OVERVIEW
Hepatopulmonary syndrome (HPS) is a condition of hypoxemia and a series of pathophysiological changes and clinical manifestations resulting from abnormal dilatation of intrapulmonary vasculature, impaired gas exchange, and abnormal arterial blood oxygenation on the basis of chronic liver disease and/or portal hypertension, and is clinically characterized by the triad of the following: exclusion of primary cardiorespiratory disorders – underlying liver disease, Intrapulmonary vasodilation and arterial blood oxygenation dysfunction. Abnormal arterial blood oxygenation due to impaired pulmonary gas exchange – rising alveolar gas-arterial blood oxygen partial pressure difference and hypoxemia – is an important physiologic basis for hepatopulmonary syndrome. Hepatopulmonary syndrome is a serious pulmonary complication of end-stage liver disease.
Etiology.
Etiology of liver disease causing hypoxemia: Various acute and chronic liver diseases can be associated with pulmonary vascular abnormalities and arterial hypoxemia, most notably cirrhosis due to chronic liver disease, especially cryptogenic cirrhosis, alcoholic cirrhosis, hepatitis cirrhosis and primary biliary cirrhosis. Portal hypertension may be a major pathogenetic factor in hepatopulmonary syndrome and has not been found to correlate with the severity of cirrhosis. The development of hepatopulmonary syndrome is the result of multiple factors and cannot be explained solely by portal hypertension or hepatic insufficiency.
Symptoms
The disease consists of a triad of intrapulmonary vasodilatation and insufficient arterial oxygenation caused by primary liver disease. The clinic is characterized by primary liver disease and pulmonary lesions, and the characteristic manifestations of the hepatopulmonary syndrome are upright positional dyspnea, hypoxemia, and cyanosis.
1. Clinical manifestations of primary liver disease
There are great differences due to the degree of liver cell function damage and complications, the most common ones are liver palms, spider nevus, jaundice, hepatosplenomegaly, abdominal effusion, gastrointestinal hemorrhage, liver function abnormality and so on. Liver-lung syndrome has nothing to do with the cause and degree of liver disease, and some patients with stable liver disease may also show progressive decompensation of lung function. Pulmonary vasodilatation (pulmonary spider nevus) is often found in liver disease patients with subcutaneous spider nevus, which is prone to hypoxemia, and subcutaneous spider nevus is considered to be a sign of extrahepatic invasion.
2. Clinical manifestations of pulmonary dysfunction
Patients have no primary cardiopulmonary disease, and most of them gradually develop respiratory manifestations on the basis of liver disease, such as cyanosis, dyspnea, pestle-like fingers (toes), upright hypoxia, and supine respiration. Progressive dyspnea is the most common pulmonary symptom of hepatopulmonary syndrome, cyanosis is the only reliable clinical sign, and supine respiration and upright hypoxia are the most characteristic manifestations of this disease. Pulmonary examination is usually without obvious positive signs.
Examination
1. Lung function measurement
Lung capacity, maximal ventilation, functional residual air volume, total lung volume, respiratory reserve volume, R/T, expiratory volume in one second, and pulmonary carbon monoxide diffusion volume can be measured. In patients with hepatopulmonary syndrome without obvious pleural or abdominal effusion, although lung volume and expiratory volume may be basically normal, there is still a more obvious change in diffusion volume, which is still obviously abnormal even after correction for hemoglobin.
Arterial blood gas analysis: alveolar partial pressure of oxygen is decreased in hepatopulmonary syndrome, less than 70 mmHg; SaO2 is decreased, less than 90%. In upright and supine position, PaO2 decreases and is greater than 10mmHg; A-aPO2 gradient rises 15-20mmHg. PaO2 measurement is also valuable when breathing room air and 100% oxygen. a-aPO2 is more sensitive than PaO2 and can be used as the main diagnostic basis for hepatopulmonary syndrome.
2. Echocardiography
Transthoracic echocardiography and transesophageal echocardiography can identify the site of the lesion. Transesophageal echocardiography is more sensitive than transthoracic echocardiography and correlates with gas exchange disorders.
3. Pulmonary angiography
Type I – diffuse anterior capillary dilatation: diffusely distributed spider-like images, diffusely distributed spongy or stain-like images, and PaO2 can be elevated by inhaling 100% oxygen. Type II – intermittent localized arteriovenous malformations or traffic branches: isolated earthworm-like or doughnut-shaped images, inhalation of 100% oxygen has no effect on PaO2.
4.CT examination
CT in patients with hepatopulmonary syndrome may show distal pulmonary vasodilatation with a large number of abnormal terminal branches, which may suggest the presence of hepatopulmonary syndrome, but it is not specific.
5. Chest X-ray
The manifestation of hepatopulmonary syndrome is not specific, but the chest X-ray in standing position can show interstitial infiltration at the base of both lungs, which is the shadow of vasodilatation, and disappears when lying down, and it needs to be distinguished from interstitial pulmonary fibrosis.
Diagnosis
Hepatopulmonary syndrome can be diagnosed if the following conditions are met:
1. acute or chronic liver disease, liver dysfunction is not necessarily obvious.
2. absence of primary cardiopulmonary disease with normal or interstitial nodular shadows on X-ray chest radiograph.
3. Abnormal pulmonary gas exchange, with or without hypoxemia, and an A-aPO2 gradient greater than 15 mmHg.
4. presence of pulmonary vasodilatation and/or short-circuiting of intrapulmonary vessels on contrast-enhanced echocardiography and/or lung perfusion scan, pulmonary angiography.
5. hypoxia, shortness of breath, cyanosis, and pulmonary osteoarthropathy in the upright position.
Treatment
1. General treatment
This includes treating the primary disease, improving liver function or slowing the progression of cirrhosis, decreasing portal pressure, and potentially reducing right-to-left shunting in the lungs.
2. Oxygen intake and hyperbaric chamber
Suitable for patients with mild, early hepatopulmonary syndrome, can increase the concentration and pressure of oxygen in the alveoli and help oxygen diffusion.
3. Embolization
For embolization of isolated pulmonary arteriovenous traffic branches, i.e., patients with hepatopulmonary syndrome with pulmonary angiography type II.
4. Transjugular intrahepatic portosystemic shunt (TIPS)
It can improve the oxygenation of patients with hepatopulmonary syndrome, and both PaO2 and alveolar arterial oxygen partial pressure difference can be significantly improved, and the patient’s symptom of dyspnea is better.
5. In situ liver transplantation
It is the fundamental treatment for hepatopulmonary syndrome and can reverse pulmonary vasodilatation. Progressive hypoxemia combined with hepatopulmonary syndrome can be an indication for liver transplantation.
6. Pharmacologic treatment of hepatopulmonary syndrome.
Progress is slow and efficacy is unsatisfactory. Octreotide, a potent vasodilator neuropeptide inhibitor, is thought to reduce intrapulmonary arteriovenous shunting in patients with hepatopulmonary syndrome by blocking neuropeptides, vasoactive peptides, and inhibiting glucagon. Allylpiperazine improves the ventilation/blood flow ratio in chronic obstructive pulmonary disease by causing vasoconstriction in hypoxic lungs, which improves the pulmonary ventilation/blood flow ratio. Clinical use of methylene blue increases pulmonary vascular resistance and corporal circulation vascular resistance and improves hypoxemia and hyperdynamic circulation in patients with hepatopulmonary syndrome. None of the pharmacological treatments are currently recognized.
Prognosis.
Patients with cirrhosis presenting with hepatopulmonary syndrome have a poor prognosis.