Hepatopulmonary syndrome is a rare complication of liver disease. Failure or poor function of the liver begins a complex chain of events that leads to the lungs being incapable of the effective transfer of oxygen. This is hepatopulmonary syndrome, and it can cause various breathing and other concerning symptoms. Though doctors are now able to recognize hepatopulmonary syndrome easily, many specifics about the disease and its causes remain unknown.
Doctors generally identify three key features of hepatopulmonary syndrome. Primarily, the individual must have some form of liver disease. Usually, this includes liver dysfunction or extraordinarily high blood pressure in the vein that transfers blood from the intestine to the liver. The person must also be experiencing a widening of the blood vessels that deliver to the lungs. Finally, the individual must experience abnormal oxygenation. Though there is some variability, almost all cases of hepatopulmonary syndrome meet these three criteria.
An overwhelming majority of patients with hepatopulmonary syndrome report liver problems first and eventually develop breathing issues. The most common symptom is shortness of breath (dyspnea), which can happen both when the person is at rest and exerting themselves. This occurs in over 95% of patients and usually develops years after the liver issues. The most specific complaint is platypnea, breathlessness in a sitting or standing position that improves while lying down. Some people develop a blue coloration to their skin and mucous membranes that physicians call cyanosis. Doctors can discover hypoxemia, low oxygen levels within the blood of the arteries, in patients with these symptoms.
The very first report of hypoxemia in patients with liver disease occurred in 1884. Flückiger M. Vorkommen was a researcher who provided many contributions to the world of medicine. One of his largest findings was the presence of cyanosis, digital clubbing, and hypoxemia in patients with chronic liver disease. A century later, in 1977, two other researchers examined a patient with these symptoms. They ultimately described the condition as “hepatopulmonary syndrome.”
In general, physicians and researchers do not know the cause of hepatopulmonary syndrome. It is also unknown why some individuals with liver disease develop hepatopulmonary syndrome while others do not. At the most basic level, liver disease causes the blood vessels in the lungs to dilate. If the dilation is severe, the lungs can fail to properly transfer oxygen. Current research efforts generally focus on learning why the blood vessels that enter the lungs dilate in response to liver disease. The modern theory is that liver disease prevents the release of certain factors and this, in turn, prevents blood vessel cell growth.
Currently, hepatopulmonary syndrome is so rare that most research on the condition stems from animal studies. Some use bile duct ligation in rats to force liver cirrhosis. This causes symptoms similar to hepatopulmonary syndrome. Thanks to these studies, researchers discovered molecules that offer new perspectives for understanding hepatopulmonary syndrome’s development. These new molecules may one day provide future targets for the treatment of hepatopulmonary syndrome.
Most cases of hepatopulmonary syndrome fall into one of four degrees of severity -- mild, moderate, severe, and very severe -- depending on the level of hypoxemia. Screenings of patients with hepatopulmonary syndrome show that most cases are mild to moderate. Earlier studies showed that there were more people with severe and very severe degrees of the condition, but this was due to poor screening criteria. Regardless of the degree of severity, people with hepatopulmonary syndrome have a significantly lower quality of life due to breathing issues and lack of oxygen while sleeping.
Some people with liver disease develop a complication similar to hepatopulmonary syndrome. Portopulmonary hypertension is another abnormality of the pulmonary vasculature. This means that, like hepatopulmonary syndrome, the condition affects the blood vessels entering the lungs. However, hepatopulmonary syndrome causes vasodilation, which is an expanding of these blood vessels. Portopulmonary hypertension causes vasoconstriction, a narrowing of these blood vessels.
Dyspnea is a common symptom of liver disease. Because of this, doctors often fail to diagnose hepatopulmonary syndrome until it worsens. Pulmonary function tests usually discover the signs of the syndrome, but these findings often match the symptoms of normal liver cirrhosis. Tests such as echocardiograms can discover if the blood vessels around the lungs are dilating. A macroaggregated albumin lung perfusion scan is the most effective means of discovering the full extent of hepatopulmonary syndrome’s effects. This scan uses a small number of radioactive particles and a special camera to detect to where in the body the particles travel.
Though many clinical studies are searching for effective hepatopulmonary syndrome treatments, there is currently only one: a full liver transplant. Along with the transplant doctors continue long-term oxygen therapy. They may also perform post-operative pulmonary rehabilitation to help increase the patient's lung capacity and strength and reduce the symptoms of the syndrome.
For the majority of patients, a liver transplant significantly improves oxygenation within a year of the procedure. Liver transplant patients also have significantly higher five-year survival rates than individuals with hepatopulmonary syndrome who do not receive a transplant. Because hypoxemia is progressive, most doctors recommend a transplant as quickly as possible. Without one, a person with hepatopulmonary syndrome will have a significantly reduced quality of life and the disease will likely result in death within several years.
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