Forty percent of comas begin with drug poisoning
A coma is prolonged deep unconsciousness: no waking, weak responses to pain, light or sound, and no normal sleep–wake cycle. Clinicians sometimes treat failure to obey even a single simple instruction as the working bedside definition. Drug poisoning alone explains about forty percent of comatose states.
The word comes from the Greek koma, deep sleep, but a coma is not sleep. Staying conscious needs two things at once: wakefulness, which is a matter of degree, and awareness, which is about content. A comatose person has lost both. Bedside signs include no reaction to pain or speech, pupils that ignore light, breathing that may be irregular or absent after cardiac arrest, and a Glasgow Coma Scale score between 3 and 8.
Damage to either of two regions is enough. One is the cerebral cortex, the grey outer layer of the brain; the other is the reticular activating system, an older network in the brainstem whose ascending tract keeps the cortex switched on. Causes fall into structural ones, such as pressure or a blocked vessel, and diffuse ones that disturb neurons chemically. The two can feed each other: low blood sugar left untreated can end up causing physical damage.
Poisoning by drugs accounts for about 40% of cases, typically by dampening that brainstem arousal system. Oxygen starvation, usually after the heart stops, causes roughly a quarter, because neurons are exceptionally hungry for oxygen. Strokes, bleeds and tumours account for about a fifth more. The rest include head injury, with about one traumatic brain injury patient in eight becoming comatose, along with blood loss, extreme body temperatures, kidney or liver failure, seizures and brain infections such as meningitis.
Recognising a coma is easy; finding its cause is not. After securing airway, breathing and circulation, clinicians rule out mimics. People with locked-in syndrome can still move their eyes deliberately, and those with psychogenic unresponsiveness resist having their eyelids opened. Then come blood tests for drugs and salts, CT or MRI scans to look for bleeding or herniation, and EEG monitoring for hidden seizures. Because throat muscles slacken, choking is a real danger, so airway protection comes first.
Source: Coma
