HPS - Alaa Hassib

7/29/2019 HPS - Alaa Hassib

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Hepatopulmonarysyndrome

(HPS)By Alaa Haseeb , MS.c


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Definition:

HPS is a disease process with a triad of:1- Liver disease.2- Widespread intrapulmonary

vasodilatation.3- Gas exchange abnormality presentingwith increased alveolar arterial oxygen

gradient (P(A-a)O2) while breathingroom air, that results ultimately inhypoxemia.


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Prevalence:

Studies on HPS report a wide range ofprevalence of the disease which can bedue to different patient groups and study

designs. Usually it is reported to bebetween 9 to 29% of patients with liverdisease.


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Pathophysiology:

I) Vasodilatation:

Persistent pulmonary and systemicvasodilatation is mostly explained by the

imbalance of vasodilator and vasoconstrictoragents favoring vasodilators. This could be dueto:

a- Overproduction of the vasodilators from injured

hepatobiliary system.b- Decrease in their clearance by the liver.

c- Production of a vasoconstrictor inhibitor.


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d- Normal sensitivity of the pulmonary vessels tovasoconstrictors in response to hypoxemia isblunted in HPS.

- Numerous vasodilators are suspected but nitricoxide ( NO) is the most appreciated one. Othermediators include vaso-active intestinal peptide(VIP), calcitonin related peptide, glucagon,substance P and platelet activating factor.


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II) Hypoxemia:

- The main pathophysiologic event underlyinghypoxemia is widespread pulmonary precapillary

and capillary vasodilatation. Pulmonary capillarydiameter is normally about 8-15 micrometer(m) and this could rise up to 500 m in HPS.

- In addition, there is distinct arterio-venous (AV)malformations and direct AV communications.

- Pleural spider angiomas may also form.


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These changes lead to the following:

a- Ventilation perfusion ( V/Q) mismatch:

- Results from widespread pulmonary

vasodilatation and decreased V/Q ratioin alveolar-capillary units leading to lowpressure of oxygen in arterial blood ( PaO2) andlow oxygen (O2) content of the blood leaving

these units. This hypoxemia is correctable bybreathing 100% oxygen.


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b- Right to left shunting of the blood:

This results from direct arterio-venouscommunications that have no contact withbreathed air. If numerous, they can giverise to severe hypoxemia unresponsive tobreathing 100% oxygen.


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c Diffusion impairment:

Excessive vasodilatation causes O2molecules not to reach the center of

dilated capillaries readily. Increasedcardiac out put and decreased transitiontime of blood through pulmonary vascularbed on the other hand impairs diffusion,this is called diffusion-perfusion defectoralveolar capillary oxygen disequilibrium.


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d- Response to breathing 100% O2 :

- In response to breathing 100% oxygen if PaO2rose to levels 600mmHg, shunting of blood is

unlikely.- If it failed to exceed 500 mmHg, shunt can't beruled out.

- If it didn't rise to levels above 150-200mmHg,

shunt is most probably the main mechanism ofhypoxemia.


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Clinical Manifestations:

- More than 80% of patients present withsymptoms and signs of liver disease.

- In less than 20%, the presenting

symptoms and signs are related to lungdisease. These include dyspnea, cyanosis,clubbing, platypnea and orthodeoxia.

- There is controversy on a correlationbetween the severity of liver disease andHPS.


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Some studies have shown that the severerthe liver disease the severer the HPS, butothers have failed to show so.

- Mortality is high among HPS patients andis reported to be around 40% within 2-3years after presentation. Curious enough ,the causes of mortality are mostcommonly non respiratory (e.g., GIbleeding, sepsis, renal failure).


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DIAGNOSIS

Diagnostic criteria for HPS are

1) Liver disease, and

2) Gas exchange abnormality manifested byhypoxemia (PaO2< 70 mmHg) and/orP(A-a)O2>20mmHg due to widespreadintrapulmonary vasodilatation, inthe absence of any primarycardiopulmonary disease.


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Diagnostic Procedures:

a) Arterial blood gas analysis:

Performed in the supine and sitting

positions.

b) Chest X-rayand chest CT:

Are normal or show non-specific minorreticulonodular changes in the base of

the lungs and /or dilatation of theperipheral pulmonary vasculature.


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c) Pulmonary function tests:

commonly show decreased diffusion ability of thelungs pointing to intrapulmonary vasodilatation.

d) Two dimensional contrast enhancedechocardiography (CEEC):

Is the method of choice for diagnosingintrapulmonary vasodilatation and is the mostsensitive procedure designed for this purpose.


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CEEC , however, lacks specificity in that inchronic liver disease the prevalence ofpulmonary vasodilatation is about 20% by

this method despite normal gas exchangestatus. Contrast enhanced trans-esophageal echocardiography is more

sensitive than trans-thoracicechocardiography, and correlates morewith gas exchange abnormality.


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e) Macro aggregated albuminscanning:

Technetium 99m- labeled macroaggregated

albumin is used. The estimated sensitivityof this method for diagnosingintrapulmonary vasodilatation is about

84% and its specificity is 100%. Inaddition, shunt fraction can be calculatedby this procedure.


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f) Pulmonary angiography:

Two different angiographic patterns in HPS:

Type I:more common. There are minimalchanges with diffuse spider like branchesto more advanced changes with a blotchy,spongy appearance ( the type thatresponds to breathing 100% oxygen).


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Type II: less common. There are vascularlesions as vascular dilatations representing

A-V communications ( the type that

responds poorly to breathing oxygen andliver transplantation is not as suitable asfor type I vascular lesions).

g) Pulmonary artery catheterization:

Is not used commonly for diagnosing HPS.


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Treatment:

I) Medical therapy:

There are currently no medications proved tohave persistent, adequate or acceptable effect

on HPS. The following are tried:a- Almitrin bimesylate:is a stimulator of arterial

chemoreceptors ( used in COPD).

b- Indomethacin:To cause inhibition of prostaglandin production

which has a putative role of vasodilatation.


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c- Methylene blue:

Is a potent inhibitor of NO and itsintracellular mediator, gunaylate cyclase

and is potentially effective for treatment ofHPS although transiently. It might be usedin the post-operative period of livertransplantation in cases with transienthypoxemia, however its routine and longterm use is not recommended yet.


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II) Interventions other than livertransplantation:

a- Embolotherapy:

It is recommended that pulmonary angiographybe done for HPS patients who respond poorly tobreathing 100% oxygen i.e., PaO2


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b- Portal decompression wtihtransjugular intrahepatic

portosystemic shunt (TIPS):

There is controversy regarding thebeneficial effects of this technique on HPS.Some studies confirmed the improvementof hypoxemia and others ruled out anyusefulness of TIPS. More researches areneeded undoubtfully.


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III) Orthotopic Liver transplantation(OLT):

Previously, hypoxemia was considered as

an absolute contraindication for OLT.Today the trend is to give a chance to thisgroup of patients with the logic that HPSis a progressive and fatal disease andthere isn't an effective therapy whichcould improve oxygenation significantly.


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The rate of improvement of HPS patientswith type I vascular lesions undergoingOLT is about 80% , but is much less in

those with type II lesions.


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Thank you

Alaa Haseeb , MS.c

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HPS - Alaa Hassib