Hepatopulmonary (hep-uh-toe-POOL-moe-nar-e) syndrome is caused by blood vessels in the lungs expanding, also called dilating, and increasing in number. This condition affects the lungs of people who have advanced liver disease.

These changes in the lungs make it hard for red blood cells to take in oxygen. Then the lungs can't send enough oxygen to the body. This leads to low oxygen levels in the blood, also called hypoxemia.

How liver disease is linked to the lung condition isn't yet known. A liver transplant is the only cure for hepatopulmonary syndrome.

Often, there are no symptoms of hepatopulmonary syndrome. If there are symptoms, they can include:

• Shortness of breath that's worse when sitting or standing and gets better when lying down.
• Clubbing of the fingers, in which the fingertips spread out and become rounder than usual.
• Broken blood vessels under the skin, called spider angioma.
• Bluish tinge of the lips and skin in white people. In Black and brown people, the lips or tongue might look light gray. This change in color is called cyanosis.

Hepatopulmonary syndrome is caused when blood vessels in and around the lungs widen, also called dilate. This affects the amount of oxygen that moves from the lungs into the bloodstream.

What causes this is not clear. And it's not known why some people with liver disease develop hepatopulmonary syndrome while others do not.

These tests can help find if you have hepatopulmonary syndrome:

• Arterial blood gas. For this test, blood is taken from an artery to measure levels of oxygen and carbon dioxide and the pH balance.
• Chest imaging. X-rays, CT scanning or echocardiogram imaging with a salt solution given through a vein, called a saline contrast study, can help rule out other heart or lung conditions.
• Pulse oximetry. In pulse oximetry, a sensor attached to the finger or ear uses light to see how much oxygen is in the blood.

Being given oxygen, called supplemental oxygen therapy, is the main treatment for shortness of breath caused by low oxygen levels in the blood. A liver transplant is the only cure for hepatopulmonary syndrome.