Pathophysiology of Congestion and Oedema

Question 1

What is meant by congestion?

Answer 1

•Relative excess of blood in vessels of a tissue or organ

Question 2

Describe the nature of congestion (active or passive)?

Answer 2

Passive, acute inflammation is acive

Question 3

What are clinical examples of congestion?

Answer 3

•Local acute congestion

–Deep vein thrombosis

•Local chronic congestion

–Hepatic cirrhosis

•Generalised acute congestion

–Congestive cardiac failure

Question 4

Why does DVT in the leg cause congestion?

Answer 4

• Blood backs up in veins, venules, capillaries
• Reduced outflow of blood
• local, acute congestion
• Reduced pressure gradient
• Reduced flow across system (by Darcy’s law)
• No O2 - ischaemia and infarction

Question 5

What does hepatic cirrhosis result from?

Answer 5

•Serious liver damage eg HBV, alcohol

Question 6

How does hepatic cirrhosis result in local chronic congestion?

Answer 6

Regenerating liver forms nodules of hepatocytes surrounded by fibrous tissue (fibrosis)

Loss of normal architecture (inherrent loss of function) - altered hepatic blood flow

Portal blood flow blocked:

1. Congestion in portal vein branches
2. Increased portal venous pressure
3. Collateral circulation - several sites anastomose with systemic circulation

Local chronic congestion - haemorrhagic risk.

Question 7

What is the risk of local chronic congestion?

Answer 7

Haemorrhagic risk

Portal - systemic shunts (shunt between the portal vein which carries blood from the intestines to the liver and the hepatic vein which carries blood from the liver back to the heart.)

Question 8

What is the root cause of congestive heart failure?

Answer 8

•Heart unable to clear blood, right & left ventricles

Caused by ineffective pump eg ischaemia, valve disease

Question 9

How does congestive heart failure result in an increase in the overall amount of fluid in the body

Answer 9

Reduced cardiac output

Reduced GFR

• activating •renin-angiotensin-aldosterone system (perhaps by renal baroreceptors or reduced sodium concentration detected by macula densa)
• Incrase in sodium and H2O retention

Increasing the amount of fouid in the body

•Fluid (overload) in veins (Treatment: diuretics)

Question 10

What are the effects of congestive cardiac failure?

Answer 10

Back pressure - blood dammed back in the veins

•Lungs - pulmonary oedema

–Left heart failure – blood dams back into lungs

–Clinically, crepitations in lungs, tachycardia

•Liver - central venous congestion

–Right heart failure- blood dams back to systemic circulation

–­ JVP, hepatomegaly, peripheral oedema

Question 11

What is the oxygen supply of pericentral and periportal hepatocytes like?

Answer 11

Pericentral - stasis of poorly oxygenated blood. Red in colour

Periportal - Better oxygenated due to proximity of hepatic arterioles

Question 12

What balances the hysrostatic pressure from the heart in the microcirculation?

Answer 12

Osmotic pressures and endothelial permeability

Question 13

Where does filtration from capillary beds go?

Answer 13

To the interstitium

Question 14

What is Oedema defined as?

Answer 14

Accumulatiuon of abnormal amounts of fluid in the extravascular compartment

–intercellular tissue compartment (extracellular fluid)

–body cavities

Question 15

What is meant by peripheral oedema?

Answer 15

Increasedinterstitial fluid in the tissues

Question 16

What are effusions?

Answer 16

Fluid collections in the body cavities.

• Pleural, pericardial, joint effusions

Abdominal cavity - ascites

Question 17

What is the aetiology of transudates?

Answer 17

•Alterations in the haemodynamic forces which act across the capillary wall

•Cardiac failure, fluid overload

Question 18

Describe the components of transudates

Answer 18

Lots of H2O and electrolytes

Not much protein/albumin

Low specific gravity

Question 19

What is the aetiology of exudate?

Answer 19

Part of the inflammatory process due to increase in the vascular permeability

Tumour, inflammation, allergy

Question 20

Describe the components of exudates

Answer 20

Higher protein/albumin content

H2O and Electrolytes

High specific gravity

Question 21

How does left ventricular failure result in pulmonary oedema (transudate)?

Answer 21

There is a resultant increase in left atrial pressure - passive retrograde flow to the pulmonary veins, capillaries and arteries

Increase pulmonary vasculature pressure

Increase in pulmonary blood volume

Increase in filtration and pulmonary oedema

Question 22

What happens to the alveoli when there is pulmonary oedema? Caused by perivascular interstitial transudate

Answer 22

Progressive oedematous widening of the alveolar septa

Accumulation of oedema fluid in the alveolar spaces

Question 23

What is the aetiology of peripheral oedema?

Answer 23

Right heart failure - cannot empty right side in systole

Blood retained in systemic veins - increase in the pressure in capillaries - increase filtration and therefore peripheral oedema

Question 24

What is congestive heart failure?

Answer 24

RIght and left heart failure at the same time

Pulmonary oedema and peripheral odema at the same time

Question 25

What causes lymphoedema?

Answer 25

Blockage of the lymphatic system, can stem from radiotherapy where potential damage to the lymph may occur, specifically breast cancer

Question 26

How does abnormal renal function result in oedema?

Answer 26

• Abnormal renal function results in Salt (NaCl) and H2O retention
• Secondary in heart failure - reduced renal blood flow
• Primary: acute tubular damage eg hypotension (as a result of shock or blood loss)

Decrease in renal function is the result of both

Increase in salt and H2O

Increase in intravascular fluid volume

Resulting in oedema

Question 27

What are the causes of low protein oedema?

Answer 27

Nephrotic syndrome: leaky renal glomerular basement membrane; lose protein; generalised oedema

Hepatic cirrhosis: diffuse fibrosis in liver, liver unable to synthesis enough protein

Malnutrition - insufficient intake or protein

Question 28

How does permeability oedema arise?

Answer 28

Endothelal permeability increases so (excudate)

Damage to the endothelial lining resulting in pores in the membrane

Proteins and larger molecules can leak out

Results from acute inflammation such as pneumonia

Results from burns