Coma

Did You Know?

• Treatment for coma patients includes moving them every 2–3 hours to avoid bed sores and using physical therapy to prevent atelectasis, contractures, or other orthopedic deformities.
• After four 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.
• Some patients who have entered a vegetative state may remain in that state for years or even decades.

Causes

Many types of problems can cause a coma. Forty percent of comatose states result from drug poisoning, which can damage or weaken synaptic functioning in the ascending reticular activating system (ARAS) and keep it from properly arousing the brain. Secondary effects of drugs, such as abnormal heart rate, blood pressure, breathing, and sweating, may also indirectly harm ARAS functioning. The second most common cause, accounting for about 25% of cases, is lack of oxygen, generally from cardiac arrest. Cerebral hypoxia harms neuron communication by decreasing sodium and calcium outside neurons and increasing intracellular calcium, and also causes ATP exhaustion and cellular breakdown. Twenty percent of comatose states result from an ischemic stroke, brain hemorrhage, or brain tumor, which restrict blood flow to the brain, preventing oxygen from reaching neurons and causing cell death. Comatose cases can also result from traumatic brain injury, excessive blood loss, malnutrition, hypothermia, hyperthermia, hyperammonemia, abnormal glucose levels, and many other biological disorders. Heart-related causes include cardiac arrest, ventricular fibrillation, ventricular tachycardia, atrial fibrillation, myocardial infarction, heart failure, severe arrhythmia, cardiogenic shock, myocarditis, and pericarditis. Respiratory arrest is the only lung condition that causes coma.

Pathophysiology

A coma can occur when there is damage to the cerebral cortex, the reticular activating system (RAS), or both. The cerebral cortex is the brain's outer layer, made of gray matter packed with neuron cell bodies, while the inner cerebrum consists of white matter made of axons. The RAS is an older part of the brainstem that includes the reticular formation. Its ascending branch, the ascending reticular activating system (ARAS), uses acetylcholine-producing neurons to wake the brain. This arousal pathway runs from the reticular formation through the thalamus to the cerebral cortex. If the ARAS is impaired anywhere along this route, the brain cannot become aware of its surroundings, leading to a coma.

Comas fall into two main categories: structural and diffuse neuronal. Structural comas result from mechanical force that causes physical damage, like pressure or blocked neural signals. Diffuse neuronal comas stem from problems in cell function, split into metabolic or toxic causes. Toxic comas come from outside substances, while metabolic comas arise from internal issues such as body temperature problems or ionic imbalances like sodium levels. For example, severe hypoglycemia or hypercapnia starts with mild agitation and confusion, then moves through obtundation and stupor to complete unconsciousness. In contrast, a coma from a severe traumatic brain injury or subarachnoid hemorrhage can happen instantly. The speed of onset often hints at the underlying cause.

Diagnosis

Although diagnosis of coma is simple, investigating the underlying cause can be challenging. After stabilizing the patient's airways, breathing, and circulation, various diagnostic tests are used. Steps include performing a general examination and medical history check; ensuring the patient is not in a locked-in state or experiencing psychogenic unresponsiveness (locked-in patients show voluntary eye movement, while psychogenic patients actively resist eyelid opening); finding the brain site causing coma and assessing severity with the Glasgow Coma Scale; taking blood work to check for drugs or hypoventilation/hyperventilation; checking levels of serum glucose, calcium, sodium, potassium, magnesium, phosphate, urea, and creatinine; performing brain scans using CT or MRI; and monitoring brain waves with EEG to identify seizures. Initial assessment often uses the AVPU scale (alert, vocal stimuli, painful stimuli, unresponsive) by observing spontaneous actions and responses to vocal and painful stimuli. The Glasgow Coma Scale quantifies eye opening, movement, and verbal response, with scores ranging from 3 (severe brain injury and death) to 15 (mild or no brain injury).

Society and culture

A 2006 study in the journal Neurology examined how comas are shown in movies. The researcher looked at 30 films from 1970 to 2004 where characters were in long-term comas. Only two films were found to be realistic: Reversal of Fortune (1990) and The Dreamlife of Angels (1998). The other 28 movies were criticized for showing patients waking up suddenly with no lasting problems, using fake-looking medical equipment, and keeping comatose patients fit and tanned. When thinking about comas from a philosophical or ethical angle, ideas about personhood, identity, and consciousness matter. Some argue that being unaware should be taken as seriously as being aware, and that this state deserves its own philosophical support. In ethics around disorders of consciousness, two key abilities are usually discussed: the ability to experience well-being and the ability to have interests. Well-being means a positive feeling tied to what makes life good for a person. Since basic positive feelings can happen without awareness, the idea of unconscious well-being exists. Having an interest means having a stake in something that can affect how good life is in a certain area. People in comas lack these abilities. Still, the unconscious brain can process information from the outside world and respond to it in meaningful ways.