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Loss Of Consciousness

Loss Of Consciousness

Alternate Names

  • unconsciousness


Consciousness is the state of being aware of or responsive to the environment. A person who is conscious can perceive, both physically and mentally, what is happening. An individual can lose consciousness for any of a number of reasons.

What is going on in the body?

An unconscious person generally seems to be sleeping. However, being unconscious is different from being asleep. A person can be awakened from sleep, but may or may not be able to be aroused from unconsciousness, depending on the cause.


What are the causes and risks of the condition?

There are many causes of unconsciousness, including:
  • fainting, which may occur in healthy, normal people. It often results from fatigue, pain, injury, or strong emotions such as fear. It is also common during pregnancy. Someone who faints usually wakes up within 2 minutes. Most of the time, there are no lasting problems associated with a fainting episode.
  • low blood pressure, also called hypotension. This can occur for many reasons. High blood pressure medications, serious blood loss, and dehydration are all possible causes. Orthostatic hypotension, a condition in which the blood pressure drops quickly when the person stands up, can also cause fainting.
  • medication, drug, or toxin exposure. This can include overdose with alcohol, barbiturates, or narcotics.
  • head injury. This may be mild in the case of a concussion, or more serious, as in the case of a skull fracture.
  • stroke, also called brain attack. This is brain damage that usually occurs due to a lack of oxygen. A transient ischemic attack or TIA is another cause of unconsciousness.
  • bleeding into or around the brain, which occurs with a subdural hematoma, epidural hematoma, subarachnoid hemorrhage, or severe head injury
  • infections, such as the brain infections called meningitis and encephalitis
  • low blood sugar levels, called hypoglycemia
  • diabetes that is out of control
  • severe liver disease or kidney disease
  • seizures, jerking movements or other unusual symptoms caused by abnormal electrical activity in the brain
  • low oxygen level in the blood, which can occur with severe lung or heart disease. For example, severe asthma, emphysema, irregular heartbeats called arrhythmias, severe congestive heart failure, or a blood clot in the lung, called a pulmonary embolus, can all cause low oxygen levels in the blood.
  • abnormally low body temperature, also called hypothermia
  • severe salt imbalances, such as abnormally low or high sodium levels in the blood
  • brain tumors


What can be done to prevent the condition?

Prevention of unconsciousness is related to its underlying cause. For example, avoiding drug use can prevent cases resulting from overdose. Proper treatment of diabetes can prevent many cases due to this disease. Many head injuries can be avoided by following sports safety guidelines for children, adolescents, and adults. Many cases cannot be prevented.


How is the condition diagnosed?

Sometimes the reason a person lost consciousness is obvious from the medical history and physical exam. In other cases, further tests are needed to help determine the reason for this condition, including:
  • blood chemistry tests to detect salt imbalances
  • blood sugar level to detect low blood sugar
  • liver function tests to detect serious liver disease
  • urine toxicology screens to detect drugs in a person's system or diagnose kidney disease
  • X-ray tests, such as a cranial CT scan, to detect a stroke, brain tumor, or bleeding into or around the brain
  • electroencephalogram (EEG), to check for abnormal brain waves that cause seizures
  • electrocardiogram (ECG), to detect arrhythmias or other heart disease

Long Term Effects

What are the long-term effects of the condition?

More often than not, a loss of consciousness is due to simple fainting. Usually, this has no long-term effects. Some people who faint may injure themselves as they fall to the floor. If the unconsciousness is due to a more serious cause, the long-term effects may be severe. For example, head injuries and strokes can result in permanent brain damage, disability, or death.

Other Risks

What are the risks to others?

A loss of consciousness itself is not contagious. If the loss of consciousness is due to an infection such as meningitis, the infection itself can be contagious.


What are the treatments for the condition?

Often, treatment is not needed for a simple loss of consciousness because the person usually returns to normal within a few minutes. A person who faints should be positioned on his or her back. The nearest witness able to do so should check the person's airway and breathing.
If the person remains unconscious, first aid for unconsciousness should be given:
  • Contact the emergency medical system.
  • Check the victim for signs of breathing and for airway obstruction. Also check for a pulse in the neck. If necessary, begin rescue breathing and cardiopulmonary resuscitation or CPR.
  • If a spinal cord injury is suspected, avoid moving the person except to assist breathing. If the victim is unable to breathe, gently logroll the victim into a position so rescue breathing can be started.
  • Gently restrain the victim if he or she becomes agitated.
  • Protect the victim from injury if seizures occur.
  • Keep the victim warm.
  • Stay with the victim until medical help arrives.
  • Try to get the victim to eat or drink something sweet after regaining consciousness if low blood sugar is suspected.
At the hospital, the medical team will try to maintain basic vital functions, such as breathing and blood pressure. The person may need a ventilator, or artificial breathing machine, or medications to maintain blood circulation. Oxygen, intravenous (IV) fluids, and close monitoring of the person are done routinely.
Further treatment is directed at the cause of the loss of consciousness. For example, glucose, a form of sugar, may be given to a person who has low blood sugar. If a heroin overdose is the reason for unconsciousness, naloxone (i.e., Narcan) can be given to reverse it. Someone with a subdural hematoma may need brain surgery. An individual with an infection may need antibiotics.

Side Effects

What are the side effects of the treatments?

Side effects depend on the treatments used. For example, antibiotics may cause allergic reactions or stomach upset. Surgery can be complicated by bleeding, infection, or an allergic reaction to the anesthetic.

After Treatment

What happens after treatment for the condition?

After fainting, the individual usually needs no further treatment or monitoring. Further treatment may or may not be needed for other conditions. For example, a person with serious kidney disease, liver disease, or diabetes usually needs lifelong monitoring and treatment.


How is the condition monitored?

A person who faints may receive a few tests to make sure there is not a serious cause. He or she may be observed for a brief period and then sent home. Other monitoring depends on the underlying condition. Any new or worsening symptoms should be reported to the healthcare professional.


Harrison's Principles of Internal Medicine, 1998, Fauci et al.

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