Question: A gifted medical student notices a cirrhotic patient on the floor in respiratory distress and spearheads a diagnostic workup. Within 24 hours the diagnosis of hepatopulmonary syndrome (HPS) is made. The student wants to know about the pathologic mechanism behind HPS. Since you want to encourage critical thinking, you ask a few questions. Which question targets the correct answer?
A. how about closing the septal defect in the heart?
B. do you think placing a TIPS will help?
C. wouldn’t it be nice if we could constrict the pulmonary vasculature?
D. maybe steroids will decrease an inflammatory component?
Answer: First of all, kudos to the student for picking up on the abnormal vital sign. Cirrhotics frequently have respiratory distress. Common causes include large ascites (restrictive pulmonary disease), hepatic hydrothorax, pneumonia, hepatopulmonary syndrome and portopulmonary hypertension.
It is hypothesized that the high amount of circulating bacterial endotoxins/antigens in cirrhotic portal hypertension triggers a cytokine-mediated vasodilatory response in the lungs. This is one of the consequences of the liver’s inability to properly filter the portal blood flow. This form of intrapulmonary vasodilation is most marked at the lung bases, which is why patients feel particularly dyspneic when upright, and relieved when recumbent.
This is not a primary defect in the heart, not directly related to portal pressures and not steroid responsive. The third question is directed at the correct pathologic mechanism: intrapulmonary shunting.