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Overview
A coma is a deep state of
unconsciousness, during which an individual is not
able to react to their environment. Someone in a
coma cannot respond to any form of stimulation
whatsoever. Coma can be caused by an underlying
illness, or it can result from head trauma. A
comatose person is still very much alive, but he
or she is not simply asleep. The brain wave
activity in a comatose person is very different
from that of a sleeping person; you can wake up a
sleeping person, you can't wake a person in a
coma. A coma usually does not last for more than a
few weeks. Many people recover their full physical
and mental functioning when they emerge from a
coma. Others require various forms of therapy to
recover as much functioning as possible. Some
patients never recover anything but very basic
body functions.
Sometimes, following a coma, a
person may enter what is known as a persistent
vegetative state; patients in persistent
vegetative state have lost all cognitive
neurological function but are still able to
breathe and may exhibit various spontaneous
movements. They may even be awake and appear to be
normal but, because the cognitive part of their
brain no longer functions, they are not able to
respond to their environment. A vegetative state
can last for years.
There are various other terms, in
addition to coma and vegetative state, that are
used to describe varying levels of unconsciousness
and a person's ability to respond to stimuli.
These include stupor, in which a person is
unconscious but will eventually respond to
repeated, vigorous stimulation; and obtundation
and lethargy, which are used to describe a person
who is not entirely unconscious but does not
respond to stimuli.
Usually, coma and other altered
states of unconsciousness are considered
neurological emergencies, and actions need to be
taken quickly to avoid permanent damage.
The Human Brain
The human brain is made up of three basic parts:
the cerebrum, the cerebellum, and the brainstem.
The cerebrum is the largest part of the brain and
makes up about 85% of the brain's total weight.
It's divided into two hemispheres, the cerebral
hemispheres, one on each side of the head. The
cerebrum is where all of the body's most
complicated mental and sensory functions are
controlled - intelligence, reasoning, memory,
emotions, vision, our ability to feel things, etc.
The cerebellum is a smaller part of the brain that
lies behind the cerebrum. It plays an essential
role in coordination, posture and balance. The
brainstem is the stemlike part of the brain that
connects the cerebral hemispheres to the spinal
cord and is responsible for controlling many basic
bodily functions, such as breathing, blood
pressure, and being awake and alert.
Unconsciousness
As with most mental processes that occur in the
brain, the biology of consciousness - also called
arousal - is very complicated and not well
understood. There are many tissues located deep
within the brain that play a role in how conscious
and alert a person is. Researchers believe that
one of the important physiological processes that
keeps a person conscious is the transfer, or
neurotransmission, of chemical signals from the
brainstem to the cerebral hemispheres of the
brain. This continuous neurotransmission needs to
be happening in order for a person to be aware of
their environment. Abnormalities that interrupt it
can lead to coma or other states of
unconsciousness.
Abnormalities that can cause coma
include injury or damage to the brain that leads
to swelling (edema) in the brain, which results in
an increased intracranial pressure (pressure
within the skull). Increased pressure, whether it
is localized in one particular spot or spread over
the whole brain, decreases the flow of blood and
can lead to unconsciousness. Injury or damage to
the brain can also cause some areas of the brain
to shift within the skull and exert pressure on
surrounding tissues and structures, including
blood vessels. When a part of the brain shifts
position like this, the event is called a brain
herniation, and it can lead to coma and death if
not treated immediately.
Symptoms
All the various states of
unconsciousness are themselves symptoms of severe
neurological dysfunction. Coma can begin suddenly,
such as when a person suffers a brain hemorrhage
or severe head trauma, or coma can develop slowly
over time. In a person who is intoxicated with
alcohol or other drugs, for example, the early
signs of an impending state of unconsciousness
develop slowly as the person consumes more.
Usually the progression of the state of
unconsciousness and how quickly it develops,
provides clues about what is causing it.
In a slowly developing coma,
patients may be only mildly confused and drowsy in
the beginning, and/or their personality may
change. If the underlying cause is an infection in
the central nervous system, patients may feel a
headache or other bodily discomfort, a fever,
rash, muscular pains, or dizziness, before the
actual coma develops. As time passes, they may
begin to show signs of lethargy and obtundation,
during which they are not quite unconscious but
are not responding to external stimuli.
Sometimes a person who is falling
into unconsciousness may not recognize what is
happening and may not be able to complain. Or, it
may happen so quickly that they don't have time to
notice and complain.
After a person has entered into a
state of unconsciousness, they tend not to respond
to external stimuli, depending on how deep the
coma is, and/or they show abnormal body movements.
An unconscious person may lie still and not
respond to anything. They may move spontaneously;
these movements include shaking, tremors, and
jerking movements. The eyes may move abnormally.
If the breathing muscles are affected, a person's
breathing may be irregular, and they may need to
be put on a respirator.
Causes
There are many things that can
cause coma or other states of unconsciousness.
Some of the causes are treatable and reversible,
and others are not. Some of them are focal
processes - localized abnormalities that exist
only in one part of the brain; others are diffuse
processes that affect large parts of the brain.
Focal Processes
Focal processes that are localized to a specific
spot in the brain and can lead to coma include:
brain hemorrhage, an abnormal flow of blood that
occurs in a specific place in the brain; ischemic
stroke, a stroke due to the obstruction of a blood
vessel in the brain; a brain tumor; and brain
abscesses, infections in the brain.
