Local Oedema

• Local oedema is the local accumulation of excess interstitial fluid.
• Caused by disturbance of the balance betwen fluid extravasation and resorption at the level of the capillaries.
  • Outwards Forces - arteriolar
    • Vasuclar hydrostatic pressure - 35 mmHg
    • Interstitial osmotic pressure - 3 mmHg
  • Inwards forces - venular
    • Plasma protein osmotic pressure - 25 mmHg
    • Interstitial hydrostatic pressure - 4 mmHg
• May be of inflammatory or non-inflammatory origin.

Types of Local Oedema

Inflammatory oedema

• Generated by one or more of the following:
  1. Increased vascular permeability
  2. Increased arteriolar blood pressure
  3. Breakdown of tissue protein or transfer of plasma proteins into ECF.
     • Results in raised osmotic pressure of tissue fluid.
  4. Obstruction to lymphatic drainage.
     • Usually by fibrin.

Lymphatic oedema

• Results in accumulation of high protein fluid.
• May provoke a granulation or fibrous tissue response.
• Due to:
  1. Lymphangitis/ lymphadenitis
     • Acute inflammation of lymphatics/ lymph nodes. R
     • Caused by stasis in lymphatics and/or bacterial infection.
     • E.g. “Monday Morning leg” in horses.
  2. Chronic inflammation caused by persistent or granuloma-producing bacterial infection.
     • E.g. Johne's disease, actinobacillosis.
  3. Tumour spread.
     • Metastasis of tumour cell plugs lymphatics and nodes
     • e.g. mammary carcinoma.
  4. Parasitic migration
     • Larvae may be following their normal pathway (e.g. Schistosomiasis), or may be aberrant.

Local venous obstruction

• Obstruction to venous drainage may be mechanical or inflammatory-mediated.
  • Causes raised hydrostatic pressure.
  • Endothelial permeability increases due to hypoxia.
  • There may be inflammatory damage.
• Mechanical obstruction, e.g.
  • Torsions of bowel
  • Misplaced organs.
  • Pressure from outside vein from adjacent structures.
    • Tumours.
• Venous inflammation (phlebitis)
  • May be associated with thrombosis (thrombophlebitis).

"Allergic" oedema

• Results from immediate (Type I ) or delayed (Type IV) hypersensitivity.
• Vasular permeability is increased due to release of histamine and vaso-dilating substances.
• E.g.
  • Insect stings (immmediate).
  • Vaccination (delayed).
  • Food reaction (delayed).