Hepatopulmonary Syndrome: Pathophysiology

Hepatopulmonary syndrome is a condition in patients with liver disease that is characterized by arterial hypoxemia caused by pulmonary vasodilatation. Patients with Hepatopulmonary syndrome have dyspnea, which can be severe, in addition to other signs of hypoxemia such as cyanosis and digital clubbing. Another sign suggestive of this syndrome is orthodeoxia (a decrease in arterial PaO₂ with a change in position from supine to upright), which may cause the patient to feel the symptom of platypnea (worsening shortness of breath when changing position from supine to sitting or standing).

The pulmonary vasodilatation that occurs in hepatopulmonary syndrome is thought to be secondary to an increase in nitric oxide within the pulmonary vascular endothelium via an increase in nitric oxide synthase. The pulmonary capillary vasodilatation leads to increased blood flow to some alveoli without an increase in alveolar ventilation to those areas leading to a ventilation perfusion mismatch. In addition to V/Q mismatch, intrapulmonary shunts also develop through pleural and pulmonary arterio-venous communications which further exacerbate the arterial hypoxemia seen in this condition.

Hepatopulmonary syndrome is often confused with portopulmonary hypertension, which should only lead to mild hypoxemia. Portopulmonary hypertension is an obstruction of blood flow through the pulmonary arterial bed caused by vasoconstriction which leads to an increased PVR with eventual right heart failure.