedDecreased alertness; slowed psychomotor responses
Stuporous Sleep-like state (not unconscious); little/no spontaneous activity
Comatose Cannot be aroused; no response to stimuli


Scales and terms to classify the levels of consciousness differ, but in general, reduction in response to stimuli indicates decreasing level of consciousness (see table at right). Assessment of LOC involves checking orientation
Orientation

Orientation may refer to:* Orientation , a function of the mind* Orientation , determining ones location in ones surroundings* Orientation , a 1996 short film produced by the Church of Scientology...
: people who are able promptly and spontaneously to state their name, location, and the date or time are said to be oriented to self, place, and time, or "oriented X3". A normal sleep
Sleep

Sleep is the natural state of bodily rest observed in humans and other animals. It is common to all mammals and birds, and is also seen in many reptiles, amphibians and fish....
 stage from which a person is easily awakened is also considered a normal level of consciousness. "Clouding of consciousness" is a term for a mild alteration of consciousness with alterations in attention and wakefulness. People who do not respond quickly with information about their name, location, and the time are considered "obtuse" or "confused
ConFusion

ConFusion is an annual science fiction convention organized by the Stilyagi Air Corps and its parent organization, the Ann Arbor Science Fiction Association....
". A confused person may be bewildered, disoriented, and have difficulty following instructions. Some scales have "delirious" below this level, in which a person may be restless or agitated and exhibit a marked deficit in attention
Attention

Attention is the cognitive process of selectively concentrating on one aspect of the environment while ignoring other things. Examples include listening carefully to what someone is saying while ignoring other conversations in a room or listening to a cell phone conversation while driving a car....
. A somnolent
Somnolence

Somnolence is a state of near-sleep, a strong desire for sleep, or sleeping for unusually long periods . It has two distinct meanings, referring both to the usual state preceding falling asleep, and the chronic condition referring to being in that state independent of a circadian rhythm....
 person shows excessive drowsiness and responds to stimuli only with incoherent mumbles or disorganized movements. In obtundation, a person has a decreased interest in the surroundings, slowed responses, and sleepiness. People with an even lower level of consciousness, stupor, only respond by grimacing
Grimace

Grimace may refer to:*A character in McDonaldland*A type of facial expression*A Grimace active in the mid-to-late 14th century...
 or drawing away from painful stimuli. Comatose people do not even make this response to stimuli, have no corneal
Corneal reflex

The corneal reflex, also known as the blink reflex, is an involuntary blinking of the eyelids elicited by stimulation of the cornea, or bright light, though could result from any peripheral stimulus....
 or gag reflex
Gag reflex

The pharyngeal reflex or gag reflex is a reflex contraction of the back of the throat, evoked by touching the soft palate. It prevents something from entering the throat except as part of normal swallowing and helps prevent choking....
, and they may have no pupillary response
Pupillary response

Pupillary response or dilation of the pupil is a physiological response that varies the size of the pupil of the eye via the iris dilator muscle....
 to light.

Causes of alteration


A lowered level of consciousness can indicate a deficit in brain function. Level of consciousness can be lowered when the brain receives insufficient oxygen (as occurs in hypoxia
Hypoxia (medical)

Hypoxia is a Pathology condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise....
); insufficient blood (as occurs in shock); or has an alteration in the brain's chemistry. Metabolic disorders such as diabetes mellitus
Diabetes mellitus

Diabetes mellitus , often referred to simply as diabetes , is a syndrome of disordered metabolism, usually due to a combination of genetic disorder and environmental causes, resulting in abnormally high blood sugar levels ....
 and uremia
Uremia

Uremia is a term used to loosely describe the illness accompanying renal failure , in particular the nitrogenous waste products associated with the failure of this organ....
 can alter consciousness. Hypo-
Hyponatremia

Hyponatremia is an electrolyte disturbance in which the sodium concentration in the blood plasma is too low .Severe or rapidly progressing hyponatremia can result in swelling of the brain , and the symptoms of hyponatremia are mainly neurology....
 or hypernatremia
Hypernatremia

