What is a "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.

What is the Glasgow Coma Scale?

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.

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

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.

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.

What are the 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.

Picture of the brain and potentially brain injury areas

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.

Hypoglycemic coma

All cells in the body need glucose and oxygen to perform their functions by aerobic metabolism (aerobic= with oxygen). While other parts of the body can continue for short periods of time anaerobically (an=without + aerobic+oxygen), the brain cannot. Without glucose, the brain stops.

Hypoglycemia (hypo=low + glyc=glucose + emia= blood) most often occurs in people with diabetes who have given themselves too much insulin or have not taken in enough food.

In normal physiology, the pancreas makes insulin and balances the amount it produces with the amount of glucose in the blood stream. Diabetics need to inject insulin into their body, or take medication to stimulate the pancreas to make insulin. Monitoring blood sugars is critical to avoid hypoglycemic coma.

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.

How is coma assessed?

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.

What tests are there 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.

What is the 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.

sourceLast Editorial Review: 11/21/2007

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