Coma

Jai Ganesh · 2023-12-10 21:44:26

Coma

Gist

Coma is a state of prolonged loss of consciousness. It can have a variety of causes, including traumatic head injury, stroke, brain tumor, or drug or alcohol intoxication. A coma may even be caused by an underlying illness, such as diabetes or an infection. Coma is a medical emergency.

Summary

Coma is a medical emergency. Quick action is needed to preserve life and brain function. Health care providers typically order a series of blood tests and a brain scan to try to learn what's causing the coma so that proper treatment can begin.

A coma doesn't usually last longer than several weeks. People who are unconscious for a longer time might transition to a lasting vegetative state, known as a persistent vegetative state, or brain death.

Symptoms

The symptoms of a coma commonly include:

* Closed eyes.
* Depressed brainstem reflexes, such as pupils not responding to light.
* No responses of limbs except for reflex movements.
* No response to painful stimuli except for reflex movements.
* Irregular breathing.

When to see a doctor

A coma is a medical emergency. Seek immediate medical care for the person in a coma.

Causes

Many types of problems can cause a coma. Some examples are:

* Traumatic brain injuries. These are often caused by traffic collisions or acts of violence.
* Stroke. Reduced or stopped blood supply to the brain, known as a stroke, can result from blocked arteries or a burst blood vessel.
* Tumors. Tumors in the brain or brainstem can cause a coma.
* Diabetes. Blood sugar levels that become too high or too low can cause a coma.
* Lack of oxygen. People who have been rescued from drowning or revived after a heart attack might not awaken due to lack of oxygen to the brain.
* Infections. Infections such as encephalitis and meningitis cause swelling of the brain, spinal cord or the tissues that surround the brain. Severe cases of these infections can result in brain damage or a coma.
* Seizures. Ongoing seizures can lead to a coma.
* Toxins. Exposure to toxins, such as carbon monoxide or lead, can cause brain damage and a coma.
* Drugs and alcohol. Overdosing on drugs or alcohol can result in a coma.

Complications

Although many people gradually recover from a coma, others enter a persistent vegetative state or die. Some people who recover from a coma end up with major or minor disabilities.

During a coma, bedsores, urinary tract infections, blood clots in the legs and other problems may develop.

Details

A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. The person may experience respiratory and circulatory problems due to the body's inability to maintain normal bodily functions. People in a coma often require extensive medical care to maintain their health and prevent complications such as pneumonia or blood clots. Coma patients exhibit a complete absence of wakefulness and are unable to consciously feel, speak or move. Comas can be derived by natural causes, or can be medically induced.

Clinically, a coma can be defined as the consistent inability to follow a one-step command. It can also be defined as a score of ≤ 8 on the Glasgow Coma Scale (GCS) lasting ≥ 6 hours. For a patient to maintain consciousness, the components of wakefulness and awareness must be maintained. Wakefulness describes the quantitative degree of consciousness, whereas awareness relates to the qualitative aspects of the functions mediated by the cortex, including cognitive abilities such as attention, sensory perception, explicit memory, language, the execution of tasks, temporal and spatial orientation and reality judgment. From a neurological perspective, consciousness is maintained by the activation of the cerebral cortex—the gray matter that forms the outer layer of the brain—and by the reticular activating system (RAS), a structure located within the brainstem.

Etymology

The term 'coma', from the Greek koma, meaning deep sleep, had already been used in the Hippocratic corpus (Epidemica) and later by Galen (second century AD). Subsequently, it was hardly used in the known literature up to the middle of the 17th century. The term is found again in Thomas Willis' (1621–1675) influential De anima brutorum (1672), where lethargy (pathological sleep), 'coma' (heavy sleeping), carus (deprivation of the senses) and apoplexy (into which carus could turn and which he localized in the white matter) are mentioned. The term carus is also derived from Greek, where it can be found in the roots of several words meaning soporific or sleepy. It can still be found in the root of the term 'carotid'. Thomas Sydenham (1624–89) mentioned the term 'coma' in several cases of fever (Sydenham, 1685).

