Hepatopulmonary syndrome: What we know and what we would like to know

Abstract

Hepatopulmonary syndrome (HPS) is characterized by abnormalities in blood oxygenation caused by the presence of intrapulmonary vascular dilations (IPVD) in the context of liver disease, generally at a cirrhotic stage. Knowledge about the subject is still only partial. The majority of the information about the etiopathogenesis of HPS has been obtained through experiments on animals. Reported prevalence in patients who are candidates for a liver transplantation (LT) varies between 4% and 32%, with a predominance of mild or moderate cases. Although it is generally asymptomatic it does have an impact on their quality of life and survival. The diagnosis requires taking an arterial blood gas sample of a seated patient with alveolar-arterial oxygen gradient (AaO2) ≥ 15 mm Hg, or ≥ 20 mm Hg in those over 64 years of age. The IPVD are identified through a transthoracic contrast echocardiography or a macroaggregated albumin lung perfusion scan ((99m)Tc-MAA). There is currently no effective medical treatment. LT has been shown to reverse the syndrome and improve survival rates, even in severe cases. Therefore the policy of prioritizing LT would appear to increase survival rates. This paper takes a critical and clinical look at the current understanding of HPS, as well as the controversies surrounding it and possible future research.

Keywords: Contrast echocardiography; Hepatopulmonary syndrome; Liver cirrhosis; Liver transplantation; Macroaggregated albumin lung perfusion scan.

Figure 1

Hypothesis for the natural history of hepatopulmonary syndrome. HPS: Hepatopulmonary syndrome; AaO₂: Alveolar-arterial oxygen gradient; DLCOco: Corrected diffusing capacity for carbon monoxide; ^99mTc-MAA: Macroaggregated albumin lung perfusion scan.

Figure 2

Hepatopulmonary syndrome screening model and diagnosis in liver transplantation candidates. AaO₂: Alveolar-arterial oxygen gradient; HPS: Hepatopulmonary syndrome; LT: Liver transplantation; pO₂: Partial oxygen pressure; Sat O₂: Arterial oxygen saturation; ^99mTc-MAA: Macroaggregated albumin lung perfusion scan.