Hepatopulmonary syndrome is low levels of oxygen in the blood caused by widening (dilation) of the small arteries of the lungs that occurs in people with liver disease.
Three abnormalities develop in hepatopulmonary syndrome and cause low levels of oxygen in the blood:
There is microscopic widening of arteries and veins in the lungs. Because of the widening, more blood flows through the lungs than can be adequately oxygenated by the lungs.
Blood flows through the lungs more rapidly than normal, leaving less time for the blood to receive enough oxygen.
Abnormal connections develop between arteries carrying oxygen-rich blood and veins carrying oxygen-poor blood, so that blood in the arteries that carry blood to the body has a mixture of oxygen-rich and oxygen-poor blood. That mixture has lower levels of oxygen than normal.
People have shortness of breath that is often worse when sitting up and is relieved when they lie down. The level of oxygen in the blood also decreases when the person sits up. Most people also have symptoms of chronic liver disease, such as small red spots on the skin (spider angiomas).
Doctors suspect hepatopulmonary syndrome in people with liver disease who develop shortness of breath (particularly when lying down). If hepatopulmonary syndrome is suspected, doctors measure the amount of oxygen in the blood using a sensor placed on a finger (pulse oximetry). Sometimes doctors also take a sample of blood after the person has been breathing room air and again after the person breathes oxygen and measure the levels of oxygen in the samples.
Tests that can help establish the diagnosis include a type of echocardiography in which a solution is injected intravenously (contrast echocardiography) and a nuclear lung scan.