COMA

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. 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) to safeguard the airway. The severity of coma impairment is categorized into several levels. Patients may or may not progress through these levels. In the first level, the brain responsiveness lessens, normal reflexes are lost, the patient no longer responds to pain and cannot hear. 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.