HPB / hepatology Flashcards
What is the normal metabolism of ammonia?
Liver normally metabolises ammonia.
- 50% of ammonia arises from endogenous glutamine conversion in enterocytes. 50% is from the gut lumen by degradation of nitrogen substrate from diet or gut bacteria.
In hepatocytes ammonia is converted yo urea or glutamine.
Why does ammonia rise in liver failure?
The loss of viable hepatocytes leads to impaired metabolism of ammonia
What effects do raised ammonia have?
- It accumulates in astrocytes which can lead to hepatic encephalopathy, cerebral oedema, intracranial hypertension and brain herniation.
- It also contributes to immune dysfunction and infection
What’s the prognostic value of ammonia?
> 150 in ALF is associated with increased complications
In ACLF the risk of cerebral oedema is lower but raised ammonia is a/w increased risk of extra-hepatic organ failure and death.
How to measure ammonia?
Arterial samples better reflect acute changes in nitrogen metabolism.
Sample needs to be fresh.
Serial measurements are more useful that a single time point
What are the potential therapeutic strategies to modulate serum ammonia?
- Lactulose
- Rifaximin
- Metabolic scavengers e.g. LOLA
- RRT
- Liver support dialysis e.g MARS
- Plasma exchange
What are the mechanisms of action of lactulose in managing ammonia?
- Colonic acidification promotes conversion of NH3 (ammonia) to non-absorbable NH4+ (ammonium)
- Inhibits ammoniagenic bacteria growth
- Inhibition of intestinal glutamine absorption
- Decreased ammonia absorption time and increased nitrogen excretion
What is the pathophysiology of portal hypertension?
- Developes due to resistance in the portal venous system due to functional and structural alterations
- In response to injury liver sinusoidal cells become capillarised
- extracellular matrix gets formed and fibrogenesis occurs
- Myofibroblast contraction and decreased vasodilators e.g. NO
- These all result in increased resistance
What circulatory changes does PH lead to?
- splanchnic vasodilatation
- neurohormonal disturbances
- systemic vasodilatation
- reduced MAP
=hyperdynamic state
In addition alterations to the gut microbiome, increased gut permeability and systemic infl act as both perpetrators and precipitants of worsening portal hypertension
What is the splanchnic circulation?
The flow of blood to the abdominal organs including stomach, liver, pancreas and intestines
How do varices develop?
- PH results in reversal of flow and formation of alternative blood flow channels between the portal and systemic circulation
What do varices indicate about portal hypertension?
Signify clinically significant portal hypertension
What is the surrogate marker for PH?
HVPG >5mmHg
What HVPG signifies CSPH?
> 10mmHg
What are the risk factors for variceal haemorrhage?
- Larger varices ->5mm
- higher HVPG
- high grade of child class
- presence of red colour signs marking
- active alcohol consumption
- sepsis
How is variceal haemorrhage managed?
- judicious resus
- aim Hb 7-9
- correcting INR not warranted
- adequate purging of stomach to remove blood as a culture medium
- antibiotics and post bleed sepsis increases mortality and risk os high
- PPI
- Teripressin / octreotide for at least 2-5 days
- OGD and band ligation
What is the primary prevention of variceal haemorrhage?
Non-selective beta-blockers e.g. carvediolol
Why does ascites form in portal hypertension?
- PH results in backflow and accumulation of vasodilatory substances
- This results in intrahepatic vasoconstriction, peripheral dilatation and splanchnic vasodilation
- This circulatory changes result in hypoperfusion of the renal system
- State of relative hypovolaemia activates RAAS and SNS leading to salt and fluid retention - which causes an increased blood volume leading to filtration from the liver surfaces and mesenteric vessels
- increased hydrostatic pressure, decreased oncotic pressure and increased vasc permeability contribute to increased filtrations through mesenteric blood vessels which exceed the resorptive capacity of the peritoneum and lymphatics can’t counteract these mechanisms
How is ascites manages?
Salt restriction
Adequate calories and protein
Diuresis - furosemide and spiro
Terlipressin
Drainage
TIPSS
How does terlipressin help reduce ascites?
- increases renal perfusion, increases GFR and Na excretion, mobilises ascites
What raises AST?
Raised in hepatocellular injury and is also found in skeletal muscle and myocardium
What raises ALT?
Raised in hepatocellular injury.
What raises ALP?
Hepatobiliary -> biliary obstruction,nintrahepatic cholestasis, primary biliary cirrhosis, hepatocellular damage.
Bone -> healing #, metastatic tumour, Pagets, osteomalacia, physiological bone growth
Intestine -> intestinal infarction
Placenta -> normal pregnancy
Other -> sepsis, renal failure
What causes raised GGT?
- cholestatic, hepatocellular or infiltrative liver disorders
- chronic etoh
- prostate cancer