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Definition of "coma"

Coma is a state of unconsciousness whereby a patient cannot react with the surrounding environment. The patient cannot be wakened with outside physical or auditory stimulation. The inability to waken differentiates coma from sleep. Patients can have different levels of unconsciousness and unresponsiveness depending upon how much or how little of the brain is functioning.

Measuring the depth of coma

The Glasgow Coma Scale was developed to provide health-caregivers a simple way of measuring the depth of coma based upon observations of eye opening, speech, and movement. Patients in the deepest level of coma:

- Do not respond with any body movement to pain,
- Do not have any speech, and
- Do not open their eyes.

Those in lighter comas may offer some response, to the point they may even seem wake, yet meet the criteria of coma because they do not respond to their environment.

The scale is used as part of the initial evaluation of a patient, but does not assist in making the diagnosis as to the cause of coma. Since it "scores" the level of coma, the GCS can be used as a standard method for any health-caregiver to assess change in patient status.

Glasgow Coma Scale:
Eye Opening
Spontaneous 4
To loud voice 3
To pain 2
None 1

Verbal Response
Oriented 5
Confused, Disoriented 4
Inappropriate words 3
Incomprehensible words 2
None 1

Motor Response
Obeys commands 6
Localizes pain 5
Withdraws from pain 4
Abnormal flexion posturing 3
Extensor posturing 2
None 1

Interpretation to GCS
Individual elements as well as the sum of the score are important. Hence, the score is expressed in the form "GCS 9 = E2 V4 M3 at 07:35".

Generally, brain injury is classified as:
Severe, with GCS ≤ 8
Moderate, GCS 9 - 12
Minor, GCS ≥ 13.

Tracheal intubation and severe facial/eye swelling or damage make it impossible to test the verbal and eye responses. In these circumstances, the score is given as 1 with a modifier attached e.g. 'E1c' where 'c' = closed, or 'V1t' where t = tube. A composite might be 'GCS 5tc'. This would mean, for example, eyes closed because of swelling = 1, intubated = 1, leaving a motor score of 3 for 'abnormal flexion'. Often the 1 is left out, so the scale reads Ec or Vt.

The GCS has limited applicability to children, especially below the age of 36 months (where the verbal performance of even a healthy child would be expected to be poor). Consequently the Pediatric Glasgow Coma Scale, a separate yet closely related scale, was developed for assessing younger children.

Pediatric Glasgow Coma Scale




























There are many causes of coma, but to understand unconsciousness, we need to know why a person is awake. The brain is a large organ with many parts. There are two main portions when separated down the middle (right and left cerebral hemispheres) containing the frontal, parietal, temporal and occipital lobes, where movement, sensation, speech and thought are housed. The cerebellum sits under the cerebral hemispheres and is where balance and coordination are located. The brain stem is where automatic responses to the body including heart rate, blood pressure, and breathing are controlled. The reticular activating system (RAS) is located within the brain stem and is the important "on/off" switch of the brain.

To be awake, the reticular activating system (RAS) must be functioning, as well as at least one cerebral hemisphere.

If a person loses consciousness, either the RAS has stopped working, or both cerebral hemispheres have shut down.

The reticular activating system stops working in two situations:
1. Brain stem stroke: cells in that area of the brain stem have lost oxygen and glucose supplied by blood flow, then function stops. This is either ischemic (where blood supply is lost) or hemorrhagic (where bleeding occurs and the structures fail).

2. A pre-death event: increased swelling in the brain pushes down on the brain stem and causes it to fail. To have both cerebral hemispheres fail requires the blood supply to the brain be compromised, or some sort of toxic insult has occurred to all brain tissue.

Causes of Coma

Generally, coma is commonly a result of trauma, bleeding and/or swelling affecting the brain. Inadequate oxygen or blood sugar (glucose) and various poisons can also directly injure the brain to cause coma.

Trauma
Minor head injuries can cause brief loss of consciousness, but the brain is able to turn itself back on. Similarly, patients with seizures become unconscious - but gradually waken relatively quickly. Those people who cannot respond after head injury usually have had significant force applied to their head and brain.

