coma
Meaning of coma: A state of unrousable unresponsiveness that resembles sleep from the outside and works nothing like it within.
Definition of coma
Coma is a state of deep unresponsiveness in which a person cannot be woken by speech, touch or pain, keeps the eyes closed, and makes no purposeful movement. It reflects failure of the brain systems that generate wakefulness, whether from widespread injury to both halves of the brain or from damage to the brainstem. It is a state rather than a diagnosis, and it always has an underlying cause.
How does it differ from sleep?
In every way that matters, despite the resemblance that named it. Sleep is an active, organized process the brain produces and cycles through, and a sleeping person wakes when shaken or spoken to loudly. Someone in a coma does not, whatever is tried. The cycling itself is absent: the alternation between light sleep, deep sleep and REM sleep that runs through every night disappears, and recordings of brain activity show none of the patterns belonging to a normal sleep stage. The eyes stay shut because the machinery that opens them has stopped working, not because the person is resting.
What causes it?
| Category | Examples |
|---|---|
| Structural injury | Severe head injury, large stroke, bleeding, a tumor with swelling |
| Loss of fuel or oxygen | Cardiac arrest, suffocation, a very low blood sugar |
| Poisoning | Alcohol, sedatives, opioids, carbon monoxide |
| Metabolic upset | Liver or kidney failure, extreme sodium shifts, uncontrolled diabetes |
| Infection or inflammation | Meningitis, encephalitis, overwhelming infection |
| Seizure activity | Continuing seizures, and the deep state following them |
What states are confused with it?
Several, and the differences carry real weight. A vegetative state, now also termed unresponsive wakefulness, follows when the sleep and waking cycle returns but awareness does not, so the eyes open and rove without following anything. A minimally conscious state shows fragments of awareness that come and go. Locked-in syndrome looks like unresponsiveness from the bedside, yet the person is fully awake and aware and paralyzed except for eye movements, through which communication is possible. Brain death is the irreversible loss of all brain function including the drive to breathe, and it is a determination of death rather than a depth of coma. Coma itself rarely persists more than a few weeks, resolving toward recovery, passing into one of these other states, or ending in death.
Also known as
Used in a sentence
The patient remained in a coma following the cardiac arrest.
Good to know
Coma is not sleep, since the cycles of sleep are absent and no stimulus produces waking, and it is distinguished from the vegetative and minimally conscious states, from locked-in syndrome and from brain death.
Word origin
Where “coma” comes from
Coma comes from the Greek koma, meaning deep sleep, a comparison the state deserves only from the outside.