How fast a person comes out of a coma depends on what caused it and the severity of the damage to the brain. If the cause was a metabolic problem such as diabetes, and doctors treat it with medication, he or she can come out of the coma relatively quickly. Many patients who overdose on drugs or alcohol also can recover once the substance clears their system. A massive brain injury or brain tumor can be more difficult to treat, and can lead to a much longer or irreversible coma.
Most comas don't last more than two to 4 weeks. Recovery is usually gradual, with patients becoming more and more aware over time. They may be awake and alert for only a few minutes the first day, but gradually stay awake for longer and longer periods. Research shows that a comatose patient's outcome relates very closely to his or her Glasgow Coma Scale score. The majority of people (87 percent) who score a three or a four on the scale within the first 24 hours of going into a coma are likely to either die or remain in a vegetative state. On the other end of the scale, about 87 percent of those who score between 11 and 15 are likely to make a good recovery.
Some people come out of a coma without any mental or physical disability, but most require at least some type of therapy to regain mental and physical skills. They may need to relearn how to speak, walk, and even eat. Others are never able to recover completely. They may regain some functions (such as breathing and digestion) and transition into a vegetative state, but will never respond to stimuli.
The brain is made up of three major parts: the cerebrum, the cerebellum and the brain stem. The cerebrum is the largest part of the brain. It makes up most of the total brain. The cerebrum controls cognitive and sensory functions such as intelligence, memory, reasoning and emotions. The cerebellum in the back of the brain controls balance and movement. The brain stem connects the two hemispheres of the cerebrum to the spinal cord. It controls breathing, blood pressure, sleep cycles, consciousness and other body functions. In addition, there is a large mass of neurons beneath the cerebrum, called the thalamus. This small, but critical area relays sensory impulses to the cerebral cortex. For a more detailed explanation of the brain's function, see How Your Brain Works.
Scientists believe that consciousness depends on the constant transmission of chemical signals from the brainstem and thalamus to the cerebrum. These areas are connected by neural pathways called theReticular Activating System (RAS). Any interruptions to these messages can put someone into an altered state of consciousness.
A vegetative state is a type of coma that represents an awake but unresponsive state of consciousness. Many of these patients were comatose previously and after a few days or weeks emerge to an unconscious state in which their eyelids are open, giving the impression that they are awake. Patients in this state of consciousness may exhibit behaviors that lead family members to incorrectly believe they are becoming awake and communicative. These behaviors can include grunting, yawning and moving the head and limbs. However, these patients do not actually respond to any internal or external stimuli and evidence of extensive brain damage still persists. The outcome of patients in whom a vegetative state lasts for a month or more is generally poor and doctors use the term persistent vegetative state.
How does someone become Comatose?
Illnesses that affect the brain and brain injuries can both cause comas. If a person suffers severe head trauma, the impact can cause the brain to move back and forth inside the skull. The movement of the brain inside the skull can tear blood vessels and nerve fibers, which causes swelling in the brain. This swelling presses down on blood vessels, blocking the flow of blood (and with it, oxygen) to the brain. The oxygen- and blood-starved parts of the brain begin to die. Some infections of the brain and spinal cord (such as encephalitis or meningitis) can also cause swelling in the brain. Conditions that cause an excess of blood inside the brain or skull, such a skull fracture or a burst aneurysm, can also lead to swelling and further brain injury.
A type of stroke, called an ischemic stroke, can also lead to a coma. This stroke occurs when an artery that supplies the brain with blood is blocked. The blockage starves the brain of blood and oxygen. If it is very large, the person can fall into a stupor or coma. In people with diabetes, the body does not produce enough of the hormone insulin. Because insulin helps cells use glucose for energy, a lack of the hormone causes blood glucose levels to rise (hyperglycemia).
Conversely, when insulin isn't in the right proportion, blood sugar can drop too low (hypoglycemia). If the blood sugar is either extremely high or low, it can cause a person to fall into adiabetic coma. Comas can also be caused by brain tumors, alcohol or drug overdoses, seizure disorders, lack of oxygen to the brain (such as from drowning) or extremely high blood pressure.
A person can become comatose immediately or gradually. If an infection or other illness causes the coma, for example, the person might run a high fever, feel dizzy or seem lethargic before falling into a coma. If the cause is a stroke or severe head trauma, they can become comatose almost immediately.
(Source - Various Science Journals)
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