[1] The person may experience respiratory and circulatory problems due to the body's inability to maintain normal bodily functions.

People in a coma often require extensive medical care to maintain their health and prevent complications such as pneumonia or blood clots.

[9][10] 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).

[16] Lack of oxygen in the brain also causes ATP exhaustion and cellular breakdown from cytoskeleton damage and nitric oxide production.

[18] Comatose cases can also result from traumatic brain injury, excessive blood loss, malnutrition, hypothermia, hyperthermia, hyperammonemia,[19] abnormal glucose levels, and many other biological disorders.

Injury to either or both of the cerebral cortex or the reticular activating system (RAS) is sufficient to cause a person to enter coma.

[23] White matter is responsible for perception, relay of the sensory input via the thalamic pathway, and many other neurological functions, including complex thinking.

[15] Any impairment in ARAS functioning, a neuronal dysfunction, along the arousal pathway stated directly above, prevents the body from being aware of its surroundings.

[2] 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.

[27] By contrast, a diffuse cause is limited to aberrations of cellular function which fall under a metabolic or toxic subgroup.

Hypoglycemia or hypercapnia initially cause mild agitation and confusion, but progress to obtundation, stupor, and finally, complete unconsciousness.

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.

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, etc.)

[38] 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).

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:[9] A coma can be classified as (1) supratentorial (above Tentorium cerebelli), (2) infratentorial (below Tentorium cerebelli), (3) metabolic or (4) diffused.

In the first level, the brain responsiveness lessens, normal reflexes are lost, the patient no longer responds to pain and cannot hear.

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.

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 (from the trachea to the lungs).

This trapping of matter in their lower respiratory tract can ultimately lead to infection, resulting in aspiration pneumonia.

[49] Predicted chances of recovery will differ depending on which techniques were used to measure the patient's severity of neurological damage.

The most common cause of death for a person in a vegetative state is secondary infection such as pneumonia, which can occur in patients who lie still for extended periods.

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, the inability to articulate any speech.

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.

After 19 years in a minimally conscious state, Terry Wallis spontaneously began speaking and regained awareness of his surroundings.

Perspectives on personhood, identity and consciousness come into play when discussing the metaphysical and bioethical views on comas.

[55] 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.

That said, because experiencing positiveness is a basic emotional process with phylogenetic roots, it is likely to occur at a completely unaware level and, therefore, introduces the idea of an unconscious well-being.

"[56] 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.