Pathophysiology of Congestion and Oedema Flashcards
What is meant by congestion?
•Relative excess of blood in vessels of a tissue or organ
Describe the nature of congestion (active or passive)?
Passive, acute inflammation is acive
What are clinical examples of congestion?
•Local acute congestion
–Deep vein thrombosis
•Local chronic congestion
–Hepatic cirrhosis
•Generalised acute congestion
–Congestive cardiac failure
Why does DVT in the leg cause congestion?
- 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
What does hepatic cirrhosis result from?
•Serious liver damage eg HBV, alcohol
How does hepatic cirrhosis result in local chronic congestion?
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:
- Congestion in portal vein branches
- Increased portal venous pressure
- Collateral circulation - several sites anastomose with systemic circulation
Local chronic congestion - haemorrhagic risk.
What is the risk of local chronic congestion?
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.)
What is the root cause of congestive heart failure?
•Heart unable to clear blood, right & left ventricles
Caused by ineffective pump eg ischaemia, valve disease
How does congestive heart failure result in an increase in the overall amount of fluid in the body
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)
What are the effects of congestive cardiac failure?
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
What is the oxygen supply of pericentral and periportal hepatocytes like?
Pericentral - stasis of poorly oxygenated blood. Red in colour
Periportal - Better oxygenated due to proximity of hepatic arterioles
What balances the hysrostatic pressure from the heart in the microcirculation?
Osmotic pressures and endothelial permeability
Where does filtration from capillary beds go?
To the interstitium
What is Oedema defined as?
Accumulatiuon of abnormal amounts of fluid in the extravascular compartment
–intercellular tissue compartment (extracellular fluid)
–body cavities
What is meant by peripheral oedema?
Increasedinterstitial fluid in the tissues
What are effusions?
Fluid collections in the body cavities.
- Pleural, pericardial, joint effusions
Abdominal cavity - ascites
What is the aetiology of transudates?
•Alterations in the haemodynamic forces which act across the capillary wall
•Cardiac failure, fluid overload
Describe the components of transudates
Lots of H2O and electrolytes
Not much protein/albumin
Low specific gravity
What is the aetiology of exudate?
Part of the inflammatory process due to increase in the vascular permeability
Tumour, inflammation, allergy
Describe the components of exudates
Higher protein/albumin content
H2O and Electrolytes
High specific gravity
How does left ventricular failure result in pulmonary oedema (transudate)?
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
What happens to the alveoli when there is pulmonary oedema? Caused by perivascular interstitial transudate
Progressive oedematous widening of the alveolar septa
Accumulation of oedema fluid in the alveolar spaces
What is the aetiology of peripheral oedema?
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
What is congestive heart failure?
RIght and left heart failure at the same time
Pulmonary oedema and peripheral odema at the same time
What causes lymphoedema?
Blockage of the lymphatic system, can stem from radiotherapy where potential damage to the lymph may occur, specifically breast cancer
How does abnormal renal function result in oedema?
- 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
What are the causes of low protein oedema?
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
How does permeability oedema arise?
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