The skull is a rigid box that protects the brain. Unfortunately, if the brain is injured and begins to swell (edema), there is no room for the additional fluid. This causes the brain to push up against the sides of the skull and it then compresses. Unless the pressure is relieved, the brain will continue to swell until it pushes down onto the brain steam, which then damages the RAS, which subsequently affects blood pressure and breathing control centers.

The affect of trauma on the brain is not predictable. It may or may not cause significant injury. If the brain is shaken, shear injury may occur, where the nerve connections within the brain are damaged. Coma may occur even with a normal CT scan in this situation. Similarly, head trauma may cause swelling of the brain without any bleeding, and coma may be the result.

Head trauma can cause different types of brain injury. The injury can occur to the brain tissue itself or may cause bleeding to occur between the brain and the skull. Computerized Tomography (CT) of the head can identify most bleeding from trauma.

Bleeding (Hemorrhage)
Intracerebral hemorrhage (intra= within + cerebral=brain + hemorrhage=bleeding) may be small, but it is associated swelling that may cause damage.

Epidural, subdural, and subarachnoid hemorrhages
The lining of the brain has multiple layers, and these layers can act as potential spaces where bleeding can occur. Epidural (epi= outside the dura= an outer layer of brain lining) and subdural (sub=below the dura) may not cause coma immediately, but as the bleeding continues, it compresses the injured side of the brain and shifts it to the unaffected side. Now both cerebral hemispheres are affected and loss of consciousness or coma may occur; the more swelling, the deeper the coma.

Subarachnoid hemorrhage (below the arachnoid layer) is in the layer of the brain lining where cerebrospinal fluid (CSF) is. CSF is the nutrient fluid that bathes the brain and spinal cord. Bleeding here may be without symptoms or it may cause significant problems, such as paralysis.

Bleeding can occur within the skull or brain without trauma. Blood accumulating in areas it should not b,e result with the same problem. Some medical causes include:

Hypertension (high blood pressure): when blood pressure is too high, and not controlled, blood vessels in the brain may not be able to tolerate the high pressure and may leak blood.

Cerebral aneurysm, or an area in a blood vessel that is congenitally weak and ruptures. Some people are born with blood vessels that have a weak wall and it gradually balloons, like a weak spot in an inner tube. At some time in their life, or perhaps never, the weak spot gives way and blood is spilled into the brain.

Arteriovenous malformations (AVMs) are abnormal blood vessels where arteries connect to veins and cause potential weak spots that can leak blood. Normally, arteries branch into smaller and smaller vessels until they form the smallest set of vessels called capillaries. Capillaries form meshes where chemicals, nutrients, oxygen and carbon dioxide are exchanged from the blood stream to individual cells. The capillaries then merge to form larger blood vessels, the veins. In AVMs, this relationship of artery to capillary to vein is abnormal.

Tumors, either benign or malignant, can be very vascular (composed of many veins and capillaries) and have significant bleeding potential.

Swelling
While trauma can make the brain swell, other types of injury or insult can cause cerebral edema (cerebral=brain + edema=swelling due to increased fluid). Whether the insult is lack of oxygen, abnormal electrolytes, or hormones, it may ultimately result in edema of the brain tissue. As with bleeding, the skull limits the space available for brain swelling to occur; thus the brain tissue is damaged and its function decreases the more it is compressed against the bones of the skull.

Lack of oxygen
The brain requires oxygen to function; and without it the brain shuts down. There is a very short time to get oxygen back to brain tissue before there is permanent damage. Most research suggests that the time window is four to six minutes.

The body provides oxygen to the brain through the lungs. The lungs extract oxygen from the air, hemoglobin in red blood cells pick up the oxygen, and the heart pumps blood through normal blood vessels to cells in the body. If any part of the system fails, the oxygen supply to the brain can be interrupted.

The most common failure occurs with heart rhythm disturbances. The coordinated electrical beat of the heart is lost and the heart muscle doesn't squeeze blood adequately; no blood is pumped to the brain and it stops functioning almost immediately.

