Portal HTN Flashcards
What is portal hypertension and why does it develop?
Because of increased resistance to portal blood flow through the liver causing high blood pressure in the portal system
What are the 3 categories of portal HTN?
Prehepatic
Intrahepatic
Posthepatic
Does the portal vein account for half, or 2/3rds of hepatic blood flow?
2/3rds
What is the strict definition of portal HTN?
absolute increase in the blood pressure within the portal vein > 8mmHg
OR
increase in the pressure gradient between the portal vein and hepatic vein of 5 mmHg or more
How is pressure in the portal vein assessed?
Doppler ultrasound
What are the major posthepatic causes of portal HTN?
Severe right-sided heart failure (and other causes of vena cavae obstruction)
Restrictive pericarditis
Budd-Chiari syndrome (thrombosis of the hepatic veins)
What Is the major intrahepatic cause of portal HTN?
Cirrhosis
What are the major causes of prehepatic portal HTN?
Thrombosis of the portal vein/splenic vein (due to hypercoaguable states and malignancy, eg pancreatic cancer)
Narrowing of the portal vein before it ramifies within the liver
Massive splenomegaly with increased splenic vein blood flow
What is the most important and frequent cause of portal HTN?
Cirrhosis
What are the minor causes of intrahepatic portal HTN?
Shistosomiasis (presinusoidal portal HTN)
Massive fatty change
Sarcoidosis (and other diffuse fibrosing granulomatous diseases)
Diseases affecting portal microcirculation (eg, nodular regenerative hyperplasia)
How is the resistance to portal flow increased at the level of the sinusoids in portal HTN?
Contraction of vascular smooth muscle and myofibroblasts
Disruption to normal flow by scarring and nodules of parenchymal regeneration
How do intrahepatic endothelial cells contribute to intrahepatic portal HTN?
Vasoconstrict through decrease in NO production
Release of endothelin-1, angiotensinogen and eicosanoids
How does the arterial system of the liver worsen intrahepatic portal HTN, especially in cirrhosis?
Arterial and portal systems in the liver anastamose
These intrahepatic shunts in fibrous septa load arterial pressure into the low pressure portal venous system
Also negatively affect metabolic exchange between sinusoidal blood and hepatocytes
How would you describe splanchnic circulation in portal HTN?
Hyperdynamic (fast flow rate)
Why does splanchnic circulation change in portal HTN?
NO production causing arterial vasodilation
Stimulated by reduced bacterial DNA clearance due to mononuclear phagocyte function decreasing
Also because of intrahepatic arterial-portal shunting bypassing Kupffer cell populations
Are antibiotics possibly effective in some treatments of portal HTN?
Yes
Bacteria are thought to contribute to splanchnic hyperdynamic flow
What are the four major complications of portal HTN?
Ascites
Formation of portosystemic shunts
Congestive splenomegaly
Hepatic encephalopathy
What is the term for accumulation of fluid in the peritoneal cavity?
Ascites
What percentage of ascites cases is caused by cirrhosis?
85%
What is the concentration of protein in ascites fluid?
It’s mostly serous
<3g/dL
T/F the solute concentrations (sodium, potassium, glucose) in ascites fluid is less than that of blood
False
Usually close to serum levels
Are cells common in ascites fluid?
No
Sometimes a small amount of WBCs
What does the presence of RBCs in ascites fluid usually mean?
Possible disseminated intra-abdominal cancer
What is a complication of long standing ascites?
Seepage into transdiaphragmatic lymphatics
Produces hydrothorax, more often on the right side
What are the three aetiologies of ascites?
Sinusoidal hypertension causing fluid to move into the space of Disse which is then removed by hepatic lymphatics (made worse by hypoalbuminaemia)
Percolation of hepatic lymph into the peritoneal cavity
Splinchnic vasodilation and hyperdynamic circulation caused by HR and CO unable to maintain BP when splanchnics dilated which activates RAAS -> HTN, vasodilation, Na and water retention increases perfusion pressure -> extravasation of liquid into abdomen
How does hepatic lymph contribute to ascites?
Normal thoracic duct lymph flow is 800-1000mL/day
Cirrhosis can increase demand on thoracic duct flow to 20L/day, exceeding capacity
Where do portosystemic shunts form in theory?
Where systemic and portal circulation share common capillary beds
What are common places for portosystemic shunts?
Rectum
Oessophagogastric junction
Retroperitoneum
Falciform ligament of the liver (involving periumbilical and abdominal wall collaterals)
Are portosystemic shunts in the rectum/anus clinically important?
No
Haemorrhoidal bleeding may occur, but is not usually massive or life-threatening
How do abdominal wall portosystemic shunts appear clinically?
‘Caput medusae’
Dilated subcutaneous veins extending from the umbilicus toward the rib margins
Important clinical sign of portal HTN
Are oesophageal varices important clinically?
Critically important
How often do oesophageal varices occur in patients with cirrhosis?
40% of patients
What is the major complication of oesophageal varices?
Rupture
Massive haematemesis and loss of blood
Hypovolaemia
Death
How quickly do patients destabilise when oesophageal varices rupture?
Very quickly – minutes to hours
What is the mortality rate of oesophageal varices?
30%
What is the hepatic venous pressure gradient (HVPG)?
The difference in pressure between the portal vein and the IVC
What is the wedged hepatic venous pressure (WHVP)?
The pressure in a hepatic vein
Can be used to estimate portal pressure because blood hits the balloon in the hepatic vein branch and the static column of blood transmits approximately the portal pressure directly to the balloon
What is the free hepatic vein pressure (FHVP)?
IVC pressure
Used as a baseline
How is HVPG (hepatic venous pressure) calculated?
WHVP - FHVP
Portal pressure minus normal IVC pressure, essentially
What is the normal HVPG pressure range?
3-6 mmHg
What is the definition of portal HTN in terms of actual pressure?
HVPG > 8 mmHg
HVPG > 12 mmHg is the threshold for the potential formation of varices, and higher levels increase risk for variceal haemorrhage
How can ascites be classified?
Peritoneal or non-peritoneal
How is the serum-ascites albumin gradient (SAAG) used in differentiating ascites classifications?
Nonperitoneal diseases produce ascites with a SAAG greates than 1.1 g/dL
What are some causes of nonperitoneal ascites?
Intrahepatic and extrahepatic portal HTN
Hypoalbumaemia (nephrotic syndrome)
Myxoedema
Ovarian tumours
Pancreatic or biliary ascites
Chylous ascites (obstruction of thoracic duct or cisterna chyli)
What are the causes of chylous ascites?
Mostly due to malignancy (eg lymphoma)
Can be seen post-operatively and following radiation injury
What are some causes of peritoneal ascites?
Malignancy (primary peritoneal mesothelioma)
Granulomatous peritonitis
Vasculitis (SLE, Henoch-Schonlein purpura)
Whipple disease
Endometriosis
What are 4 causes of granulomatous peritonitis?
TB
Fungal and parasitic infections (Candida, Cryptococcus, Schistosoma)
Sarcoidosis
Foreign bodies (talc, cotton, barium)
Is massive ascites that does not respond to treatment a prognostic factor?
Yes
50% patient mortality within 6 months in patients exhibiting this feature
