Coma

Coma is the deepest state of unconsciousness. Comatose people 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.

Consciousness is controlled by the the activation of the cerebral cortex—the gray matter that forms the outer layer of the brain—and by the reticular activating system (RAS), a structure located within the brainstem of the brain.

Comas are caused by injuries to the brain. It can result from lack of oxygen to the brain or conditions of the brain.

## Etymology

The term 'coma', from the Greek κῶμα *koma*, meaning deep sleep, had already been used in the Hippocratic corpus (*Epidemica*) and later by Galen (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' (1621–1675) influential *De anima brutorum* (1672), where lethargy (pathological sleep), 'coma' (heavy sleeping), *carus* (deprivation of the senses) and apoplexy (into which *carus* could turn and which he localized in the white matter) 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 (1624–89) mentioned the term 'coma' in several cases of fever (Sydenham, 1685).

## Symptoms

Symptoms of coma include:

* 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
* Problems with breathing

## Causes

Coma has many causes, but the most common medical conditions that cause coma include:

* Traumatic brain injury: Head injuries can cause the brain to swell and/or bleed. When the brain swells as a result of trauma, the fluid pushes up against the skull. The swelling may eventually cause the brain to push down on the brain stem, which can damage the RAS (Reticular Activating System) -- a part of the brain that's responsible for arousal and awareness.
* Brain hemorrhage: Bleeding in the layers of the brain may cause coma due to swelling and compression on the injured side of the brain. This compression causes the brain to shift, causing damage to the brainstem and the RAS (mentioned above). High blood pressure, ruptured cerebral aneurysms, and tumors are non-traumatic causes of bleeding in the brain.
* Ischemic stroke: When there is no blood flow to a major part of the brain or loss of blood accompanied with swelling, coma can occur.
* Cardiac arrest: Cardiac arrest causes a sudden cutoff of blood flow and oxygen to the brain, called hypoxia or anoxia, which causes coma. After cardiopulmonary resuscitation (CPR), survivors of cardiac arrest are often in comas.
* Infections involving the brain: Infections of the central nervous system, such as meningitis or encephalitis, can also cause coma due to swelling of the brain.
* Brain tumor: Tumors in the brain or the brain stem can cause coma due to swelling of the brain.
* Seizures/Epilepsy: A single seizure rarely produces coma. But continuous seizures -- called status epilepticus -- can. Repeated seizures can prevent the brain from recovering in between seizures. This will cause prolonged unconsciousness and coma.
* Respiratory arrest: Respiratory arrest causes lack of oxygen to the brain, called hypoxia or anoxia, which causes coma.

Other medical conditions that causes coma include:

* Heart attack
* Heart failure
* Cardiogenic shock
* Severe arrhythmia
* Severe infection of the heart or heart valves
* Kidney failure
* Liver failure
* Heat stroke
* Diabetes
* Excessive or severe blood loss

Coma also has metabolic causes. Metabolic causes of coma include:

* Hyperglycemia
* Hypoglycemia
* Hyperthermia
* Hyperpyrexia
* Hypothermia
* Hypocholesterolemia
* Hypokalemia
* Hypotension in severe cases

Drowning, electrocution, choking, and poisoning can also cause coma due to lack of oxygen to the brain.

Comas can also be medically-induced. Medically-induced comas are different from natural comas because medically-induced comas are induced to prevent the brain from damage.

## 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 (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, ventilation, administration of intravenous fluids or blood and other supportive care as needed.