Hypoxic encephalopathy

Alternative names

Cerebral hypoxia

Definition

The term cerebral hypoxia technically refers to a lack of oxygen supply to the cerebral hemispheres (the outer portion of the brain), but it is more typically used to refer to a lack of oxygen supply to the entire brain.

Causes, incidence, and risk factors

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

• Drowning
  
• Drug overdose
  
• Asphyxiation caused by smoke inhalation
  
• Very low blood pressure
  
• Strangulation
  
• 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 less than 5 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.

Symptoms

In mild cases, hypoxia causes only inattentiveness, poor judgment, and motor in-coordination. Severe cases result in a state of complete unawareness and unresponsiveness - 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).

Signs and tests

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), which provides high-quality pictures of the brain