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.