Liver anatomy and blood supply

Question 1

What percentage of CO does the liver receive at rest

Answer 1

25% - approximately 1500 ml/minute

Question 2

Describe the blood supply to the liver

Answer 2

Celiac artery –> RIGHT AND LEFT HEPATIC ARTERIES

• Contribute 1/3 blood supply to the liver (500 ml/min)
• But supply nearly 50% of the O2 (as this blood is fully oxygenated)

PORTAL VEIN
- Contributes 2/3 blood supply to liver (100ml/min)

Question 3

What is the meaning of the word ‘portal’ in portal vein?

Answer 3

The term portal refers to a vein that connects to capillary systems. Blood in the portal vein flows between the capillary networks of the abdominal organs (intestines / stomach / spleen / pancreas ) and the liver.

Question 4

What is the SaO2 of blood in the portal vein?

Answer 4

During fasting ± 85%

Fed state ± 70%

Question 5

Classify the regulation of hepatic blood flow

Answer 5

INTRINSIC and EXTRINSIC MECHANISMS

Question 6

Describe the intrinsic mechanisms that regulate hepatic blood flow.

Answer 6

INTRINSIC MECHANISMS

Hepatic arteries:
- Autoregulation in hepatic arteries that fails below 60 mmHg maintaining flow despite MAP.

Portal vain

• Minimal vascular smooth muscle cannot vasoconstrict
• Instead blood flow is proportional to the pressure gradient in the portal vein.

There is a SEMI-RECIPROCAL relationship between the portal veins and hepatic arteries
1. Portal vein blood flow falls –> compensatory vasodilation in hepatic arteries to increase hepatic blood flow.

2. Hepatic artery blood flow falls –> portal vein cannot compensate

Question 7

Describe the extrinsic mechanisms that regulate hepatic blood flow

Answer 7

SNS innervates hepatic arteries and the portal vein

SNS –> VC in hepatic arteries
SNS –> Increased tone in portal vein, venules and hepatic veins. Capacitance system ‘squeeze’ –> return of 250 ml to circulation. This along with ‘squeeze’ splanchnic capacitance vessels –> return of approximately 1000 mls of blood to circulation.

Question 8

How does the respiratory cycle and positive pressure ventilation affect hepatic venous flow?

Answer 8

Spontaneous breathing

Inspiration - negative intrathoracic P –> increase hepatic venous blood flow

Expiration - positive intrathoracic pressure –> decrease hepatic venous flow

IPPV + PEEP –> decrease hepatic venous blood flow.

Question 9

Describe the intra-operative anaesthetic and surgical factors that affect hepatic blood flow.

Answer 9

Anaesthetic factors:

1. IPPV and PEEP –> decrease HBF
2. Volatiles and vasopressors –> decrease HBF
3. Ve: Hypocapnoea –> reduced HBF
4. Ve: Hypercapnoea –> increased HBF
5. Neuraxial anaesthesia –> decreased HBF

Surgical factors:
Liver retraction/packing reduces hepatic blood flow significantly more than any of the above anaesthetic factors

Question 10

Describe the morphological anatomy of the liver

Answer 10

Based on the external appearance of the liver –> not useful for hepatobiliary surgery (see functional anatomy)

Right lobe (very large) separated from Left lobe by the falciform ligament. On the undersurface two more lobes are observed: the caudate lobe (posterior) and the quadrate lobe (inferior).

Question 11

Describe the functional anatomy of the Liver and the name of the classification used

Answer 11

The Couinaud classification

• Divides the liver into eight functionally independent lobes.
• Each lobe has its own:
• -> branch hepatic a.
• -> branch portal v.
• -> hepatic venous drainage
• -> biliary drainage
• Segments are numbered 1 to 8 in a clock wise direction starting with the caudate lobe.

Question 12

What is the name of the point where the portal vein, common bile duct and hepatic artery enter the liver

Answer 12

Porta hepatis or the hilum