What is hepatopulmonary syndrome (HPS)?

Hepatopulmonary syndrome (HPS)

Hepatopulmonary syndrome (HPS) is characterised by an oxygenation defect induced by pulmonary vascular dilatation in patients with liver cirrhosis or portal hypertension with no evidence of primary pulmonary disease. 

The oxygenation defect which results in resistant hypoxaemia (PaO2 < 9.3 kPa (70 mmHg)), consists of a wide alveolar-arterial gradient (AAG) (>15mmHg). The vascular dilatation is thought to be induced by increased pulmonary levels of nitric oxide (NO). Beside of the vascular dilatation, intrapulmonary shunting through direct arteriovenous communications is also seen which leads to hypoxia. The HPS is seen in 15-30% of patients with cirrhosis and is a poor prognostic indicator. 

Clinical features of HPS:

• Most patients with hepatopulmonary syndrome are asymptomatic or have dyspnoea with an insidious onset. 
• Dyspnoea whilst standing (platypnoea) and hypoxemia exacerbated by being upright (orthodeoxia) are characteristic [These are thought to be due to the predominance of vascular dilatation in the lung bases. Blood flow to these areas is increased in the upright position.]
• Desaturation during sleep is also often seen
• Cyanosis
• Features of cirrhosis (e.g. spider naevi, clubbing etc.) are found. 

Investigations of HPS:

• Contrast-enhanced transthoracic echocardiography (agitated saline or bubble study) is the best test to demonstrate intrapulmonary vascular dilatation [It can also exclude intracardiac shunting which may result in similar signs and symptoms to hepatopulmonary syndrome.]
• Chest radiographs can be normal or show non-specific interstitial changes. 
• ABGs should be taken in the sitting position to grade the severity of the condition based on the degree of hypoxemia. 
• In Pulmonary Function Tests: Decreased DLCO.

Treatment of HPS:

• Liver transplantation is the only proven beneficial available treatment, with 85% of patients showing resolution or significant improvement in gas exchange postoperatively. But severe hypoxemia (PaO2< 6.7 kPa (50 mmHg)), is associated with an increased operative risk.

Additional:

How to perform or interpret agitated saline study?

This is performed by injecting agitated saline IV during transthoracic echocardiography. 

• In a normal subject, microbubbles are visualised in the right ventricle within seconds, which are then absorbed in the alveoli. 
• Immediate visualisation in the left ventricle (within 3 cardiac cycles) indicates intracardiac shunting. 
• Delayed visualisation in the left ventricle (3-6 cardiac cycles) is diagnostic of intrapulmonary shunting.

Watch this YouTube video on Agitated saline study 

Source:

• Step Up to MRCP Review Notes for P1 & P2 By Dr Khaled El Magraby 1st ed 2015; page 274
• Davidson's Principles and Practice of Medicine; 23rd Edition; page 898
• Kumar and Clark's clinical medicine, 9th Edition; page 475
• Zakim and Boyer's Hepatology- A Textbook of Liver Disease, 6th Edition; page 394