Signs and symptoms

General symptoms of a person in a comatose state are:

* Inability to voluntarily open the eyes
* A non-existent sleep-wake cycle
* Lack of response to physical (painful) or verbal stimuli
* Depressed brainstem reflexes, such as pupils not responding to light
* Abnormal, difficulty, or irregular breathing or no breathing at all when coma was caused by cardiac arrest
* Scores between 3 and 8 on the Glasgow Coma Scale

Causes

Many types of problems can cause a coma. Forty percent of comatose states result from drug poisoning. Certain drug use under certain conditions can damage or weaken the synaptic functioning in the ascending reticular activating system (ARAS) and keep the system from properly functioning to arouse the brain. Secondary effects of drugs, which include abnormal heart rate and blood pressure, as well as abnormal breathing and sweating, may also indirectly harm the functioning of the ARAS and lead to a coma. Given that drug poisoning is the cause for a large portion of patients in a coma, hospitals first test all comatose patients by observing pupil size and eye movement, through the vestibular-ocular reflex.

The second most common cause of coma, which makes up about 25% of cases, is lack of oxygen, generally resulting from cardiac arrest. The Central Nervous System (CNS) requires a great deal of oxygen for its neurons. Oxygen deprivation in the brain, also known as hypoxia, causes sodium and calcium from outside of the neurons to decrease and intracellular calcium to increase, which harms neuron communication. Lack of oxygen in the brain also causes ATP exhaustion and cellular breakdown from cytoskeleton damage and nitric oxide production.

Twenty percent of comatose states result from an ischemic stroke, brain hemorrhage, or brain tumor. During a stroke, blood flow to part of the brain is restricted or blocked. An ischemic stroke, brain hemorrhage, or brain tumor may cause restriction of blood flow. Lack of blood to cells in the brain prevents oxygen from getting to the neurons, and consequently causes cells to become disrupted and die. As brain cells die, brain tissue continues to deteriorate, which may affect the functioning of the ARAS, causing unconsciousness and coma.

Comatose cases can also result from traumatic brain injury, excessive blood loss, malnutrition, hypothermia, hyperthermia, hyperammonemia, abnormal glucose levels, and many other biological disorders. Furthermore, studies show that 1 out of 8 patients with traumatic brain injury experience a comatose state.

Heart-related causes of coma include cardiac arrest, myocardial infarction, heart failure, arrhythmia when severe, cardiogenic shock, myocarditis, and pericarditis. Respiratory arrest is the only lung condition to cause coma, but many different lung conditions can cause decreased level of consciousness, but don't reach coma.

Other causes of coma include severe or persistent seizures, kidney failure, liver failure, hyperglycemia, hypoglycemia, and infections involving the brain, like meningitis and encephalitis.

Pathophysiology

Injury to either or both of the cerebral cortex or the reticular activating system (RAS) is sufficient to cause a person to enter coma.

The cerebral cortex is the outer layer of neural tissue of the cerebrum of the brain. The cerebral cortex is composed of gray matter which consists of the nuclei of neurons, whereas the inner portion of the cerebrum is composed of white matter and is composed of the axons of neuron. White matter is responsible for perception, relay of the sensory input via the thalamic pathway, and many other neurological functions, including complex thinking.

The RAS, on the other hand, is a more primitive structure in the brainstem which includes the reticular formation (RF). The RAS has two tracts, the ascending and descending tract. The ascending tract, or ascending reticular activating system (ARAS), is made up of a system of acetylcholine-producing neurons, and works to arouse and wake up the brain. Arousal of the brain begins from the RF, through the thalamus, and then finally to the cerebral cortex. Any impairment in ARAS functioning, a neuronal dysfunction, along the arousal pathway stated directly above, prevents the body from being aware of its surroundings. Without the arousal and consciousness centers, the body cannot awaken, remaining in a comatose state.

The severity and mode of onset of coma depends on the underlying cause. There are two main subdivisions of a coma: structural and diffuse neuronal. A structural cause, for example, is brought upon by a mechanical force that brings about cellular damage, such as physical pressure or a blockage in neural transmission. While a diffuse cause is limited to aberrations of cellular function, that fall under a metabolic or toxic subgroup. Toxin-induced comas are caused by extrinsic substances, whereas metabolic-induced comas are caused by intrinsic processes, such as body thermoregulation or ionic imbalances(e.g. sodium). For instance, severe hypoglycemia (low blood sugar) or hypercapnia (increased carbon dioxide levels in the blood) are examples of a metabolic diffuse neuronal dysfunction. Hypoglycemia or hypercapnia initially cause mild agitation and confusion, but progress 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.