Lungs can also fail; examples include pneumonia, emphysema, or asthma. In each case, inflammation in the lung tubes (bronchi or bronchioles) or lung tissue makes it difficult for oxygen to get into the lungs and transferred into the blood stream.

Hemoglobin, a molecule in the red blood cell, attaches oxygen from the lungs and delivers it to cells for use in metabolism. Anemia, or low red blood cell count, can cause the brain to fail directly, or more likely it causes other organs like the heart to fail. The heart, like any other muscle requires oxygen to function. Anemia can occur chronically or it can be due to an acute blood loss (examples include trauma, bleeding from the stomach). If the blood loss is slow, the body is better able to adapt and tolerate low hemoglobin levels; if the bleeding occurs quickly, the body may be unable to compensate, the result being inadequate oxygen supply to tissues such as the brain.

Diabetic coma
Severe hypoglycemia
People with type 1 diabetes mellitus who must take insulin in full replacement doses are most vulnerable to episodes of hypoglycemia. It is usually mild enough to reverse by eating or drinking carbohydrates, but blood glucose occasionally can fall fast enough and low enough to produce unconsciousness before hypoglycemia can be recognized and reversed. Hypoglycemia can be severe enough to cause unconsciousness during sleep. Predisposing factors can include eating less than usual, prolonged exercise earlier in the day, and heavy drinking. Some people with diabetes can lose their ability to recognize the symptoms of early hypoglycemia.

Unconsciousness due to hypoglycemia can occur within 20 minutes to an hour after early symptoms and is not usually preceded by other illness or symptoms. Twitching or convulsions may occur. A person unconscious from hypoglycemia is usually pale, has a rapid heart beat, and is soaked in sweat: all signs of the adrenaline response to hypoglycemia. The individual is not usually dehydrated and breathing is normal or shallow. A meter or laboratory glucose measurement at the time of discovery is usually low, but not always severely, and in some cases may have already risen from the nadir that triggered the unconsciousness.

Unconsciousness due to hypoglycemia is treated by raising the blood glucose with intravenous glucose or injected glucagon.

Advanced diabetic ketoacidosis
Diabetic ketoacidosis (DKA), if it progresses and worsens without treatment, can eventually cause unconsciousness, from a combination of severe hyperglycemia, dehydration and shock, and exhaustion. Coma only occurs at an advanced stage, usually after 36 hours or more of worsening vomiting and hyperventilation.

In the early to middle stages of ketoacidosis, patients are typically flushed and breathing rapidly and deeply, but visible dehydration, pallor from diminished perfusion, shallower breathing, and rapid heart rate are often present when coma is reached. However these features are variable and not always as described.

If the patient is known to have diabetes, the diagnosis of DKA is usually suspected from the appearance and a history of 1–2 days of vomiting. The diagnosis is confirmed when the usual blood chemistries in the emergency department reveal hyperglycemia and severe metabolic acidosis.

Treatment of DKA consists of isotonic fluids to rapidly stabilize the circulation, continued intravenous saline with potassium and other electrolytes to replace deficits, insulin to reverse the ketoacidosis, and careful monitoring for complications.

Nonketotic hyperosmolar coma
Nonketotic hyperosmolar coma usually develops more insidiously than DKA because the principal symptom is lethargy progressing to obtundation, rather than vomiting and an obvious illness. Extreme hyperglycemia is accompanied by dehydration due to inadequate fluid intake. Coma from NKHC occurs most often in patients who develop type 2 or steroid diabetes and have an impaired ability to recognize thirst and drink. It is classically a nursing home condition but can occur in all ages.

The diagnosis is usually discovered when a chemistry screen performed because of obtundation reveals extreme hyperglycemia (often above 1800 mg/dl (100 mM)) and dehydration. The treatment consists of insulin and gradual rehydration with intravenous fluids.

Poisons
There are two sources of poisons that can affect the brain, those that we take in (through ingestion or inhaling) and those that the body generates and cannot dispose of in some way.

If the body can be considered a factory, it needs to have the ability to get rid of the waste products that are made when the body generates energy. These waste products can cause different organs in the body to fail, including the brain.