Hypernatremia or hypernatraemia is an electrolyte disturbance that is defined by an elevated sodium level in the blood. Hypernatremia is generally not caused by an excess of sodium, but rather by a relative deficit of water in the body....
 (decreased and elevated levels of sodium
Sodium

Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....
, respectively) as well as dehydration
Dehydration

Dehydration is the removal of water from an object. In Physiology terms, it entails a relative deficiency of water molecules in relation to other dissolved solutes....
 can also produce an altered LOC. A pH
PH

pH is a measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations....
 outside of the range the brain can tolerate will also alter LOC. Exposure to drug
Drug

A drug, broadly speaking, is any chemical substance that, when absorbed into the body of a living organism, alters normal bodily function....
s, alcohol
Alcohol

In chemistry, an alcohol is any organic compound in which a hydroxyl Functional group is bound to a carbon atom of an alkyl or substituted alkyl group....
 or toxin
Toxin

A toxin is a poisonous substance produced by living cells or organisms. For a toxic substance not produced by living organisms, "toxicant" is the more appropriate term, and "toxics" is an acceptable plural....
s may also lower LOC, as may a core temperature
Core temperature

#REDIRECT Normal human body temperature...
 that is too high or too low (hyperthermia
Hyperthermia

Hyperthermia, in its advanced state referred to as heat stroke or sunstroke, is an acute condition which occurs when the body produces or absorbs more heat than it can dissipate....
 or hypothermia
Hypothermia

Hypothermia is a condition in which an organism's temperature drops below that required for normal metabolism and bodily functions. In warm-blooded animals, core body temperature is maintained near a constant level through biologic homeostasis....
). Increases in intracranial pressure
Intracranial pressure

Intracranial pressure, , is the pressure in the cranium and thus in the brain tissue and cerebrospinal fluid ; this pressure is exerted on the brain's intracranial blood circulation vessels....
 (the pressure within the skull) can also cause altered LOC. It can result from traumatic brain injury
Traumatic brain injury

Traumatic brain injury occurs when an outside force physical trauma the brain. TBI can be classified based on severity, mechanism , or other features ....
 such as concussion. Stroke
Stroke

A stroke is the rapidly developing loss of brain function due to a disturbance in the blood supply to the brain. According to the National Stroke Association, a "stroke" occurs when a blood clot blocks and artery or a blood vessel breaks, interrupting blood flow to an area of the brain....
 and intracranial hemorrhage
Intracranial hemorrhage

An intracranial hemorrhage is a hemorrhage, or bleeding, within the skull....
 are other causes. Infection
Infection

An infection is the detrimental colonization of a host organism by a foreign species. In an infection, the infecting organism seeks to utilize the host resources to multiply ....
s of the central nervous system
Central nervous system

The central nervous system is the part of the nervous system that functions to coordinate the activity of all parts of the bodies of multicellular organisms....
 may also be associated with decreased LOC; for example, an altered LOC is the most common symptom of encephalitis
Encephalitis

Not to be confused with syphilis, although that can cause encephalitis as well.Encephalitis is an Acute inflammation of the brain.Encephalitis with meningitis is known as meningoencephalitis....
. Neoplasms within the intracranial cavity can also affect consciousness, as can epilepsy
Epilepsy

Epilepsy is a common chronic neurological disorder characterized by recurrent unprovoked seizure s. These seizures are transient signs and/or symptoms of abnormal, excessive or synchronous neuronal activity in the brain....
 and post-seizure state
Postictal state

The postictal state is the altered state of consciousness that a person enters after experiencing an epilepsy seizure, such as those occurring with frontal lobe epilepsy....
s. A decreased LOC can also result from a combination of factors.

