Chapter 2　Defnition and Pathogenesis of Hepatopulmonary Syndrome

Hepatopulmonary syndrome (HPS), a liver disease-induced lung vascular disorder,is characterized by intrapulmonary vascular dilation (IPVD) that causes hypoxemia in the setting of advanced liver diseases. It presents clinically with ventilation-perfusion mismatch, which is marked by increased room air alveolar-arterial oxygen gradient (AaPO ₂) (＞15 mmHg, or＞20 mmHg when age ≥65 years), with or without hypoxemia. It occurs as a result of IPVD and arteriovenous shunting in association with hepatic dysfunction or portal hypertension ¹. Because the symptom of HPS is generally unconspicuous, the patient candidates for live transplantation must be checked for the possibility of HPS. Some clinical symptoms, such as spider naevi, digital clubbing and cyanosis, have been regarded as the indicator of the HPS.Unfortunately, all these signs are not specific for the patients. Progressive dyspnea with standard of PaO ₂＜70 mmHg is useful to identify clinically significant HPS, while it is not a special symptom for HPS. In contrast, digital clubbing has been the most positive predictor ². Although the diagnosis of HPS has been improved in the past decades, some other causes of cardiopulmonary dysfunction still need to be identifed. Given that AaPO ₂ value is increased with age and it varies signifcantly even in healthy adults, the application of confdence interval values above 95% for the age-corrected AaPO ₂ will be very helpful to avoid the excessive diagnosis of HPS. The defnition of HPS, based on some standard diagnosis factors, will be more appropriated in the future.