Severe arterial hypoxemia in liver cirrhosis.

The clinical symptoms in liver cirrhosis arise from portal hypertension. The classic signs and symptoms include ascites, bleeding from esophageal varices, and encephalopathy. Moreover, many patients with cirrhosis and portal hypertension develop peripheral vasodilatation and a hyperdynamic circulation with the presence of arteriovenous communications, increased blood volume, and activation of vasodilating systems such as the nitric oxide system.1,2 The hyperdynamic syndrome comprises increased heart rate, cardiac output, and plasma volume, and reduced systemic vascular resistance and arterial blood pressure. These compensatory reactions are mainly brought about by activation of potent vasoconstricting systems such as the renin-angiotensin-aldosterone system and the sympathetic nervous system. This situation has led to the appearance of new clinical entities, such as the hepatopulmonary syndrome,1 which is a pulmonary vascular disorder that complicates hepatic diseases, most frequently liver cirrhosis, and is responsible for morbidity and mortality in patients awaiting liver transplantation, primarily due to the adverse effects of hypoxemia.1,3 Knowledge about the relationship between hepatopulmonary syndrome and liver cirrhosis dates back to 1884, when Fluckiger first described it, based on observation of a woman with cyanosis, clubbing, and cirrhosis.4 However, any acute or chronic liver disease can coexist with hypoxemia due to pulmonary vascular dilatation. Therefore, portal hypertension is not required for the syndrome to manifest.2 Hepatopulmonary syndrome consists of a triad of hepatic dysfunction, hypoxemia (PaO2 70 mm Hg), and extreme vasodilatation in the form of intrapulmonary vascular dilatations. It may be further characterized by an elevated alveolar-arterial oxygen difference (P(A-a)O2), intrapulmonary shunt (diagnosed via lung-perfusion scintigraphy with technetium-99m macroaggregated albumin, or via contrast-enhanced echocardiography), and the absence of arterial carbon dioxide retention.5 A lung-perfusion scintigram can indicate the shunt fraction from the right-kidney scintigraphic count, corrected for attenuation. The fraction is expressed as a percentage of the injected dose, with the right-to-left shunt expressed as 10 times that value, assuming the right kidney received 10% of the cardiac output (kidney-dose method). The kidney-lung method calculates the right-kidney count as a proportion of the lung counts.6 Another modality to investigate thoracic shunt is contrast-enhanced echocardiography. Saline is agitated to produce microbubbles ( 15 m in diameter) and the agitated saline is injected intravenously. Under normal circumstances the microbubbles are trapped in the pulmonary microvasculature and then absorbed. In patients with intracardiac or intrapulmonary shunt the microbubbles appear in the left-side cardiac chamber. Differentiation between intracardiac and intrapulmonary shunt is based on the timing of when the bubbles reach the left heart chamber. In intracardiac right-to-left shunt the bubbles appear in the left heart chamber within 3 heartbeats after they appear in the right heart chamber. In intrapulmonary shunt the bubbles appear in 4–6 heartbeats.7,8 The severity of hepatopulmonary syndrome can be classified by the degree of P(A-a)O2. Rodrı́guez-Roisin et al described the degrees of severity from mild (P(A-a)O2 15 mm Hg, PaO2 80 mm Hg) to very severe (P(A-a)O2 15 mm Hg, PaO2 50 mm Hg). 9