Neuroscience

Although the neural science behind alertness, wakefulness, and arousal are not fully known, the reticular formation
Reticular formation

The reticular formation is a part of the brain that is involved in actions such as awaking/sleep cycle, and filtering incoming stimuli to discriminate irrelevant background stimuli....
 is known to play a role in these. The ascending reticular activating system is a postulated group of neural connections that receives sensory input and projects to the cerebral cortex
Cerebral cortex

The cerebral cortex is a structure within the brain that plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness....
 through the midbrain and thalamus
Thalamus

The thalamus is a pair and symmetric part of the brain. It constitutes the main part of the diencephalon....
 from the retucular formation. Since this system is thought to modulate wakefulness and sleep, interference with it, such as injury, illness, or metabolic disturbances, could alter the level of consciousness.

Normally, stupor and coma are produced by interference with the brain stem
Brain stem

The brain stem is the lower part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves....
, such as can be caused by a lesion
Lesion

A lesion is any abnormal tissue found on or in an organism, usually damaged by disease or trauma. Lesion is derived from the Latin word laesio which means injury....
 or indirect effects, such as brain herniation
Brain herniation

Brain herniation, also known as cistern obliteration, is a deadly side effect of very high intracranial pressure that occurs when the brain shifts across structures within the skull....
. Mass lesions in the brain stem normally cause coma due to their effects on the reticular formation. Mass lesion
Lesion

A lesion is any abnormal tissue found on or in an organism, usually damaged by disease or trauma. Lesion is derived from the Latin word laesio which means injury....
s that occur above
Supratentorial

In anatomy the supratentorial region of the brain is the part located above the tentorium cerebelli; the part of the brain below it is the infratentorial region....
 the tentorium cerebelli
Tentorium cerebelli

The tentorium cerebelli or cerebellar tentorium is an extension of the dura mater that separates the cerebellum from the inferior portion of the occipital lobes....
 (pictured) normally do not significantly alter the level of consciousness unless they are very large or affect both cerebral hemisphere
Cerebral hemisphere

A cerebral hemisphere is defined as one of the two regions of the brain that are delineated by the body's Anatomical_position#Median_and_sagittal_plane, ....
s.

Assessment

Assessing LOC involves determining an individual's response to external stimuli. Speed and accuracy of responses to questions and reactions to stimuli such as touch and pain are noted. Reflex
ReFLEX

ReFLEX is a wireless protocol developed by Motorola which is used for two-way paging.The Motorola PageWriter released in 1996 was one of the first devices to use the ReFLEX network protocol....
es, such as the cough and gag reflexes, are also means of judging LOC. Once the level of consciousness is determined, clinicians seek clues for the cause of any alteration.

Measurement

One tool for measuring LOC objectively, Glasgow Coma Scale
Glasgow Coma Scale

The Glasgow Coma Scale or GCS, sometimes also known as the Glasgow Coma Score is a neurology Scale which aims to give a reliable, objective way of recording the conscious state of a person, for initial as well as continuing assessment....
 (GCS), has come into almost universal use for assessing people with brain injury. Verbal, motor, and eye-opening responses to stimuli are measured, scored, and added into a final score on a scale of 3–15, with a lower score being a more decreased level of consciousness.

The Grady Coma Scale classes patients on a scale of I to V along a scale of confusion, stupor, deep stupor, abnormal posturing
Abnormal 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 causes the working set of muscles to contract....
, and coma.

The AVPU
AVPU

The AVPU scale is a system by which a first aider, ambulance crew or health care professional can measure and record a patient's level of consciousness....
 scale is another means of measuring LOC: patients are assessed to determine whether they are alert, responsive to verbal stimuli, responsive to painful stimuli, or unresponsive. To determine responsiveness to voice, a caregiver speaks to, or, failing that, yells at the paitent. Responsiveness to pain is determined with a mild painful stimulus such as a pinch; moaning or withdrawal from the stimulus is considered a response to pain. The ACDU scale, like AVPU, is easier to use than the GCS and produces similarly accurate results. Using ACDU, a patient is assessed for alertness, confusion, drowsiness, and unresponsiveness.