Post on 31-May-2015
Hepatopulmonary syndrome is considered present when the following triad exists
Liver disease Impaired oxygenation Intrapulmonary vascular abnormalities,
referred to as intrapulmonary vascular dilatations (IPVDs)
Failure of damaged liver to clear circulating pulmonary vasodilators
Production of circulating vasodilator by damaged liver
Inhibition of circulating vasoconstrictive substance by damaged liver
Key priming factor : Increased endogenous NO production
Possible Mediators of Vascular Dilatation in HPS
Increased Pulmonary Vasodilators
Prostaglandin I2 or E1
VIP
Nitric oxide
Platelet-activating factor
Decreased Vasoconstrictors
Endothelin
Tyrosine
Serotonin
Clinical Features
Dyspnoea
Spider nevi
Clubbing
Cyanosis
Severe hypoxaemia
Orthodeoxia
Platypnoea
Clinical features
Platypnea –Increase in dyspnea that is induced by moving into an upright position and relieved by recumbency
Orthodeoxia – Decrease in the arterial oxygen tension (by > 4 mmHg) or arterial oxyhemoglobin desaturation (by > 5%) when the patient moves from a supine to an upright position, which is improved by returning to the recumbent position
It is hypothesized that platypnea and orthodeoxia are caused by preferential perfusion of IPVDs in the lung bases when the patient is upright
Hypoxemia is due to intrapulmonary vascular dilatations which range in diameter from 15 to 160 microns
Shunting through the IPVDs leads to ventilation-perfusion mismatch & oxygen diffusion limitation
Ventilation-perfusion mismatch is a consequence of increased blood flow through the IPVDs in the setting of preserved alveolar ventilation
Results in the passage of mixed venous blood into the pulmonary veins
The oxygen diffusion limitation is a consequence of diffusion-perfusion impairment
At room air, the partial pressure of O2 is insufficient for equilibration with blood moving near the center of the alveolar capillary because of the increased diameter of the IPVDs
Supplemental oxygen increases the driving pressure of O2 & improves oxygenation, which distinguishes IPVDs as physiologic rather than anatomic shunts
ABG analysis : pt sitting in upright posture
PaO2 : <80 mmHgSensitive measure
Elevated alveolar-arterial (A-a) oxygen gradient
Defined as ≥15 mmHg when breathing room air
Contrast-enhanced echocardiography: more sensitive , less invasive
Technetium-99m-labeled macro aggregated albumin scanning
Pulmonary arteriography
Performed by injecting agitated saline or indocyanine green dye intravenously
Normally the contrast opacifies only the right heart chambers because it is filtered by the pulmonary capillary bed
Contrast may opacify the left heart chambers if a right-to-left intracardiac or intrapulmonary shunt is present
Intracardiac shunt : contrast appears in the left heart within 3 heart beats after injection
Intrapulmonary shunt : contrast generally appears in the left heart 3 to 6 heart beats after its appearance in the right heart
It involves intravenously injecting albumin macroaggregates that should be trapped in the pulmonary capillary bed, since the 20 micron diameter of the macroaggregates exceeds the normal pulmonary capillary diameter of 8 to 15 microns
Scans that identify uptake of the radionuclide by the kidneys and/or brain suggest that the macroaggregates passed through either an intrapulmonary or intracardiac shunt
The proportion of radionuclide taken up may be used to quantify the shunt
Limitation Inability to distinguish intrapulmonary from intracardiac
shunts lower sensitivity
Two patterns of IPVD:
TypeⅠor diffuse pattern▪ Minimal typeⅠ : normal vessels or diffuse and tenuous spider
web vascular abnormalities▪ Advanced type : a spongy or blotchy appearanceⅠ
TypeⅡ or focal pattern: arteriovenous malformations
CXR may show increased bibasilar interstitial marking
Spirometry : normal
Long term oxygen therapy
Transjugular intrahepatic portosystemic shunt (TIPS) placement has been associated with improvement of HPS in several case reports
Liver transplantation is indicated for patients with incapacitating hypoxemia due to HPS
Normalization of the abnormal oxygenation Require up to 15 months
• HPS is characterized by defects in oxygenation due to pulmonary abnormalities associated with chronic liver disease.
• Dyspnea and hypoxemia can be severe and often worsen in the upright position.
• Gross dilatation of the precapillary and capillary vessels occurs with ventilation–perfusion mismatch.
• The syndrome usually improves after liver transplantation.