The National Institute of Neurological Disorders and Stroke defines a coma as "a profound or deep state of unconsciousness." A patient may fall into a coma due to mild, moderate or severe brain damage. Accidents involving traumatic brain injury are one of the most common causes of comas. A coma that lasts longer than four weeks is reclassified as a persistent vegetative state, a more serious loss of consciousness.
Causes of Coma
Comas can be caused by several medical complications and conditions, including:
- Traumatic brain injury
- Diabetes (hypoglycemic coma)
- Lack of oxygen
- Toxic exposure
One of the most common causes of coma is traumatic brain injury, which often occurs during assaults and transportation accidents. A traumatic brain injury may be classified as either an open head injury or a closed head injury and can cause focal brain damage, which affects isolated sections of the brain, or diffuse brain damage, which affects a broader area. Focal and diffuse brain damage can influence consciousness, as well as cause intracranial pressure or swelling.
In addition to those suffering from traumatic brain injury, diabetic patients are at risk for coma from extreme levels of blood sugar. Conditions that block blood flow and lead to a lack of oxygen, such as hemorrhaging or stroke, can also cause patients to fall into a comatose state.
Even healthy individuals can fall into a coma if they are exposed to certain environmental factors. This includes infections, such as encephalitis and meningitis, and toxic poisoning, which can be caused by exposure to carbon monoxide and other toxins.
One of the most obvious symptoms of a coma is a lack of consciousness. The onset of a coma can be gradual or immediate, depending on the cause. Patients who suffer from mild traumatic brain injuries may experience headaches, drowsiness, confusion, body aches, fever and dizziness before falling into a coma.
Patients in a coma lack awareness and wakefulness, which means they do not respond to external stimuli or pain. Although they may demonstrate reflexive movements, patients who do not exhibit purposeful movements are deemed unconscious. Comatose patients also keep their eyes closed, have impaired breathing and fail to exhibit a normal sleep-wake pattern.
Physical & Neurological Evaluation
Doctors use physical examinations as well as medical technologies to evaluate head injuries and diagnose comas. Once they have treated open wounds and established proper breathing and blood flow to the brain, they evaluate a patient's medical history to check for medications, conditions such as diabetes, and medical events such as strokes. Then, they check a patient's reflexes and pupil size to determine the level of consciousness. Doctors also take a blood sample to test blood count, electrolytes, and glucose levels, and look for any remnants of drugs or toxins such as carbon monoxide.
Once the physical evaluation is complete, several neurological examinations are performed. A patient's level of consciousness is assessed using the Glasgow Coma Scale or the Rancho Los Amigos Scale. These scales also help doctors evaluate a patient's chance of recovery.
X-Rays and Imaging
Medical technologies allow doctors to identify the location and severity of the injury sustained. CT scans, MRI scans and EEG tests check for hemorrhaging, swelling, brain stem damage and non-convulsive seizures, an underlying cause of comas. In addition, they allow doctors to identify the level of consciousness and create appropriate treatment plans.
Patients in a coma are at risk for a variety of complications. One of the most serious is progression into a persistent vegetative state. A coma lasting longer than two to four weeks is reclassified as a persistent vegetative state. Patients who fall into a persistent vegetative state typically have much lower chances of recovery.
Doctors always monitor comatose patients for any secondary brain injuries caused by brain swelling or intracranial pressure.
Due to inactivity, patients in a coma may experience bed sores, or skeletal or muscular atrophy. These complications can be overcome with appropriate rehabilitation plans.
In order to successfully treat comatose patients, doctors must prevent secondary brain injuries from causing further damage, such as swelling and intracranial pressure.
Reducing Intracranial Pressure
To reduce intracranial pressure, doctors can prescribe medication or recommend surgery. A craniotomy may be performed to relieve pressure; this procedure creates holes in the skull to allow for excess blood and fluid to drain. Alternatively, the surgeon may insert a catheter to relieve pressure or remove a portion of the skull to create room for brain swelling.
Other Coma Treatments
Upon admission to a hospital, patients often receive antibiotics or glucose to treat suspected infections or diabetic comas. Doctors may also administer strong medications to control patients who suffer from non-convulsive seizures.
Because there is no cure for a coma, treatment options are limited to preventing further damage, treating underlying causes and maintaining proper blood flow and nutrition.
A patient's chance of recovery is dependent on the severity of the personal injury sustained and the amount of time spent in a comatose state. Patients with mild head injuries often regain consciousness within a few weeks. Those with severe brain damage may slip into persistent vegetative states.
Patients who regain consciousness usually regain their cognitive and motor skills after rehabilitation. Through these programs, physical therapists and doctors help patients in their effort to recover the skills necessary to live independently.
To learn more about traumatic brain injury, or other states of consciousness associated with head injury, please refer to other articles on this site.
[Last revision: January 2010]