Hypoxia (Hypoxemia)

Hypoxia is a state of insufficient oxygen supply for normal life functions, and hypoxemia is a state of low arterial oxygen supply.

Hypoxia is a condition or state in which the supply of oxygen in the arteries is insufficient for normal life functions. Hypoxemia is a condition or state in which there is a low arterial oxygen supply. Hypoxia is sometimes used to describe both states (hypoxia and hypoxemia).

Within the body, hypoxemia can lead to hypoxia (tissue hypoxia) in various tissues and organs with the most severe being cerebral hypoxia which can rapidly result in brain damage or death.

Conversely, if a person experiences environmental hypoxia (low or absent oxygen in the environment from high altitudes or drowning, for example), the person can develop hypoxemia.

• Hypoxic hypoxia (arterial hypoxia or generalized hypoxia):
  • Reduced or lack of oxygen, leading to insufficient air available to the lungs. It can occur due to high altitude, closed breathing space, etc.
  • Asthma and other disorders of the lungs, heart, or brain can also cause hypoxic ischemia (inadequate blood supply).
• Anemic hypoxia:
  • Decreased hemoglobin levels in the blood, hence there is decreased oxygen capacity of the blood. Hemoglobin is a protein in red blood cells (RBC) that binds to oxygen and supplies oxygen to the entire body. It also gives blood its characteristic red color.
  • Anemic hypoxia can be caused by heavy blood loss, decreased RBCs, or decreased hemoglobin levels due to severe iron deficiency or hemoglobin deformity.
• Ischemic/Stagnant hypoxia:
  • Inadequate blood flow to the body tissues because the velocity of blood flow decreases.
  • This could be due to heart failure, severe blood loss, or clots in a blood vessel.
• Dysoxic/Histotoxic/Tissue hypoxia:
  • The oxygen delivered to the tissues is normal, but the cells are unable to use the oxygen. For example, cyanide poisoning.
  • Cyanide binds to the oxygen-binding proteins and other parts of the cells in the tissue, preventing the interaction and consumption of oxygen in the tissues.

The causes of both environmental and tissue hypoxia often result in the intermediate state of hypoxemia; thus, the causes of any type of hypoxia are also potential causes of hypoxemia.

Some of the many causes of hypoxia include:

• Chemical or gas poisoning (for example cyanide, carbon monoxide)
• The low or absent concentration of oxygen (for example, high altitudes reached without supplemental oxygen as seen in mountain climbing, aviation, drowning, or fires)
• Lung problems, for example:
  • Chronic obstructive pulmonary disease (COPD)
  • Emphysema
  • Bronchitis
  • Pulmonary edema
  • Lung cancer
  • Pneumonia
  • Sleep apnea (nocturnal hypoxemia)
  • Pneumothorax
  • Asthma
  • COVID-19
• Any medications that reduce or stop the effort for breathing (for example, fentanyl and other narcotics, or general anesthetic medications)
• Heart problems (for example, severe bradycardia, and ventricular fibrillation)
• Anemia and/or conditions that destroy red blood cells
• Reducing or stopping arterial blood flow to any tissue for an organ (for example, arterial blockage by a clot or by injury such as a gunshot)

The symptoms of hypoxia and/or hypoxemia may be acute or chronic.

Acute symptoms can come on rapidly and usually consist of:

• Shortness of breath
• Rapid breathing
• A fast heart rate

Other associated symptoms that can occur in both acute and chronic hypoxia and hypoxemia include:

• Wheezing
• Sweating
• Coughing

The affected individual may be mildly confused initially and appear weak or may experience rapid changes in skin color ranging from blue to cherry red (depending on the causes).

Severe symptoms seen with cerebral hypoxia include:

• Confusion
• Inability to communicate
• Coma, which can lead to death

The symptoms of cerebral hypoxia in pediatric patients can be similar to the above and may include:

• Lethargy
• Irritableness
• Anxiousness
• Inattentiveness
• Sitting up and leaning forward to improve diaphragmatic breathing
• Children with epiglottitis and airway restriction may drool and mainly breathe by mouth

Blood oxygen levels can also be measured using an instrument known as a pulse oximeter.

In general, an individual patient’s hypoxemia is usually diagnosed by oxygen monitors placed on fingers or ears (pulse oximeter) and/or by determining the oxygen level in a blood gas sample (a sample of blood taken from an artery). Normal readings are about 95% to 100% oxygen saturation levels; generally, oxygen is supplied if the level is about 92% or below.

Other tests may be ordered to determine if other potential problems such as carbon monoxide poisoning are responsible for the hypoxia.

Pulmonary function tests may also be ordered along with other studies to help determine the cause of unexplained low oxygen saturation.

The treatment for hypoxia and/or hypoxemia is to give additional oxygen to the patient and into the body (blood) as quickly as possible, especially if cerebral hypoxia is suspected, or to treat the underlying cause of the hypoxia.

Many patients will respond to additional oxygen supplied by a nasal cannula. The quicker the oxygen level reaches normal, the better the prognosis is for the patient. However, timing is very important, because cerebral hypoxia can occur within a few minutes and, in many patients, may not be reversible.

Some patients may be treated in a hyperbaric chamber that increases oxygen concentrations in the blood (used in carbon monoxide poisoning), while others may require mechanical ventilation (intubation) with oxygen supplied at higher than normal atmospheric concentrations.

Others, such as mountain climbers or airline passengers, may need only additional oxygen provided by oxygen masks until they reach lower levels where oxygen concentrations are closer to the normal levels (about 21%) in the atmosphere.

Care must be used when giving oxygen, as it can be toxic to tissues if it is used excessively (hyperoxia). Hyperoxia may cause:

• Vertigo
• Behavior changes
• Other central nervous system changes such as seizures and/or tissue damage, may result in:
  • Pneumonia
  • Eye changes such as cataracts 
  • Other organ diseases/injury

Hyperoxia may occur in patients undergoing hyperbaric therapy or in long-term ICU patients.

Hypoxia causes decreased oxygenation of multiple organs such as the brain, liver, kidneys, etc., damaging them, and ultimately leading to organ failure. It can potentially lead to death. Hypoxia during pregnancy may also result in fetal death. Hypoxia in newborns is associated with a high mortality rate.

If hypoxia is identified and treated early, patients can recover without any complications.

Hypoxia and hypoxemia may be prevented in some individuals by avoiding circumstances that reduce the oxygen concentration in the environment or by providing oxygen via nasal cannula or oxygen masks before hypoxia and/or hypoxemia develop.

This can be done by recognizing individuals who tend to develop hypoxia and/or hypoxemia and providing them oxygen if they develop any early symptoms.

Moreover, some medications can provide prevention and/or relief from hypoxia/hypoxemia symptoms that are due to certain medical conditions such as asthma.