Oedema

Introduction

Oedema is NOT a disease; it is the sign of a disease state.

• Oedema is defined as :"The swelling of tissues resulting from accumulation of excess fluid in the intercellular tissue spaces and serous cavities."

• Small amounts of fluid are normally present to lubricate cavities and viscera - this is not oedema.
• Excess fluid may accumulate in:
  • Subcutaneous tissue and between muscle.
  • Serous cavities.
    • Depending on the cavity, this has different terms.
      • Thorax - hydrothorax.
      • Pericardium - hydropericardium
      • Abdomen - hydroperitoneum (ascites).
    • Anasarca is when there is generalised body cavity accumulation plus subcutaneous involvement.
  • Lungs.

Composition of oedema fluid

• Inflammatory oedema which produces an exudate.
  • This is a protein rich fluid containing many inflammatory cells.
• Non inflammatory oedema which produces a transudate.
  • This fluid is low in protein and cells.
• Transudates and exudates are distinguished by the following criteria:

Criteria	Transudate	Exudate
Appearance	Clear/ pale yellow ("straw coloured")	Dark yellow, red or brown. Often cloudy or opaque.
Consistency	Thin, serous	Viscous
Protein content	0.05 - 0.5%, mainly albumin	Usually 2 - 4%
Coagulability	No fibrinogen, no coagulation	Contains fibrinogen, coagulates
Specific gravity	Low (< 1.012)	High (1.012 - 1.020) +
Cell content	Very low. mesothelial cells, some macropahges and lymphocytes/Monocytes.	High. Often macrophages, neutrophils, lymphocyes etc. Depends on cause and chronicity

• Examples of transudates:
  • Ascites
    • Excessive fluid in abdominal cavity.
  • Hydrothorax
    • Excessive fluid in the thorax.
  • Hydropericardium
    • Excessive fluid in the pericardium.
  • Anasarca
    • Generalised tissue oedema most noticeable in subcutaneous tissues.
  • Ventral subcutaneous oedema
• Seen in heart failure in horses and cattle.