The liver performs many functions including glucose and protein manufacturing. It also breaks down and metabolizes chemicals in the body. When the liver fails different chemicals like ammonia can accumulate and can cause brain cells to stop functioning. Hepatic encephalopathy (hepatic=liver + encephalo=brain + pathy=disease) or hepatic coma occurs when the liver fails because of an acute or chronic injury. The most common is cirrhosis due to alcoholism.

The kidneys filter blood to rid the body of waste products. When the kidneys fail, a variety of waste products can accumulate in the bloodstream and cause direct or indirect damage to the brain. An example of indirect causes would be an elevated potassium level affecting heart electrical activity. Direct causes include uremia, where blood urea levels rise and are directly toxic to brain cells. Common causes of kidney failure include poorly controlled diabetes and high blood pressure.

The thyroid acts as the thermostat for the body and regulates the speed at which the body functions. If thyroid levels drop too low, gradually, over a period of time myxedema coma can occur because of profound hypothyroidism.

Ingestions can cause the brain to slow down, speed up or alter its perception of the world. Some ingestions may cause coma in an indirect way. Acetaminophen is a prime example, an overdose may cause the liver to fail and few days later subsequent hepatic coma occurs.

Alcohol is probably the most common cause of ingested poison or toxin, leading to altered mental status and coma. In acute alcohol intoxication, the brain is directly poisoned. Blood alcohol levels fall when metabolized by the liver, but depth of intoxication can be so great it shuts off many of the involuntary brain activities that control breathing and maintain muscle function. Opiates like pain pills or heroin can cause similar slowing of brain function.

Cocaine and amphetamines are the common "uppers" or brain stimulants. These brain stimulants cause an adrenaline-like body response, thus blood pressure and heart rate spiral out of control and the risk of heart attack, heart rhythm disturbances, or bleeding in the brain occur.

Assessing coma

When a patient presents in coma, diagnosis and treatment begin simultaneously. Initial treatment is aimed at addressing immediate life-threatening issues:

Are the ABCs intact? Is the patient's airway open? Are they breathing? Do they have good circulation (a heart beat and blood pressure)?

Is the patient hypoglycemic? The blood sugar is checked by a quick fingerstick bedside test and if it is low, glucose is administered.

Did the patient ingest a narcotic? Naloxone (Narcan) may be given intravenously to reverse an overdose situation.
History remains the important key to the diagnosis. Since the patient cannot be the source of information, questions are asked of family, friends, bystanders, and rescue personnel. For example, a person sitting at a bar fell down, hit his head and is in coma. While it might be easy to jump to the conclusion that he was intoxicated, fell, and bled in his brain, other scenarios need to be considered. Did he have a heart attack, did he suffer a stroke, or was this a diabetic medication reaction and the blood sugar is low.

Once the patient has been stabilized with acceptable vital signs, physical examination will include a complete neurologic assessment. From head to toe, this may include examination of the eyes, pupils, face movements to assess cranial nerves including facial movement and gag reflex, extremity movement and reaction to stimulation, tendon reflexes and other testing of spinal cord function. There is special attention paid to symmetry in the neurology exam, since lack of movement or response on one side of the body may be caused by bleeding inside the skull or by stroke. General examination surveys the skin for cuts, scrapes, wounds, etc.

The GCS score will be documented; the deeper the coma, the lower the score. Please appreciate that a person with a "normal" GCS of 15 still can be in coma. Once the initial screening physical examination complete, a more detailed exam will likely occur to include the lungs, the heart, and the abdomen. Repeated neurologic assessment is key to monitoring the status of the patient and decide if the coma is lightening or getting worse.

Tests for coma

The strategy to decide which tests will help provide a diagnosis will depend upon the suspected cause. Many times, the cause involves many factors and the sequence of events will require serious detective work. Blood tests, electrocardiogram and CT scan of the head are most often obtained.

Outcome and prognosis for a patient in a coma

Depending upon the diagnosis, the evaluation may be no more than assessing blood sugar, treating hypoglycemia, and having complete resolution of the situation. On the other hand, the cause of coma may be a catastrophic brain hemorrhage without hope for significant recovery. The outlook very much depends on the cause of the coma and the ability to correct the particular situation.