Liver & Anaes

Question 1

Anatomy of Liver

Answer 1

There are hexagonal hepatic lobules in the liver and at the end we have the portal triad (portal vein, portal artery, and bile duct) and the hepatocytes stretch from the portal triad to the central vein of these hexagonal
lobules. The lobules that are nearest your portal triad, get the most oxygen and the ones that are nearest the central vein will have the lowest oxygen tension and thus the highest risk for ischaemic necrosis.

If close to central vein, then  risk of ischaemic necrosis

Question 2

We divide the hepatocytes into different zones:

Answer 2

• Zone 1  nearest to the hepatic triad & thus most resistant to ischaemia as it has the
  highest oxygen concentrations
• Zone 3  nearest to the central vein & thus has the highest risk of / is most susceptible
  to ischaemia as it has the lowest oxygen concentration

Question 3

Blood supply to the liver

Answer 3

The liver has a two-fold supply, but they are not equal. The arteries supply about 30% of the blood supply but it supplies about 50% of the oxygen (higher oxygenation). The hepatic portal vein has already given off some oxygen to the GIT by the time it flows to the liver  it supplies 70% of the blood supply, and 50% of the oxygen (lower oxygenation)

Question 4

Describe autoregulation and the liver’s blood supply *

Answer 4

Autoregulation decreases during fasting
The hepatic artery has alpha and beta receptors
it can compensate by increasing its flow if there is a decrease in flow in the portal vein.
The problem with this is that a decrease in hepatic blood flow, will not result in an increased portal blood flow. So risk of ischemia if decrease in BP

Because there is both alpha & beta receptors in your hepatic artery, we can cause both vasoconstriction and vasodilatation
the hepatic portal vein only has alpha receptors and thus there is no vasodilation only constriction.

Sympathetic stimulation will thus affect both blood flows. Sympathetic has both an alpha and beta effect but the alpha effect tends to have a bigger effect on the blood flow because it tends to affect both blood supplies, and this will lead to a decreased blood flow in your liver

Question 5

Effect of anaesthesia on the liver

Answer 5

• As your PaCO2 increases, your sympathetic stimulation will increase, and this will lead to an increase in splanchnic vascular resistance (due to alpha receptors)
• When you give IPPV +- PEEP, you get an increase in venous pressure which will decrease your blood flow, on top of that, you may get a decrease in cardiac output
• decr blood flow and oxygenation of liver

Question 6

IAA and liver blood flow

Answer 6

The best agent to use is sevoflurane and the worst agent to use is halothane *** See graph!

Question 7

IAA metabolism:

Answer 7

• Cytochrome P450 proteins in the liver
  o Halothane is 20%
  o Isoflurane 0.2%
  o Sevoflurane 3%
  o Desflurane <0.02%
• Enzyme-inducing drugs will increase metabolism
• Halothane-hepatitis in 20% of people

Question 8

Halothane-hepatitis pathophysiology

Answer 8

Immune mediated
- Antibodies are generated to trifluoracetyl-moiety (metabolite of Halothane)
- Antigen and antibodies are found in patients with Halothane-hepatitis

Question 9

Halothane-hepatitis clinical findings

Answer 9

o Malaise
o Delayed pyrexia
o Jaundice
o Eosinophilia
o Markedly abnormal LFT’s

Question 10

High risk group for Halothane-hepatitis

Answer 10

• Familial  avoid if family history
• More in women
• Obesity  be careful in obese women
• Multiple halothane anaesthetics  do not give repeat halothane within 8 weeks
• Hypersensitivity  avoid with enzyme-inducing treatment
• Hypoxia