Hepatopulmonary syndrome
Encyclopedia
In medicine
, hepatopulmonary syndrome is a syndrome
of shortness of breath and hypoxemia
(low oxygen levels in the blood of the arteries) caused by vasodilation
(broadening of the blood vessels) in the lungs of patients with liver disease
. Dyspnea and hypoxemia are worse in the upright position (which is called platypnea
and orthodeoxia, respectively).
. If the syndrome is advanced, arterial blood gas
ses should be measured on air.
A useful diagnostic test is contrast echocardiography
. Intravenous microbubbles (> 10 micrometers in diameter) from agitated normal saline that are normally obstructed by pulmonary capillaries (normally <8 to 15 micrometers) rapidly transit the lung and appear in the left atrium
of the heart within 7 heart beats. Similarly, intravenous technetium
-99m–labeled albumin
may transit the lungs and appear in the kidney and brain. Pulmonary angiography may reveal diffusely fine or blotchy vascular configuration. The distinction has to be made with an intracardiac right-to-left shunt
.
. The mechanism is unknown but is thought to be due to increased hepatic production or decreased hepatic clearance of vasodilators, possibly involving nitric oxide.
The vascular dilatations cause overperfusion relative to ventilation, leading to ventilation-perfusion mismatch and hypoxemia. There is an increased alveolar
-arterial partial pressure
of oxygen gradient
while breathing room air. Additionally, late in cirrhosis, it is common to develop high output failure, which would lead to less time in capillaries per red blood cell, exacerbating the hypoxemia.
or somatostatin
to inhibit vasodilation remain anecdotal.
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
, hepatopulmonary syndrome is a syndrome
Syndrome
In medicine and psychology, a syndrome is the association of several clinically recognizable features, signs , symptoms , phenomena or characteristics that often occur together, so that the presence of one or more features alerts the physician to the possible presence of the others...
of shortness of breath and hypoxemia
Hypoxemia
Hypoxemia is generally defined as decreased partial pressure of oxygen in blood, sometimes specifically as less than or causing hemoglobin oxygen saturation of less than 90%.-Distinction from anemia and hypoxia:...
(low oxygen levels in the blood of the arteries) caused by vasodilation
Vasodilation
Vasodilation refers to the widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large arteries, smaller arterioles and large veins. The process is essentially the opposite of vasoconstriction, or the narrowing of blood vessels. When...
(broadening of the blood vessels) in the lungs of patients with liver disease
Liver disease
Liver disease is a broad term describing any single number of diseases affecting the liver.-Diseases:* Hepatitis, inflammation of the liver, caused mainly by various viruses but also by some poisons , autoimmunity or hereditary conditions...
. Dyspnea and hypoxemia are worse in the upright position (which is called platypnea
Platypnea
In medicine, platypnea refers to shortness of breath that is relieved when lying down, and worsens when sitting or standing up. It is the opposite of orthopnea...
and orthodeoxia, respectively).
Diagnosis
The hepatopulmonary syndrome is suspected in any patient with known liver disease who reports dyspnea (particularly platypnea). Patients with clinically significant symptoms should undergo pulse oximetryPulse oximetry
Pulse oximetry is a non-invasive method allowing the monitoring of the oxygenation of a patient's hemoglobin.A sensor is placed on a thin part of the patient's body, usually a fingertip or earlobe, or in the case of an infant, across a foot....
. If the syndrome is advanced, arterial blood gas
Arterial blood gas
An arterial blood gas is a blood test that is performed using blood from an artery. It involves puncturing an artery with a thin needle and syringe and drawing a small volume of blood. The most common puncture site is the radial artery at the wrist, but sometimes the femoral artery in the groin or...
ses should be measured on air.
A useful diagnostic test is contrast echocardiography
Echocardiography
An echocardiogram, often referred to in the medical community as a cardiac ECHO or simply an ECHO, is a sonogram of the heart . Also known as a cardiac ultrasound, it uses standard ultrasound techniques to image two-dimensional slices of the heart...
. Intravenous microbubbles (> 10 micrometers in diameter) from agitated normal saline that are normally obstructed by pulmonary capillaries (normally <8 to 15 micrometers) rapidly transit the lung and appear in the left atrium
Left atrium
The left atrium is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the mitral valve.-Foramen ovale:...
of the heart within 7 heart beats. Similarly, intravenous technetium
Technetium
Technetium is the chemical element with atomic number 43 and symbol Tc. It is the lowest atomic number element without any stable isotopes; every form of it is radioactive. Nearly all technetium is produced synthetically and only minute amounts are found in nature...
-99m–labeled albumin
Albumin
Albumin refers generally to any protein that is water soluble, which is moderately soluble in concentrated salt solutions, and experiences heat denaturation. They are commonly found in blood plasma, and are unique to other blood proteins in that they are not glycosylated...
may transit the lungs and appear in the kidney and brain. Pulmonary angiography may reveal diffusely fine or blotchy vascular configuration. The distinction has to be made with an intracardiac right-to-left shunt
Right-to-left shunt
A right-to-left shunt is a cardiac shunt which allows blood to flow from the right heart to the left heart. This terminology is used both for the abnormal state in humans and for normal physiological shunts in reptiles...
.
Disease mechanism
The hepatopulmonary syndrome results from the formation of microscopic intrapulmonary arteriovenous dilatations in patients with both chronic and acute liver failureLiver failure
Acute liver failure is the appearance of severe complications rapidly after the first signs of liver disease , and indicates that the liver has sustained severe damage . The complications are hepatic encephalopathy and impaired protein synthesis...
. The mechanism is unknown but is thought to be due to increased hepatic production or decreased hepatic clearance of vasodilators, possibly involving nitric oxide.
The vascular dilatations cause overperfusion relative to ventilation, leading to ventilation-perfusion mismatch and hypoxemia. There is an increased alveolar
Pulmonary alveolus
An alveolus is an anatomical structure that has the form of a hollow cavity. Found in the lung parenchyma, the pulmonary alveoli are the dead ends of the respiratory tree, which outcrop from either alveolar sacs or alveolar ducts, which are both sites of gas exchange with the blood as well...
-arterial partial pressure
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
of oxygen gradient
Gradient
In vector calculus, the gradient of a scalar field is a vector field that points in the direction of the greatest rate of increase of the scalar field, and whose magnitude is the greatest rate of change....
while breathing room air. Additionally, late in cirrhosis, it is common to develop high output failure, which would lead to less time in capillaries per red blood cell, exacerbating the hypoxemia.
Treatment
Currently the only definitive treatment is liver transplantation. Alternative treatments such as supplemental oxygenOxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
or somatostatin
Somatostatin
Somatostatin is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G-protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones.Somatostatin...
to inhibit vasodilation remain anecdotal.