Hepatopulmonary syndrome: prevalence and predictive value of various cut offs for arterial oxygenation and their clinical consequences

Abstract

Background: The hepatopulmonary syndrome (HPS) is defined as the triad of liver disease, arterial deoxygenation, and pulmonary vascular dilatation. The reported prevalence of HPS in cirrhotic patients varies between 4% and 19%, and various threshold values defining arterial deoxygenation have been used and recommended previously. However, it is not known how the prevalence of HPS differs using different cut off values for arterial deoxygenation.

Methods: We studied 127 patients for the presence of HPS using transthoracic contrast echocardiography for detection of pulmonary vasodilation, pulmonary function tests, and blood gas analysis.

Results: Ninety eight patients were included in the study, of whom 33 (34%) had a positive contrast echocardiography. Using an increased alveolar-arterial difference for the partial pressure of oxygen (AaDO(2)) as an indication of hypoxaemia, the prevalence of HPS was considerably higher (>15 mm Hg, 32%; >20 mm Hg, 31%; and >age related threshold, 28%) than using reduced partial pressure of arterial oxygen (PaO(2)) as a threshold (<80 mm Hg, 19%; <70 mm Hg, 15%; and <age related threshold, 15%). For AaDO(2) as the cut off, the positive predictive value for a diagnosis of HPS was low (34%, 37%, and 53%, respectively). In contrast, PaO(2) as a cut off had considerably higher positive predictive values (44%, 93%, and 94%, respectively). Introducing PaO(2) <65 mm Hg as the cut off, the positive predictive value increased to 100%. Dyspnoea was more often present in patients with "clinically significant" HPS (57%) compared with "subclinical HPS" (8%), and patients without HPS (6%). The Child-Pugh score correlated significantly with the severity of HPS. Two of five liver transplanted patients with "subclinical HPS" had embolic brain infarcts, possibly induced by venous emboli passing through dilated intrapulmonary vessels.

Conclusions: Defining arterial hypoxaemia in HPS by different, previously used, cut off values for arterial oxygenation leads to a wide variation in the prevalence of HPS in the same sample of cirrhotic patients.

Figure 1

Cirrhotic patients with positive or negative transthoracic contrast echocardiography according to their PaO₂ and AaDO₂ values. Previously published cut off values for a definition of hepatopulmonary syndrome were added as vertical lines in addition to those marking PaO₂ values of 60 and 65 mm Hg. PaO₂, arterial partial pressure of oxygen; AaDO₂, alveolar-arterial difference for PaO₂.

Figure 2

(A) Subgroup of patients with only mild oxygenation abnormalities (PaO₂ >70 mm Hg and AaDO₂ >age related threshold value), plotted according to their PaO₂ and AaDO₂ values, with positive or negative transthoracic contrast echocardiography. (B) Subgroup of patients with normal gas exchange (AaDO₂ <age related threshold value), plotted according to their PaO₂ and AaDO₂ values, with positive or negative transthoracic contrast echocardiography. PaO₂, arterial partial pressure of oxygen, AaDO₂, alveolar-arterial difference for PaO₂.