Diffuse Processes
Diffuse processes that are widespread and affect
large parts of the brain include: head trauma
associated with an increased intracranial
pressure; various toxins, including poisons,
alcohol and other drugs that can lead to coma
including barbiturates, opiate narcotics,
sedatives, amphetamines, cocaine, and aspirin;
metabolic abnormalities that lead to either
elevated or reduced glucose levels in the blood;
liver or kidney failure; hypoxia (poor
oxygenation) or an imbalance of electrolytes, the
substances like salts that are found in the blood
and tissues and play essential roles in normal
body function; central nervous system infections,
such as meningitis and encephalitis; a hemorrhage
in one of the membranous layers covering the
brain; seizure disorders; and extreme elevation in
blood pressure.
Psychiatric Causes
Sometimes, it is difficult to know if a person's
unresponsiveness is due to psychiatric problems
rather than a medical illnesses.
Diagnosis
Medical History
As with most neurological problems, the first step
in diagnosing what is causing a coma or other
state of unconsciousness is to obtain a complete
medical history. Obviously, there is no way to get
this information from the comatose patient, so
physicians must rely on friends and family for
these details. It is important to know how the
coma developed, whether it was sudden or slow. It
is also helpful to know about any medical problems
that the comatose person has, including diabetes
mellitus, high blood pressure, kidney disease,
liver disorders, or a history of seizures.
Physical Exam & Neurological
Evaluation
The physical exam will evaluate a comatose
person's breathing pattern and cardiovascular
function, as well as look at the skin and limbs
for any noticeable abnormalities. Sometimes,
particular breathing patterns are related to
specific abnormalities in the brain, and they can
be used to identify the underlying problem.
Eye Examination
The eyes will be examined carefully. Like a
person's breathing pattern, the way the eye moves
is sometimes related to specific abnormalities in
the brain and can be used to identify the
underlying problem. A fundoscope is used to
examine the optic nerve in the back of the eye for
any signs of swelling, which indicates that there
may be increased intracranial pressure.
Laboratory Tests
Usually, a full set of laboratory tests are done
on the comatose patient. These include blood tests
that check the liver, kidney and thyroid function,
glucose levels, and the presence of any toxins.
The results of the various lab tests may provide
clues as to what has caused the coma.
Imaging Studies
A CT
(computerized axial tomography)
and MRI (magnetic resonance imaging) can
both be used to visualize most abnormalities in
the brain. In some cases, a lumbar puncture, known
as a spinal tap, may be done to remove some of the
cerebrospinal fluid for evaluation.
EEG
If a seizure is suspected, an
electroencephalography (EEG) can be done to
confirm it or rule it out. An EEG tests the
electrical activity in the brain.
Treatment
Patients who are unresponsive
require immediate treatment in order to avoid
serious consequences.
The "Coma Cocktail"
Although the treatment of coma depends on the
cause, there are some general treatment rules. If
the cause is unknown, what is often called a "coma
cocktail" is given to the patient. It's a mixture
of thiamin (a vitamin that can help in alcoholic
or nutritionally starved patients), glucose (a
sugar that can help diabetics who have developed a
coma due to low sugar level), and naloxene (a
substance that reverses the action of many
narcotics and is used to treat overdoses).
Correcting for Electrolyte
Imbalance or Toxic Substances
Electrolytes are chemicals like salts, such as
sodium and chlorine salts, that are found in the
blood and tissues throughout the body and play an
essential role in most physiological processes.
Depending on what has caused the coma, it may be
necessary to correct any electrolyte
abnormalities. A renal dialysis, for example, is a
process that removes toxins and maintains normal
electrolyte balance in the kidneys.
Decreasing Intracranial Pressure
If the coma is related to increased pressure in
the brain, there are various things that can be
done to reduce it, including hyperventilation,
diuretics and surgery. Hyperventilation involves
increasing the rate and depth of breathing so that
the blood vessels in the brain constrict and the
blood flow slows down, which can decrease the
brain pressure. Diuretics, also known as fluid
pills, can decrease brain pressure by removing
excess fluid in the brain. If there is an
accumulation of fluid in the ventricles, known as
hydrocephalus, surgery can remove excess fluid,
which can also decrease the intracranial pressure.
Other Treatments
It may be necessary to prescribe medications to
treat seizures. If the coma is caused by an
infection, antibiotics will be prescribed.
Most comatose patients are not able
to breathe on their own and need to be put on a
respirator. Some patients also need cardiovascular
support, hydration, and some form of nutrition.
Sometimes physical therapy is used
to prevent skeletal or muscular deformities that
may develop in people who come out of a coma.
Treatment of Long-term Coma and
Persistent Vegetative State
Some people do not immediately come out of coma
despite having been treated for the suspected
underlying cause. In such cases, treatment focuses
on preventing infections such as pneumonia,
maintaining the patient's physical state
(preventing bed sores, for example), and providing
adequate nutrition. This is true for people in
persistent vegetative state as well, for whom
pneumonia is the most common cause of death.
Prognosis
The prognosis, whether or not a person will come
out of coma, depends on what causes the coma. If
it's caused by reversible metabolic processes and
is treated rapidly, patients tend to recover very
well. If it's caused by massive bleeding in the
brain or large brain tumors, however, most
patients do not recover. |
