Pathophysiology of congestion & oedema Flashcards
What is congestion?
Relative excess of blood in vessels of tissue or organ
Is congestion passive or active?
Passive
Is congestion acute or chronic?
Acute or chronic
Using the idea of Darcy’s law, what must happen in order for congestion to occur?
Blood flow = Pressure/resistance
Congestion (drop in blood outflow) will occur if the pressure gradient drops or resistance increases
Congestion is quite a wide term and covers many examples
Give some pathological examples of congestion, and what causes them
Local acute congestion:
- Deep vein thrombosis
Local chronic congestion:
- Hepatic cirrhosis
Generalised acute congestion:
- Congestive cardiac failure
What is local acute congestion?
Congestion due to something like DVT which blocks venous drainage
The main risks are ischaemia and infarction of the affected tissue
Hepatic cirrhosis is an example of something that causes local chronic congestion
What is hepatic cirrhosis?
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
Why does hepatic cirrhosis cause local chronic congestion?
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
What risk is associated with local chronic congestion?
Haemorrhage
portal venous pressure very high because portal flow is blocked
Hepatic cirrhosis causes local congestion in the portal vein and its branches
What happens to all this congested blood?
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
What is congestive heart failure?
Basically a build up of fluid in your body due to the heart being unable to effectively pump blood
Describe how congestive heart failure actually causes congestion
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
How is congestive heart failure treated?
Diuretics
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?
Left heart = receives blood from pulmonary circulation
LH failure ∴ blood dams back into lungs ∴ pulmonary oedema
How can left heart failure be identified on examination?
Palpation - tachycardia
Auscultation - crepitations in lungs
What are the effects of right heart failure?
Right heart = receives blood from systemic circulation
RH failure ∴ blood dams back into systemic circulation
Increased JVP
Hepatomegaly
Peripheral oedema
What clinical signs on examination, would indicate right heart failure?
Inspection - increased JVP & peripheral oedema
Palpation - peripheral oedema & Hepatomegaly
What risk does congestive heart failure pose to the liver?
Hepatic central venous congestion - ‘Nutmeg liver’
Describe/explain the appearance of nutmeg liver
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
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?
Hydrostatic pressure
Osmotic/oncotic pressures n all them
Aside from pressures, what affects the amount/rate of fluid moving between capillaries and the interstitium?
Permeability characteristics of vessels
Area of endothelium
What is oedema?
Accumulation of abnormal amounts of fluid in extravascular compartments
Extravascular Compartments can refer to intercellular tissue compartments (extracellular fluid) or to body cavities
Oedema can mean fluid collecting in a body cavity
What is the name specifically for this?
Effusion
Effusions: fluid collections in body cavities
Pleural, pericardial, joint effusions
Abdominal cavity - ascites
The fluid in oedema can either be exudates, or transudates
What are these?
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
What happens in pulmonary oedema?
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
Pulmonary oedema can eventually involve build up of transudate in the alveolar spaces
How does this occur?
Build up of perivascular & interstitial transudate
Progressive oedematous widening of alveolar septa
This allows transudate to accumulate in alveolar spaces
Which is involved in peripheral oedema, transudate or exudate?
Transudate
Give some examples of causes of oedema
Heart failure
Lymphatic blockage
Abnormal renal function
Hypoalbuminaemia
Permeability oedema
Describe how treatment of breast cancer can lead to oedema
Radiotherapy to axilla to treat breast cancer can cause Lymphoedema
Radiotherapy ∴ fibrosis ∴ decreased lymph flow ∴ oedema of upper limb
How would abnormal renal function cause oedema
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
How would low protein levels cause oedema?
Hypoalbuminaemia means low oncotic pressure in the blood
Lower oncotic pressure ∴ higher filtration ∴ higher out flow into interstitium
What would cause abnormal renal function?
Primary
- Acute tubular damage eg hypotension
Secondary
- Heart failure
What would cause hypoalbumaemia?
Nephrotic syndrome
Hepatic cirrhosis
Malnutrition
What would cause ‘permeability oedema’?
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
