Pathophysiology of Congestion and Oedema

Question 1

What is Darcy’s Law?

Answer 1

Q = Change in P/ R
Q is blood flow
P is pressure gradient on each side of membrane
R is resistance

Question 2

What is congestion?

Answer 2

Relative excess of blood in vessels of tissues or organ - vessels become distended or dilated
Is a passive process and is a secondary phenomenon
Can be acute or chronic

Question 3

What are some clinical pathology examples of congestion?

Answer 3

Local acute - DVT
Local chronic - hepatic cirrhosis
Generalised acute - congestive cardiac failure

Question 4

What happens in deep vein thrombosis to cause localised acute congestion?

Answer 4

Blood backs up in the veins, venules and capillaries so decreased outflow of blood causing acute congestion
Decrease in pressure gradient and flow across system so no O2 which can lead to ischaemia/infarction

Question 5

What does hepatic cirrhosis result form?

Answer 5

Severe liver damage - HBV or alcohol

Question 6

What happens to the damaged liver in hepatic cirrhosis?

Answer 6

Regenerating liver forms nodules of hepatocytes with intervening fibrosis
Loss of normal architecture so altered hepatic blood flow

Question 7

What does blockage of the portal blood flow lead to?

Answer 7

Congestion in portal vein and branches so increases portal venous pressure
Collateral circulation (dilates as increased pressure) - several sites anastomose with systemic circulation
Get local chronic congestion

Question 8

What is the risk of local chronic congestion?

Answer 8

Haemorrhage risk

Question 9

What are some consequences of local chronic congestion (hepatic cirrhosis)?

Answer 9

Portal-systemic shunts
Oesophageal Varices - fracture easily and can cause blood loss
Caput medusae - dilated veins show anastomose

Question 10

Explain congestive cardiac failure

Answer 10

Right and left chamber failure - effects in systemic and pulmonary system
Heart is unable to clear blood in both ventricles - ineffective pump - ischaemia and valve disease

Question 11

What is the pathophysiology of congestive cardiac failure?

Answer 11

Decreased CO as heart not pumping out blood
Reduced renal glomerular filtration rate (GFR) - activation of RAAS cause kidneys think they need more fluid
This increases Na and H2O retention so fluid is increased in body and in veins

Question 12

What is the treatment for congestive cardiac failure?

Answer 12

Diuretics

Question 13

What are the effects of congestive cardiac failure on the lungs?

Answer 13

Pulmonary oedema due left ventricular failure as blood dams back to lungs
Clinically get creps in the lungs and tachycardia

Question 14

What are the effects of congestive cardiac failure on the liver?

Answer 14

Central venous congestion
Due to right heart failure so blood dams back to systemic circulation
This causes a raised JVP, Hepatomegaly and peripheral oedema

Question 15

Describe hepatic central venous congestion

Answer 15

Nutmeg liver which is red/brown and pale
Spotty appearance macroscopically
Pericentral hepatocytes (red) show stasis of poorly oxygenated blood
Peripheral hepatocytes (pale) are better oxygenated as proximity to hepatic arterioles

Question 16

Describe the normal microcirculation

Answer 16

Constant movement of fluid through capillary beds - process of dynamic equilibrium
Driven by hydrostatic pressure of the heart and balanced by osmotic pressures and endothelial permeability

Question 17

Explain filtration on arterial and venous side in terms of oncotic and hydrostatic pressure?

Answer 17

Arterial side there is more fluid out as higher hydrostatic pressure inside artery
Venous side has more absorption due to higher oncotic pressure in the veins and venules

Question 18

What are the 3 components which affect the net flux and filtration?

Answer 18

Hydrostatic pressure
Oncotic pressure
Permeability characteristics and area of endothelium

Question 19

What does starling’s hypothesis and equation show?

Answer 19

Shows what net filtration is equal to
Disturbances of normal components causes oedema

Question 20

What is oedema?

Answer 20

Accumulation of abnormal amounts of fluid in the extravascular compartment - in intracellular tissue compartment and body cavities

Question 21

What is the difference in peripheral oedema and effusions?

Answer 21

Peripheral oedema is increased interstitial fluid in tissues
Effusions are fluid collections in body cavities

Question 22

What cause an oedema by transudate?

Answer 22

Alterations in the haemodynamic forces which act across the capillary wall
Can be due to cardiac failure and fluid overload

Question 23

Describe a transudate

Answer 23

Not much protein/ albumin but has lots of H2O and electrolytes
Low specific gradient

Question 24

What can cause an oedema by a exudate?

Answer 24

Change in vascular permeability
Part of inflammatory process and can be caused by tumour or allergy

Question 25

Describe an exudate

Answer 25

Higher protein/ albumin content H2O and electrolytes are lower than transudate High specific gradient

Question 26

What does peripheral oedema look like on a X-ray?

Answer 26

Fluffy in edges and centre Heart shadow increases Costomarginal angles disappear

Question 27

Describe the pathophysiology of pulmonary oedema?

Answer 27

Hydrostatic pressure - transudate Left ventricular failure so increases left atrial pressure and causes passive retrograde flow to pulmonary veins, capillaries and veins So increases pulmonary vascular pressure and blood volumes so causes filtration and oedema

Question 28

How can the lungs cause pulmonary oedema?

Answer 28

Perivascular and interstitial transudate Progressive oedematous widening of the alveolar septa and accumulation oedema fluid in the alveolar spaces

Question 29

Describe the pathophysiology of peripheral oedema?

Answer 29

Right heart failure so cant empty RV in systole so blood retained in systemic veins This increases Pressure so causes increase in filtration so peripheral oedema Also secondary portal venous congestion via liver

Question 30

What does cardiac failure lead to?

Answer 30

Is when right and left ventricles both fail Pulmonary oedema and peripheral oedema at same times All about the hydrostatic pressure

Question 31

What happens when the lymphatic system is blocked?

Answer 31

Lymphoedema

Question 32

What is lymphatic obstruction due to?

Answer 32

Hydrostatic pressure upset Can be caused by chemo ex. breast cancer which leads to fibrosis then increases outflow then oedema of upper limb

Question 33

Describe the pathophysiology of oedema in abnormal renal function

Answer 33

Decreased renal function which causes salt and water retention so increases intravascular fluid volume This causes a secondary increase in hydrostatic pressure which leads to oedema

Question 34

Describe the pathophysiology of low protein oedema

Answer 34

Due to oncotic pressure - transudate Oncotic pressure requires normal protein levels so hyperalbuminemia can cause decrease in oncotic pressure so increased filtration - oedema

Question 35

Describe the pathophysiology of permeability oedema

Answer 35

Endothelial permeability - exudate Damage to endothelial lining so increase in pores of membranes Osmotic coefficient decreases towards zero so proteins and larger molecules can leak out