There are numerous causes of cerebral hypoxia. These include, but are not limited to:

• Drowning
• Asphyxiation caused by smoke inhalation
• Very low blood pressure
• Strangling
• Injuries during birth
• Cardiac arrest (when the heart stops pumping)
• Carbon monoxide poisoning
• High altitudes
• Choking
• Compression of the trachea
• Complications of general anasthesia
• Diseases that paralyze the respiratory muscles

Brain cells are extremely sensitive to oxygen deprivation. Some brain cells actually start dying just under five minutes after their oxygen supply is cut. As a result, brain hypoxia can kill or cause severe brain damage rapidly.

This is an emergency condition and the sooner medical attention is given and the oxygen supply restored, the lower the chances of severe brain damage and death.

In mild cases, hypoxia causes only inattentiveness, poor judgment, and motor in-coordination. Severe cases result in a state of complete unawareness and unresponsiveness where brain stem reflexes, including pupillary response to light and breathing reflex, stop.

Only blood pressure and cardiac function are maintained. If this persists, brain death is inevitable.

If the lack of oxygen to the brain is limited to a very brief period of time, coma may be reversible with varying levels of return to function, depending on the extent of injury. Sometimes seizures may occur, which may be continuous (status epilepticus).

Cerebral hypoxia can usually be deduced from the clinical history and examination. Testing is targeted at determining the cause of the hypoxia. These studies may include:

• Magnetic resonance imaging (MRI, a test which provides high-quality pictures of the brain)
• Electrocardiogram (EKG, a test of the electrical activity of the heart)
• Echocardiogram
• Blood tests (including arterial blood gases and blood sugar)
• Electroencephalogram (EEG, a test of brain waves, needed when seizures are suspected)
• Evoked Potentials (test to determine wheter certain sensations like vision and touch can reach the brain, causing an electric response)

Treatment depends on the underlying cause. Most importantly, basic life-support has to be ensured. Mechanical ventilation must be used to secure the airway; blood pressure must be supported with fluids, blood products, or medications; the heart rate needs to be controlled; and seizures treated (if they occur).

If seizures occur, some medications are used to suppress them with variable degree of success, including phenytoin, phenobarbital, valproic acid, and general anesthetics.

Sometimes cooling with blankets (hypothermia) is used because much of the brain damage in hypoxia is caused by heat, and those who suffer the condition (if it is caused by drowning in cold water, for example ) in cold temperatures have survived longer than those who were affected in higher temperatures.

However, the benefit of this treatment remains to be established. Experimental drugs called "neuroprotectants" have not shown a significant benefit so far.

Prognosis depends on the extent of the hypoxic injury which is determined by how long the brain was deprived of oxygen. Most people who make a full recovery are unconscious only briefly.

The longer the patient is unconscious, the higher the chances of death or brain death and the lower the chances of a meaningful recovery.

Complications of cerebral hypoxia include brain death or a "prolonged vegetative state" where basic life functions, such as breathing, blood pressure, sleep/wake cycle, and eye opening may be preserved, but there is no consciousness or response to the environment.

Prolonged vegetative state, however, is usually followed by death in less than one year, although rarely it may last longer. Other complications depend upon the degree of neurologic function and include: lung infections (pneumonia), improper nutrition, bed sores, and clots in the veins (deep vein thrombosis).

Prevention depends on the specific cause of hypoxia. Unfortunately, hypoxia is usually unexpected and grave. This makes this condition somewhat difficult to prevent.

Knowledge of cardio-pulmonary resucitation (CPR) maneuvers can be lifesaving, especially when they are started soon after the onset of symptoms.