A coma is a deep state of unconsciousness - longer-term comatose patients may be reclassified as being in a permanent vegetative state.
The inability to waken differentiates coma from sleep. Levels of unconsciousness and unresponsiveness vary, depending on how much of the brain is functioning.
In this article, we will look at the causes, symptoms, diagnosis and treatment of comas.
Fast facts on coma
Here are some key points about coma. More detail and supporting information is in the main article.
- Patients in a coma do not react to external stimuli
- Comatose patients do not have sleep-wake cycles
- Comas can arise for a number of reasons, including intoxication and nervous system disease
- Depending on the cause, a vegetative state can occur rapidly or gradually
- Sometimes a stroke can result in a coma
- Coma patients do not show normal reflex responses
- A number of tests will be carried out on the patient, often including a spinal tap and MRI scan
- The Glasgow Coma Scale helps assess the severity of the coma
- If there is brain swelling, surgery may be necessary to relieve pressure
What is a coma?
In a comatose state, the patient cannot be awakened and does not respond to pain, light or sound in a normal way - the comatose individual cannot react to the surrounding environment. A person in a coma does not make voluntary actions and does not have sleep-wake cycles.
Individuals in a comatose state do not respond to external stimuli.
A coma is a medical emergency that requires rapid action to preserve life and brain function. Generally, doctors will order a series of blood tests and imaging scans to try to ascertain what the cause of the coma is. Determining the cause usually decides what type of treatment to apply.
Coma may occur for various reasons, such as intoxication, CNS (central nervous system) diseases, a serious injury and hypoxia (oxygen deprivation). Coma can be induced deliberately with pharmaceutical agents - perhaps in order to protect the patient from intense pain during a healing process, or to preserve higher brain function following another form of brain trauma.
Comas generally do not last for more than a few weeks. A patient whose state does not change after an extended period is often reclassified as being in a persistent vegetative state. Unfortunately, those in a persistent vegetative state for over twelve months rarely wake up.
The English medical word "coma" comes from the Ancient Greek word Koma, meaning "deep sleep."
Symptoms of a coma
A symptom is something the patient feels and reports, while a sign is something other people, such as the doctor detect. For example, pain may be a symptom while a rash may be a sign. As a comatose patient does not communicate, there are only signs:
- Closed eyes
- Limbs do not respond, except for reflex movements
- There is no response to painful stimuli, except for reflex movements.
The severity and duration of signs and symptoms that lead up to the loss of consciousness may vary and depend on the underlying cause. For example, worsening hypoglycemia (low blood sugar) or hypercapnia (higher blood CO2 levels) will cause mild agitation at first, eventually there will be obtundation (less than full mental capacity), stupor and finally loss of consciousness.
On the other hand, coma caused by a severe injury to the brain or a subarachnoid hemorrhage will occur instantaneously. Doctors are especially interested in what occurred leading up to the coma, because that helps them determine what the underlying cause was and what treatment to apply.
When doctors initially assess a coma, they will typically try to gauge the level of consciousness by spontaneously exhibited actions. The AVPU scale is an example; the abbreviation stands for
- Vocal stimuli
- Painful stimuli
More elaborate scales also exist, such as the Glasgow coma scale (see further down this page). Patients with deep unconsciousness are assessed for risk of asphyxiation - if it is high some type of device may be used to secure the airways, such as an oropharyngeal airway, nasopharyngeal airway or endotracheal tube.
Causes of a coma
There are multiple ways in which a coma might occur, including diabetes and infection
A coma can have several possible causes, including:
- Diabetes: if the blood sugar levels of the diabetes patient rise too much they will have hyperglycemia, the opposite is hypoglycemia (blood sugar levels are too low). Sustained periods of hyperglycemia or hypoglycemia can result in coma
- Hypoxia (lack of oxygen): a person who nearly drowned may not awaken because of a shortage of blood (which carries oxygen) to the brain. The same may occur if somebody is resuscitated after a heart attack
- Infections: those which cause inflammation of the brain, spinal cord or tissues surrounding the brain can result in coma if symptoms are severe enough. Examples include encephalitis or meningitis
- Stroke: a condition where a blood clot or ruptured artery or blood vessel interrupts blood flow to an area of the brain. A lack of oxygen and glucose (sugar) flowing to the brain leads to the death of brain cells and brain damage, often resulting in impairment in speech, movement, and memory - and sometimes coma
- Toxins and drug overdoses: exposure to carbon monoxide can result in brain damage and coma, as can some drug overdoses
- Traumatic brain injuries: these include injuries from vehicle accidents and violent attacks. They are the most common cause of comas.
On the next page, we look at diagnosis and treatment of coma.