Pathophysiology of congestion & oedema

Question 1

What is congestion?

Answer 1

Relative excess of blood in vessels of tissue or organ

Question 2

Is congestion passive or active?

Answer 2

Passive

Question 3

Is congestion acute or chronic?

Answer 3

Acute or chronic

Question 4

Using the idea of Darcy’s law, what must happen in order for congestion to occur?

Answer 4

Blood flow = Pressure/resistance

Congestion (drop in blood outflow) will occur if the pressure gradient drops or resistance increases

Question 5

Congestion is quite a wide term and covers many examples

Give some pathological examples of congestion, and what causes them

Answer 5

Local acute congestion:
- Deep vein thrombosis

Local chronic congestion:
- Hepatic cirrhosis

Generalised acute congestion:
- Congestive cardiac failure

Question 6

What is local acute congestion?

Answer 6

Congestion due to something like DVT which blocks venous drainage

The main risks are ischaemia and infarction of the affected tissue

Question 7

Hepatic cirrhosis is an example of something that causes local chronic congestion

What is hepatic cirrhosis?

Answer 7

Fibrotic disease of the liver

Caused by severe damage to the liver, through alcohol abuse or Infection by HBV, Hep B, Hep C

Liver regenerates as nodules of hepatocytes with large areas of intertwining fibrosis

Question 8

Why does hepatic cirrhosis cause local chronic congestion?

Answer 8

Altered architecture alters blood flow through the liver, and blocks portal blood flow

This causes congestion in the portal vein and branches as the normal route for portal blood is blocked

Question 9

What risk is associated with local chronic congestion?

Answer 9

Haemorrhage

portal venous pressure very high because portal flow is blocked

Question 10

Hepatic cirrhosis causes local congestion in the portal vein and its branches

What happens to all this congested blood?

Answer 10

It flows through collateral branches (via anastomoses) and rejoins the systemic circulation

This causes the collateral vessels involved to dilate abnormally

These vessels can be visible around the umbilicus region and running up the oesophagus

Question 11

What is congestive heart failure?

Answer 11

Basically a build up of fluid in your body due to the heart being unable to effectively pump blood

Question 12

Describe how congestive heart failure actually causes congestion

Answer 12

Bad heart ∴ Cardiac output drops

CO drops ∴ Glomerular filtration rate (GFR) drops

GFR drops ∴ Renin-angiotensin-aldosterone system activated because the body thinks BP is too low

RAAs activation ∴ Na+ and H2O retained ∴ body fluid shoots up so fluid overload in veins n shit

Question 13

How is congestive heart failure treated?

Answer 13

Diuretics

Question 14

The effects of Congestive heart failure can be thought of as Right heart failure effects & left heart failure effects

What are the effects of left heart failure?

Answer 14

Left heart = receives blood from pulmonary circulation

LH failure ∴ blood dams back into lungs ∴ pulmonary oedema

Question 15

How can left heart failure be identified on examination?

Answer 15

Palpation - tachycardia

Auscultation - crepitations in lungs

Question 16

What are the effects of right heart failure?

Answer 16

Right heart = receives blood from systemic circulation

RH failure ∴ blood dams back into systemic circulation

Increased JVP
Hepatomegaly
Peripheral oedema

Question 17

What clinical signs on examination, would indicate right heart failure?

Answer 17

Inspection - increased JVP & peripheral oedema

Palpation - peripheral oedema & Hepatomegaly

Question 18

What risk does congestive heart failure pose to the liver?

Answer 18

Hepatic central venous congestion - ‘Nutmeg liver’

Question 19

Describe/explain the appearance of nutmeg liver

Answer 19

Nutmeg appearance due mixture of red/brown and pale groups of hepatocytes

Red = pericentral hepatocytes
- Poorly oxygenated due to stasis of blood

Pale = periportal hepatocytes
- Slightly better oxygenated due to proximity to hepatic arterioles

Question 20

Oedema is causes by an imbalance between the pressure moving fluid out of capillaries and the pressure moving fluid into capillaries

What pressures are these?

Answer 20

Hydrostatic pressure

Osmotic/oncotic pressures n all them

Question 21

Aside from pressures, what affects the amount/rate of fluid moving between capillaries and the interstitium?

Answer 21

Permeability characteristics of vessels

Area of endothelium

Question 22

What is oedema?

Answer 22

Accumulation of abnormal amounts of fluid in extravascular compartments

Extravascular Compartments can refer to intercellular tissue compartments (extracellular fluid) or to body cavities

Question 23

Oedema can mean fluid collecting in a body cavity

What is the name specifically for this?

Answer 23

Effusion

Effusions: fluid collections in body cavities

Pleural, pericardial, joint effusions
Abdominal cavity - ascites

Question 24

The fluid in oedema can either be exudates, or transudates

What are these?

Answer 24

Exudate:

• High protein/albumin content
• Related to inflammatory response, tumour or allergy which causes increased vascular permeability

Transudate:

• More watery
• Due to Cardiac failure / fluid overload = alterations of haemodynamic forces across capillary walls

Question 25

What happens in pulmonary oedema?

Answer 25

Left heart failure causes damming of blood back into pulmonary circulation

∴ pulmonary vascular pressure and volume increases

∴ Abnormally high hydrostatic outwards pressure

∴ Build up of TRANSUDATE

Question 26

Pulmonary oedema can eventually involve build up of transudate in the alveolar spaces

How does this occur?

Answer 26

Build up of perivascular & interstitial transudate

Progressive oedematous widening of alveolar septa

This allows transudate to accumulate in alveolar spaces

Question 27

Which is involved in peripheral oedema, transudate or exudate?

Answer 27

Transudate

Question 28

Give some examples of causes of oedema

Answer 28

Heart failure

Lymphatic blockage

Abnormal renal function

Hypoalbuminaemia

Permeability oedema

Question 29

Describe how treatment of breast cancer can lead to oedema

Answer 29

Radiotherapy to axilla to treat breast cancer can cause Lymphoedema

Radiotherapy ∴ fibrosis ∴ decreased lymph flow ∴ oedema of upper limb

Question 30

How would abnormal renal function cause oedema

Answer 30

Abnormal renal function ∴ retention of Na+ and H2O

Increased Na+ & H2O ∴ Increased intravascular fluid volume

This causes hydrostatic pressure in capillaries to go up ∴ more fluid out ∴ Peripheral oedema

Question 31

How would low protein levels cause oedema?

Answer 31

Hypoalbuminaemia means low oncotic pressure in the blood

Lower oncotic pressure ∴ higher filtration ∴ higher out flow into interstitium

Question 32

What would cause abnormal renal function?

Answer 32

Primary
- Acute tubular damage eg hypotension

Secondary
- Heart failure

Question 33

What would cause hypoalbumaemia?

Answer 33

Nephrotic syndrome

Hepatic cirrhosis

Malnutrition

Question 34

What would cause ‘permeability oedema’?

Answer 34

Burns or acute inflammation

Damage to endothelium creates ‘pores’ - meaning the permeability of the endothelium drops a lot

Means that proteins n shit can pass through

This means an EXUDATE goes out of the capillaries