Hepatopulmonary syndrome

In medicine, hepatopulmonary syndrome is a syndrome of shortness of breath and hypoxemia (low oxygen levels in the blood of the arteries) caused by vasodilation (broadening of the blood vessels) in the lungs of patients with liver disease. Dyspnea and hypoxemia are worse in the upright position (which is called platypnea and orthodeoxia, respectively).

Diagnosis

The hepatopulmonary syndrome is suspected in any patient with known liver disease who reports dyspnea (particularly platypnea). Patients with clinically significant symptoms should undergo pulse oximetry. If the syndrome is advanced, arterial blood gasses should be measured on air.

A useful diagnostic test is contrast echocardiography. Intravenous microbubbles (> 10 micrometers in diameter) from agitated normal saline that are normally obstructed by pulmonary capillaries (normally <8 to 15 micrometers) rapidly transit the lung and appear in the left atrium of the heart within 7 heart beats. Similarly, intravenous technetium-99m–labeled albumin may transit the lungs and appear in the kidney and brain. Pulmonary angiography may reveal diffusely fine or blotchy vascular configuration. The distinction has to be made with an intracardiac right-to-left shunt.

Treatment

The main treatment is supplemental oxygen for symptoms. Other therapies, such as somatostatin to inhibit vasodilation, are of modest benefit in only some patients. Inhaled nitric oxide synthesis inhibitors may be a future treatment option. Hepatopulmonary syndrome may regress after liver transplantation or if the underlying liver disease subsides.

Prognosis is poor without treatment: the presence of hepatopulmonary syndrome worsens the prognosis, even if confounding factors such as the severity of the underlying disease (judged by the Child-Pugh score or Model for end-stage liver disease classification) are corrected.

Disease mechanism

The hepatopulmonary syndrome results from the formation of microscopic intrapulmonary arteriovenous dilatations in patients with both chronic and acute liver failure. The mechanism is unknown but is thought to be due to increased hepatic production or decreased hepatic clearance of vasodilators, possibly involving nitric oxide. The vascular dilatations cause overperfusion relative to ventilation, leading to ventilation-perfusion mismatch and hypoxemia. There is an increased alveolar-arterial partial pressure of oxygen gradient while breathing room air.

References

• Rodríguez-Roisin R, Krowka MJ (2008). Hepatopulmonary Syndrome — A Liver-Induced Lung Vascular Disorder N Engl J Med. 358:2378-2387.