What Are the Differences Between Anoxia and Hypoxia?

Anoxia happens when no oxygen supply is reaching organ tissue. In contrast, hypoxia occurs when there is a decrease in oxygen supply to organ tissues but still some being received. Getty Images

Anoxia and hypoxia are both severe, life-threatening conditions in which a person is experiencing oxygen deprivation. The terms anoxia and hypoxia are often used interchangeably, but there are differences between the two terms. Though they both describe conditions in which organs tissues, including the brain, are receiving insufficient oxygen, knowing the difference between the terms is important.

What is anoxia?

Anoxia occurs when there is no oxygen supply reaching organ tissue. Organs need oxygen to survive. Brain death occurs after approximately four minutes without an oxygen supply. For this reason, prolonged anoxia is incredibly dangerous and even short term anoxia can have detrimental health impacts. Common causes of short term anoxia are strokes and cardiac arrest. 

What is hypoxia?

Unlike anoxia which indicates a total lack of oxygen, hypoxia occurs when there is a decrease in oxygen supply to organ tissues but still some oxygen being received. With hypoxia, the damage due to lack of oxygen to the brain and other organs is more gradual than with anoxia, but brain death and impairment occur if oxygen supply is not returned quickly. 

Because both anoxia and hypoxia limit oxygen to vital organs and to the brain, there is overlap in regards to the symptoms of these two conditions. If you or someone you know is experiencing any of the following symptoms, seek medical help right away. Speed of treatment is vital for recovery from anoxia and hypoxia. 

Symptoms of anoxia 

Because anoxia deprives organs including the brain completely of oxygen, it often results in a loss of consciousness. When consciousness is regained, if the anoxia was short-term, a person may experience the following symptoms:

• Headache
• Confusion
• Difficulty with balance and motor skills
• Difficulty speaking or swallowing
• Sensory perception changes
• Changes in bladder and bowel control
• Difficulty speaking and forming sentences
• Facial drooping
• Noticeable changes in vision 
• A noticeable change in judgment
• Sudden memory loss or inattentiveness 

Symptoms of hypoxia

People who have experienced an episode of hypoxia may experience some of the anoxia symptoms listed above. Other symptoms that may indicate that you are experiencing limited oxygen supply to your brain and other organs include:

• Wheezing or trouble breathing
• Sudden alterations in skin color
• Heart rate slowing down or speeding up
• Dilation of pupils
• Confusion
• Sweating

More severe symptoms of both hypoxia and anoxia include hallucinations, seizures, prolonged periods of unconsciousness, and brain death. 

Causes of anoxia

Anoxia causes include situations in which oxygen supply is cut off completely. Examples include: 

• Drowning
• Choking
• Strangulation
• Poisoning
• Stroke
• Cardiac arrest
• Smoke inhalation 
• Drug overdose
• Trauma 

Causes of hypoxia

Hypoxia causes include situations in which some oxygen is still received, but supply is limited. Possible causes of hypoxia include:

• Carbon monoxide inhalation
• Lung inflammation
• Lung disease
• Asthma
• Strangulation
• Suffocation
• Choking, stroke
• Cardiac arrest
• Anemia
• Exposure to high altitudes 
• Ingesting of poisonous substances

Anoxia and severe hypoxia are emergent conditions. A doctor will determine whether organ tissue is receiving limited oxygen, providing a diagnosis of hypoxia, or no oxygen, providing a diagnosis of anoxia. 

If mild or moderate hypoxia is suspected, a health care provider will likely perform a physical exam to check for symptoms. A pulse oximeter may be used to check your blood oxygen level. Other tests, including an arterial blood gas test and breathing tests, may be used to assess oxygen levels. 

The primary treatment for both anoxia and hypoxia is to return adequate oxygen supply to the organs. This may involve providing respiratory assistance and establishing an airway, or in the case of mild hypoxia, treating with asthma medication or providing supplemental oxygen through a mask. People receiving treatment for severe anoxia and hypoxia may be put on medications to control their heart rate, blood pressure, and to suppress seizures.  

The severity of one's reaction to hypoxia and anoxia will depend on how long their organs were without oxygen or receiving limited oxygen. If proper support is given to a patient's respiratory and cardiovascular system, a full recovery is possible Typically, the longer someone is unconscious due to anoxia and hypoxia, the lower the chance of a full recovery. Because of the severity of both anoxia and hypoxia, psychological, neurological, and physical abnormalities may occur and persist even after oxygen supply is re-established.