Structural and diffuse causes of coma are not isolated from one another, as one can lead to the other in some situations. For instance, coma induced by a diffuse metabolic process, such as hypoglycemia, can result in a structural coma if it is not resolved. Another example is if cerebral edema, a diffuse dysfunction, leads to ischemia of the brainstem, a structural issue, due to the blockage of the circulation in the brain.

Diagnosis

Although diagnosis of coma is simple, investigating the underlying cause of onset can be rather challenging. As such, after gaining stabilization of the patient's airways, breathing and circulation (the basic ABCs) various diagnostic tests, such as physical examinations and imaging tools (CT scan, MRI, etc.) are employed to access the underlying cause of the coma.

When an unconscious person enters a hospital, the hospital utilizes a series of diagnostic steps to identify the cause of unconsciousness. According to Young, the following steps should be taken when dealing with a patient possibly in a coma:

* Perform a general examination and medical history check
* Make sure the patient is in an actual comatose state and is not in a locked-in state or experiencing psychogenic unresponsiveness. Patients with locked-in syndrome present with voluntary movement of their eyes, whereas patients with psychogenic comas demonstrate active resistance to passive opening of the eyelids, with the eyelids closing abruptly and completely when the lifted upper eyelid is released (rather than slowly, asymmetrically and incompletely as seen in comas due to organic causes).
* Find the site of the brain that may be causing coma (e.g., brainstem, back of brain...) and assess the severity of the coma with the Glasgow Coma Scale
* Take blood work to see if drugs were involved or if it was a result of hypoventilation/hyperventilation
* Check for levels of serum glucose, calcium, sodium, potassium, magnesium, phosphate, urea, and creatinine
* Perform brain scans to observe any abnormal brain functioning using either CT or MRI scans
* Continue to monitor brain waves and identify seizures of patient using EEGs.

Additional Information

Coma is a state of unconsciousness, characterized by loss of reaction to external stimuli and absence of spontaneous nervous activity, usually associated with injury to the cerebrum. Coma may accompany a number of metabolic disorders or physical injuries to the brain from disease or trauma.

Different patterns of coma depend on the origin of the injury. Concussions may cause losses of consciousness of short duration; in contrast, lack of oxygen (anoxia) may result in a coma that lasts for several weeks and is often fatal. Stroke, a rupture or blockage of vessels supplying blood to the brain, can cause sudden loss of consciousness in some patients, while comas caused by metabolic abnormalities or cerebral tumours are characterized by a more gradual onset, with stages of lethargy and stupor before true coma. Metabolic comas are also more likely to have associated brain seizures and usually leave pupillary light reflexes intact, whereas comas with physical causes usually eradicate this reflex.

Common causes of metabolic coma include diabetes, excessive consumption of alcohol, and barbiturate poisoning. In diabetes, low insulin levels allow the buildup of ketones, breakdown products of fat tissue that destroy the osmotic balance in the brain, damaging brain cells. Ingestion of large quantities of alcohol over a short period can cause a coma that may be treated by gastric lavage (stomach pump) in its early stages; alcohol combined with barbiturates is a common cause of coma in suicide attempts. Large doses of barbiturates alone will also produce coma by suppressing cerebral blood flow, thus causing anoxia. Gastric lavage soon after the drug is ingested may remove a sufficient amount of the barbiturate to allow recovery.

For most metabolic comas, the first step in treatment is to protect the brain cells and attempt to eliminate the cause of coma. Assisted ventilation is often necessary. In some psychiatric conditions, such as catatonic schizophrenia, a comalike state may also occur. Electroencephalography (EEG) can be used to detect signs of consciousness in patients who are unresponsive; research suggests that EEG recordings potentially can be used to predict whether a patient will emerge from coma.

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#1 2023-12-10 21:44:26

Coma

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