The cause of hypoxemia may be:

• Less oxygen in the air you breathe, such as at elevations high above sea level.
• Breathing that's too slow or shallow to meet the lungs' need for oxygen.
• Not enough blood flow to the lungs or not enough oxygen to the lungs.
• Trouble with oxygen getting into the bloodstream and the waste gas carbon dioxide getting out.
• An issue with how blood flows in the heart.
• Changes in the protein called hemoglobin, which carries oxygen in red blood cells.

Causes of hypoxemia that are linked to issues with blood or blood flow include:

1. Anemia — a condition in which the body doesn't get oxygen due to a lack of healthy red blood cells
2. Congenital heart defects in children — heart conditions that children were born with
3. Congenital heart disease in adults — heart issues that adults were born with

Breathing conditions that can lead to hypoxemia include:

1. ARDS (acute respiratory distress syndrome) — a lack of air due to a buildup of fluid in the lungs
2. Carbon monoxide poisoning
3. COPD — (chronic obstructive pulmonary disease) — the blanket term for a group of diseases, including emphysema, that block airflow from the lungs
4. Guillain-Barre syndrome — a condition in which the body's immune system attacks the nerves
5. Interstitial lung disease — the term for a large group of conditions that scar the lungs
6. Myasthenia gravis — a condition that weakens the muscles you control
7. Pneumonia — an infection in one or both lungs
8. Pneumothorax — a collapsed lung
9. Pulmonary edema — too much fluid in the lungs
10. Pulmonary embolism — a blood clot in an artery in the lung
11. Pulmonary fibrosis — a condition that happens when lung tissue becomes damaged and scarred
12. Sepsis — a life-threatening condition in which the immune system reacts too strongly to an infection
13. Sleep apnea — a condition in which breathing stops and starts many times during sleep

Some medicines that can make breathing slow and shallow can lead to hypoxemia. These include some opioid pain relievers. Medicines that prevent pain during surgery and other procedures, called anesthetics, also can cause hypoxemia.