In medicine, a coma (from the Greek κῶμα koma, meaning deep sleep) 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.
Coma may result from a variety of conditions, including intoxication, metabolic abnormalities, central nervous system diseases, acute neurologic injuries such as stroke, and hypoxia. A coma may also result from head trauma caused by mechanisms such as falls or car accidents. It may also be deliberately induced by pharmaceutical agents in order to preserve higher brain function following another form of brain trauma, or to save the patient from extreme pain during healing of injuries or diseases. The underlying cause of coma is bilateral damage to the Reticular formation of the midbrain, which is important in regulating sleep.
If the cause of coma is not clear, various investigations (blood tests, medical imaging) may be performed to establish the cause and identify reversible causes. Coma usually necessitates admission to hospital and often the intensive care unit.
The severity and mode of onset of coma depends on the underlying cause. For instance, deepening hypoglycemia (low blood sugars) or hypercapnia (increased carbon dioxide levels in the blood) initially causes mild agitation and confusion, then progressing to obtundation, stupor and finally complete unconsciousness. In contrast, coma resulting from a severe traumatic brain injury or subarachnoid hemorrhage can be instantaneous. The mode of onset may therefore be indicative of the underlying cause.
In the initial assessment of coma, it is common to gauge the level of consciousness by spontaneously exhibited actions, response to vocal stimuli ("can you hear me"?), and painful stimuli; this is known as the AVPU (alert, vocal stimuli, painful stimuli, unconscious) scale. More elaborate scales, such as the Glasgow coma scale (see below), quantify individual reactions such as eye opening, movement and verbal response on a scale.
In those with deep unconsciousness, there is a risk of asphyxiation as the control over the muscles in the face and throat is diminished. As a result, those presenting to hospital with coma are typically assessed for this risk ("airway management"). If the risk of asphyxiation is deemed to be high, doctors may use various devices (such as an oropharyngeal airway, nasopharyngeal airway or endotracheal tube) so safeguard the airway.
Once a person in a coma is stable, investigations are performed to assess the underlying cause. These may be simple, such as, a computed tomography scan of the brain is performed to identify specific causes of coma, such as hemorrhage.
Two scales of measurement often used in Traumatic Brain Injury (TBI) diagnosis to determine the level of coma are the Glasgow Coma Scale (GCS) and the Ranchos Los Amigos Scale (RLAS). The GCS is a simple 3 to 15-point scale (3 being the worst and 15 being that of a normal person) used by medical professionals to assess severity of neurologic trauma, and establish a prognosis. The RLAS is a more 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.
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, because some people in deep coma recover well while others in a so-called milder coma sometimes fail to improve.
People may emerge from a coma with a combination of physical, intellectual and psychological difficulties that need special attention. Recovery usually occurs gradually — patients acquire more and more ability to respond. Some patients never progress beyond very basic responses, but many recover full awareness. Regaining consciousness is not instant: in the first days, patients are only awake for a few minutes, and duration of time awake gradually increases.
Predicted chances of recovery are variable owing to different techniques used to measure the extent of neurological damage. All the predictions are based on statistical rates with some level of chance for recovery present: a person with a low chance of recovery may still awaken. Time is the best general predictor of a chance of recovery: after 4 months of coma caused by brain damage, the chance of partial recovery is less than 15%, and the chance of full recovery is very low.
Occasionally people come out of coma after long periods of time. After 19 years in a minimally conscious state, Terry Wallis spontaneously began speaking and regained awareness of his surroundings. Similarly, Polish railroad worker Jan Grzebski woke up from a 19-year coma in 2007.
A brain-damaged man, 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 (DBS) successfully roused communication, complex movement and eating ability in the 38-year-old American man who suffered a traumatic brain injury. His injuries left him in a minimally conscious state (MCS), a condition akin to a coma but characterized by occasional, but brief, evidence of environmental and self-awareness that coma patients lack.