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Cerebral hypoxia is the medical term for lack of oxygen to the brain. The brain requires 3.3 ml of oxygen per 100 g of tissue every minute. When that amount isn't being achieved, the body struggles to adjust, for example in high altitudes. But when the oxygen deprivation is too sudden or too severe, the body cannot adjust. Brain function begins to shut down.

Causes

Sometimes diseases like asthma or anemia can limit the amount of oxygen that reaches the brain, causing mild to moderate cerebral hypoxia. External factors like deep-sea diving, flying in an unpressurized plane, choking, strangulation or drowning can all cause moderate to severe cerebral hypoxia. A reaction to anesthesia can cause cerebral hypoxia, coma or even death.

Symptoms

Unlike with the more traumatic, severe forms of cerebral hypoxia, the milder forms may be difficult to spot. Symptoms include a loss of motor skills, a lightheaded feeling, fainting, increased heart rate, and/or seizures.

Increased heart rate may exhaust the heart as it struggles to pump oxygen through the body to the brain. The heart may stop beating, requiring CPR, defibrillation or an injection of drugs like epinephrine (used by people with severe food or bee allergies) to get the heart pumping again.

Very severe cases of prolonged hypoxia can lead to coma and even brain death. During and after severe oxygen deprivation, cells in the brain may die due to an increase in acidity in the brain tissue. This increase in acidity is called “acidosis.”

Even after the return of oxygen to the brain, a problem called “reperfusion injury” may damage the brain. While deprived of oxygen, brain cells build up oxidizing free radicals that will then be let loose into the brain and nerves after the oxygen supply returns. Reperfusion injury is generally treated with therapeutic hypothermia, where a patient's body temperature is lowered to prevent cells and membranes from being attacked by the free radicals.

Treating Cerebral Hypoxia

In most cases, just eliminating the cause can reverse the symptoms. For example, if a person is choking, usually clearing their airway will cause breathing to return to normal and symptoms to disappear.

In more severe cases, an oxygen mask and/or mechanical ventilation (a respirator) will be used to increase blood oxygen in an effort to get that oxygen to the brain.

Neo-Natal Cerebral Hypoxia

A complicated birth may result in the baby losing oxygen to the brain. Perhaps an umbilical cord gets wrapped around the baby's throat, or the baby becomes trapped in the birth canal. This is called neonatal encephalopathy and can lead to cerebral palsy. Therapeutic hypothermia is commonly used on newborns to help limit or reverse the damage done by a difficult birth. If done within six hours of cerebral hypoxia, therapeutic hypothermia can significantly improved the neurological outcome for newborns.

Outcome

Prognosis of hypoxia patients varies depending on the severity of the damage, the length of time the brain was deprived of oxygen and the damage-control measures used during the episode. In mild or moderate cases, there is generally no long-term effect. The symptoms disappear after the episode of hypoxia. Once oxygen is restored to the brain, the person recovers quickly with no long-term effects.

If severe hypoxia was localized, the damage will usually be localized as well. For example, if the left brain was deprived of oxygen for a prolonged period, speech patterns and language may be affected. Damage to the right side may lead to emotional issues.

Paralysis is a potential outcome of severe, prolonged hypoxia – such as a coma. The longer a person is in a non-medically induced coma (such as the kind used for severe burn victims) the more severe the damage to the brain will be. The patient may remain in a vegetative state for the rest of their lives. They may awake to some functionality, but it may be limited. Coma patients often have to re-learn skills such as walking, talking and personal hygiene. Short and long-term memory may be severely affected; patients may not even remember the names of those closest to them, such as spouses or children.