Pathophysiology of Congestion and Oedema

Question 1

What does Darcy’s Law state?

Answer 1

Q = (change in) P/R, where Q = blood flow, P = pressure and R = resistance

Question 2

What is congestion?

Answer 2

A relative excess of blood in the vessels of a tissue or organ
Passive process
Secondary phenomenon

Question 3

What is the pathophysiology of a deep vein thrombosis of the leg?

Answer 3

Vein blocked causing localised acute congestion
Blood backs up in veins, venules and capillaries
Decreased outflow of blood
Local acute congestion
Decreased pressure gradient
Decreased flow across system
No oxygen, ischaemia and infarction

Question 4

What is the pathophysiology of hepatic cirrhosis?

Answer 4

Regenerative nodules of hepatocytes with intervening fibrosis which results from liver damage e.g. due to alcohol
Loss of normal architecture leading to altered hepatic blood flow
Portal blood flow blocked, congestion in portal vein and branches, increased portal venous pressure
Local chronic congestion
Haemorrhage risk

Question 5

What is the pathophysiology of congestive cardiac failure?

Answer 5

Heart unable to clear blood from left and right ventricles e.g. valve disease
Decreased cardiac output
Decreased renal glomerular filtration rate, activation of renin-angiotensin-aldosterone system increased Na and water retention
Increased amount of fluid in the body
Fluid overload in veins and back pressure
Central venous congestion in liver
Acute and chronic changes in the lungs

Question 6

What does central venous congestion in the liver lead to?

Answer 6

Right heart failure
Increased JVP
Hepatomegaly
Peripheral oedema

Question 7

What do acute and chronic changes in the lungs result in?

Answer 7

Pulmonary oedema
Left heart failure
Tachycardia
Crepitations in the lungs

Question 8

What is the pathophysiology of hepatic central venous congestion?

Answer 8

Stasis of poorly oxygenated blood in the hepatocytes

Question 9

What is an exudate?

Answer 9

A fluid with a high content of protein and cellular debris that has escaped from blood vessels and been deposited in tissues or on tissue surfaces

Question 10

What is a transudate?

Answer 10

An extravascular fluid with a low protein content and a low specific gravity (<1.012). It has low nucleated cell counts and the primary cell types are mononuclear cells e.g. macrophages, lymphocytes and mesothelial cells

Question 11

What are the features of the normal microcirculation?

Answer 11

Constant movement of fluid through the capillary beds
Driven by hydrostatic pressure from the heart
Balanced by osmotic pressures and endothelial permeability
Filtration from capillary beds to the interstitium

Question 12

What components of the circulation affect net flux and filtration?

Answer 12

Hydrostatic pressure
Oncotic pressure
Permeability characteristics and area of endothelium

Question 13

What does disturbance of the normal components of the microcirculation lead to?

Answer 13

Oedema

Question 14

What is oedema?

Answer 14

An accumulation of abnormal amounts of fluid in the extravascular space i.e. in inter-cellular tissue spaces and body cavities

Question 15

What are effusions?

Answer 15

Fluid collections in body cavities e.g. pleural, pericardial, joint effusions, ascites

Question 16

What are the features of transudate oedema?

Answer 16

Alterations in the haemodynamic forces which act across the capillary wall
Cardiac failure, fluid overload
Low protein/albumin
High water and electrolytes 
Low specific gravity

Question 17

What are the features of exudate oedema?

Answer 17

Part of the inflammatory process due to increased vascular permeability 
Tumour, inflammation or allergy 
High protein/albumin content
Water and electrolytes
High specific gravity

Question 18

How does left ventricular failure lead to pulmonary oedema?

Answer 18

Increased left atrial pressure, passive retrograde flow to the pulmonary veins, capillaries and arteries
Increased pulmonary vascular pressure
Increased pulmonary blood volume
Increased Pc leading to increased filtration and pulmonary oedema

Question 19

What happens in the lungs in pulmonary oedema?

Answer 19

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

Question 20

What is the pathophysiology of peripheral oedema?

Answer 20

Right heart failure, cannot empty the right ventricle in systole
Blood retained in the systemic veins leading to increased pressure in the capillaries, increased filtration and peripheral oedema
Also causes secondary portal venous congestion via the liver

In congestive cardiac failure, pulmonary oedema and peripheral oedema occur at the same time

Question 21

What is the pathophysiology of lymphatic blockage?

Answer 21

Lymphatic obstruction due to hydrostatic pressure upset
Lymphatic drainage is required for normal flow
If lymphatic system is blocked, lymphoedema occurs

Question 22

What is the pathophysiology of oedema in abnormal renal function?

Answer 22

Abnormal renal function results in salt and water retention
Secondary in heart failure due to reduced renal blood flow
Primary in acute tubular damage e.g. hypotension
Decreased renal function
Increased salt and water, increased intravascular fluid volume, secondary increase in Pc - all result in oedema

Question 23

What is the pathophysiology of low protein oedema?

Answer 23

In order to maintain endothelial permeability to water, normal protein levels are required
Hypoalbuminaemia results in decreased ability to maintain endothelial permeability and increased filtration

Question 24

What is the pathophysiology of permeability oedema?

Answer 24

Endothelial permeability – exudate

Damage to endothelial lining leads to increased pores in the membrane Proteins and larger molecules can leak out