Hepatopulmonary Syndrome: What the Pulmonologist should Know?

efficient transfer of oxygen.In HPS, massively dilated capillaries (15-500 m) form functional AV shunts, permitting blood to bypass gas exchange in the alveoli, which is referred to as diffusion limitation.Simultaneously, blood moves rapidly through these abnormally dilated vessels, which does not allow enough time for complete oxygenation, leading to a profound V/Q mismatch.Cirrhosis is characterized by impaired clearance of gut-derived vasodilators, such as NO and carbon monoxide, in the liver, leading to diffuse vasodilation in the pulmonary circulation, particularly in the lower lung fields.The extensive vasodilation in the lower parts of the lungs explains the classic symptoms of platypnea and orthodeoxia.With the patient standing upright, more blood goes to the lower lungs, which are the most severely involved, and gaseous exchange of oxygen becomes ineffective.