As mentioned earlier, portal hypertension is defined by pressure measurements : specifically the gradient between portal and caval pressures ( the portal pressure gradient ) .
The normal value for the portal pressure gradient is 2 to 6 mm Hg. If this gradient is more than 10 mm Hg then clinically significant portal hypertension is present.
Varices are rarely seen if the gradient is less than 10 mm Hg.
Variceal bleeding is not observed if the pressure gradient is less than 12 mm Hg.
Most Importantly , protection from variceal bleeding is gained if the pressure gradient is less than 12 mm Hg.
The direct measurement of this value is invasive .
The most frequently adopted method involves Transjugular Catheterization.
The advantage of this procedure is that both caval and hepatic venpus pressures maybe measured during the same procedure.
Less frequently , a transhepatic approach is adopted and rarely , direct surgical measurements are used.
These less frequently used methods only measure absolute portal pressures and a second measurement of caval pressure is still needed to calculate the gradient.
Because of the invasiveness of this technique, it is only used intra operatively during surgery for portal hypertension.
Indirect measurements can also be used for assessment of portal pressure gradient.
This procedure involves measurement of the free and wedged hepatic venous pressure using catheterization of the right hepatic vein.
Wdged hepatic venous pressure measusred using a balloon tipped catheter reflects the pressure in the static column of blood from the hepatic vein to the sinusoid.
It is an assessment of sinusoidal pressure rather than portal venous pressure .and therefore may under estimate the portal pressure gradient in diseases characterized by presinusoidal hypertension.
The Free Hepatic Venous Pressure is obtained with the catheter in the hepatic vein and gives an assessment of caval pressure.
Free hepatic venous pressure is not elevated in patients with diseases characterized by pre sinusoidal and sinusoidal portal hypertension but it is characteristically in states of hepatic outflow block such as Budd Chiari syndrome.
The Gradient between the two measurements is called as Hepatic venous Pressure gradient and is the most commonly quoted parameter in the medical literature regarding management of portal hypertension.
Both the absolute value of hepatic venous pressure gradient and the change in hepatic venous pressure gradient with pharmacotherapy have prognostic significance related to the risk of variceal bleeding.
The splenic pupl pressure is a useful parameter in diseases with predominantly pres inusoidal portal hypertension when as mentioned earlier , wedged hepatic venous pressure under estimates portal pressure.
It can be appreciated that ven indirect methods of measuring portal pressure are not readily available in most settings .
Instead, most clinicians rely on the clinical manifestations of portal hypertension : Esophageal varices, Splenomegaly , Oedema and Ascites
Free Hepatic Venous Pressure : FHVP
The baseline intravascular pressure recorded in an un occluded hepatic vein.
It is the pressure measured inside a hepatic vein when a catheter tip is positioned freely in the blood stream.with the balloon deflated.
It reflects systemic venous pressure and is close to the pressure in the Inferior vena cava.
Role in Calculation :
FHVP is subtracted from Wedged Hepatic Venous Pressure WHVP to determine the Hepatic Venous
Pressure Gradient HVPG
HVPG =WHVP-FHVP
Normal Values :
A normal HVPG is less than 5 mmHg.
An HVPG value greater than 5 mmHg indicates portal Hypertension and a value greater than 10 mm Hg is considered clinically significant.
Procedure Context :
It is measured during a minimally invasive hepatic venous catheterization often via the internal jugular veinwhich serves as the Gold Standard for evaluating Chronic Liver Disease and Portal Hypertension
Causes of Raised Free Hepatic Venous Pressure / FHVP :
Budd Ciari Syndrome ,Constrictive Pericarditis, Inf Vena Caval Obstruction , Congenital Inferiors Vena Caval Web & Right Heart Failure
Wedged Hepatic Venous Pressure:
The static pressure measured in a hepatic vein when a balloon tipped catheter is inflated to occlude the vessel. Serving as an indirect estimate of pressure within the liver sinusoids and portal venous system.
Is not measued in isolation. Doctors subtract the free hepatic venous pressure measured with balloon deflated in the open hepatic vein from WHVP to find the Hepatic Venous Pressure Gradient
HVPG = WHVP – FHVP
Normal HVPG is less than 5 mm Hg
Portal Hyprtension > 5 mm Hg
Clinically Significant Portal Hypertension > or equal to 10 mm Hg. Indicated risk for clinical decompensation , ascites or esophageal varices.
Severe Portal Hypertension :
More than 20 mm Hg indicates High Risk of Variceal Bleding and Mortality.
How is measurement done :
A catheter is inserted via Right Internal Jugular Vein and navigated down the Inferiors Vena Cava into a hepatic ven using fluoroscopic guidance
HVPG : Hepatic Venous Pressure Gradient :
Is the Gold Standard diagnostic & Prognostic Measurement used to evaluate Portal Hypertension in Chronic Liver Disease
HVPG = WHVP – FHVP
Wedged Hepatic Venous Pressure – Free Hepatic Venous Pressure
Normal Value : 1 – 5 mm Hg
Portal Hypertension : More than 5 mmHg
Clincally significant Portal Hypertension : Moe than 10 mm Hg, and high risk of complications like Ascites & Varices
Severe / High Risk of bleeding > 12 mm Hg
And critical risk of variceal rupture or > 20 mm Hg High Risk Mortality.
Clinical Utility :
Risk Stratification :
Assess the severity of Liver Cirrhosis and Fibrosis.
Treatment Monitoring :
Measure the effectiveness of medications such asnon-selective beta blockers . A successful therapeutic
response is defined as and HVPG reduction of more than 20 % or a drop to less than 12 mm Hg.
Surgical Planning : Helps determine if patients with Hepatocellular ca can safely undergo Liver resection.
Causes of Raised HVPG :
Cirrhosis
Alcoholic Hepatitis
Haemochromatosis
Infiltrative Liver Disesae
Acute Fatty Liver of Pregnancy
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