Hypoxemia in a patient with end-stage liver disease

A number of pulmonary conditions producing hypoxemia may affect patients with chronic liver disease. Among these conditions, hepatopulmonary syndrome (HPS) is common, with the estimated prevalence of HPS among patients with end-stage liver disease ranging from 4% to 29%. HPS is considered present when the triad of liver dysfunction and/or portal hypertension, intrapulmonary vascular dilatation, and abnormal arterial oxygenation are noted in the absence of intrinsic cardiopulmonary disease. The pathogenesis of HPS is still unclear but is likely related to the effects of nitrous oxide and other vasoactive substances on the pulmonary vascular endothelium. HPS primarily affects the precapillary arterioles and capillaries in the lung bases, producing dilation of these vessels. These dilated vessels may produce hypoxemia through a combination of several mechanisms, including true anatomic shunts, ventilation-perfusion mismatch, and diffusion-perfusion defects. Chest radiographic imaging findings of HPS may be subtle and primarily consist of basilar reticular and nodular opacities. Thoracic CT often shows dilated peripheral pulmonary arteries with normal central pulmonary arteries. Pulmonary angiography may show dilated peripheral pulmonary arteries and early venous filling. ^99mTechnetium-labeled macroaggregated albumin scans may show systemic embolization of radioactive tracer. Treatment of HPS consists of supplemental oxygen and, in severe cases, orthotopic liver transplantation.