Hepatopulmonary syndrome and porto-pulmonary hypertension had appeared in the exam at least once, as Question 28 from the second paper of 2022. In this case the candidates were instructed to compare these conditions with hepatorenal syndrome in a table presenting their definitions pathophysiology and specific treatment.
So:
Hepato-pulmonary syndrome | Porto-pulmonary hypertension | Hepatorenal syndrome |
Definitions | ||
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Pathophysiology | ||
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Specific treatment | ||
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Unless otherwise stated, the information summarised here mainly comes from the excellent paper by Benz et al (2020).
The definition for this entity, given by the ERS task force in 2005, is
"An arterial oxygenation defect induced by intrapulmonary vascular dilatations associated with hepatic disease"
The usual association is with chronic liver disease where such dilatations are more likely to form, but in all fairness even acute liver failure can produce this sort of thing, because there is nothing in the pathophysiology that might insist on a slow onset. Observe:
This is apparently seen in a large number of cirrhosis patients (up to 30%). Platypnoea (where the patients experience an improvement in respiratory distress when they are laying flat) is often found, together with orthodeoxia (where oxygenation improves with lying down and deteriorates with upright position).
The definition for this entity, given by the ERS task force in 2005, is
"Pulmonary arterial hypertension associated with portal hypertension, with or without hepatic disease"
Though the college examiners ask about the pathophysiology - there is no established scientific consensus with regards to how this thing happens. "A remodeling process of the pulmonary vasculature leads to increased pulmonary vascular resistance" is the best they can do, it seems. If one had to fill an SAQ answer with unscientific conjecture about the pathogenesis of this condition, it would consist of:
The net effect is pulmonary hypertension. Interestingly, there does not seem to be a correlation between the severity of the pulmonary hypertension and the severity of the liver disease; in other words this is not necessarily seen with just the severe end stage versions.
Pleural effusions are ubiquitous in ICU patients anyway, and so one might reasonably ask what hoops an effusion must jump through in order to be declared a "hydrothorax". The reader is reminded that pleural effusions do not form spontaneously for no specific reason, and that there is usually an explanation for them, such as heart failure, pneumonia, subdiaphragmatic collection, et cetera. A hepatic hydrothorax is therefore a pleural effusion where there is no such explanation, and where there is ascites. Specific features therefore include:
These are also usually seen on the right side (80%), more so than the left. The prevailing hypothesis for how these form involves fluid from the abdomen sloshing up into the pleural cavity along diaphragmatic defects, hitherto hidden. This also accounts for the right-sided preference of such effusions, as the diaphragm on the right is thinner and less muscular (Huang et al, 2005). As intraabdominal pressure becomes increased, the negative pressure in the pleural cavity sucks the ascites up into the chest. It does not help that these patients also concurrently experience several other "effusiogenic" influences, sich as hypoalbuminaemia and RAAS-mediated fluid accumulation.
A collection of proteinaceous fluid in the chest is an inviting culture medium for any passing organisms. It is therefore not even remotely surprising that, once a hepatic hydrothorax has formed, an empyema is not far behind. The identification of this collection would therefore rely on the finding of clinical sepsis, intrapleural organisms, and/or polymorphonuclear leukocytes on thoracocentesis (>250/μL with bugs, or >500/μL without).
Benz, Fabian, et al. "Pulmonary complications in patients with liver cirrhosis." Journal of translational internal medicine 8.3 (2020): 150-158.
Huang, Pei-Ming, et al. "The morphology of diaphragmatic defects in hepatic hydrothorax: thoracoscopic finding." The Journal of thoracic and cardiovascular surgery 130.1 (2005): 141-145.
Rodriguez-Roisin, R., et al. "Pulmonary–hepatic vascular disorders (PHD)." European Respiratory Journal 24.5 (2004): 861-880.
Krowka, Michael J. "Hepatopulmonary syndrome and portopulmonary hypertension: the pulmonary vascular enigmas of liver disease." Clinical Liver Disease 15.Suppl 1 (2020): S13.