Brain cells are extremely sensitive to a lack of oxygen. Some brain cells start dying less than 5 minutes after their oxygen supply disappears. As a result, brain hypoxia can rapidly cause severe brain damage or death.
Symptoms of mild cerebral hypoxia include:
Change in attention (inattentiveness)
Symptoms of severe cerebral hypoxia include:
Complete unawareness and unresponsiveness (coma)
No response of the pupils of the eye to light
Signs and tests
Cerebral hypoxia can usually be diagnosed based on the person's medical history and a physical exam. Tests are done to determine the cause of the hypoxia, and may include:
If only blood pressure and heart function remain, the brain may be completely dead.
Cerebral hypoxia is an emergency condition that need to be treated right away. The sooner the oxygen supply is restored to the brain, the lower the risk of severe brain damage and death.
Treatment depends on the cause of the hypoxia. Basic life support is most important. Treatment involves:
Breathing assistance (mechanical ventilation)
Controlling the heart rate and rhythm
Fluids, blood products, or medications to raise blood pressure if it is low
Medications including phenytoin, phenobarbital, valproic acid, or general anesthetics to calm seizures
Sometimes a person with cerebral hypoxia is cooled to slow down the activity of the brain cells and decrease their need for oxygen. However, the benefit of this treatment has not been firmly established.
The outlook depends on the extent of the brain injury. This is determined by how long the brain lacked oxygen, and whether nutrition to the brain was also affected.
If the brain lacked oxygen for only a very brief period of time, a coma may be reversible and the person may have a full or partial return of function. Some patients recover many functions, but have abnormal movements such as twitching or jerking, called myoclonus. Seizures may sometimes occur, and may be continuous (status epilepticus).
Most people who make a full recovery were only briefly unconscious. The longer a person is unconscious, the higher the risk for death or brain death, and the lower the chances of recovery.
Complications of cerebral hypoxia include a prolonged vegetative state. This means the person may have basic life functions such as breathing, blood pressure, sleep-wake cycle, and eye opening, but the person is not alert and does not respond to his or her surroundings. Such patients usually die within a year, although some may survive longer.
Length of survival depends partly on how much care is taken to prevent other problems. Major complications may include:
Daniel B. Hoch, PhD, MD, Assistant Professor of Neurology, Harvard Medical School, Department of Neurology, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.