Oedma

OEDEMA

Definition

  • Abnormal accumulation of fluid in the intercellular tissue spaces or body cavities
    • Localized : Due to obstruction of venous outflow – leg
    • Generalized : Chronic venous Congestion or heart failure

Terms used to describe oedema

  • Anasarca: Generalized subcutaneous oedema
  • Ascites: Fluid in peritoneal cavity
  • Hydrothorax; Edematous fluid in thorax
  • Hydropericardium: Edematous fluid in pericardium

Oedema is of two types

  1. Inflammatory oedema
  2. Non-inflammatory odema

Mechanism of oedema formation

Two forces called “STARLING’S FORCES “

  • Filtration force: Expels fluid from the vessel
  • Absorption force: Draws fluid into the vessel

Physiology of fluid balance

  • At the arterial end of capillary hydrostatic pressure is 45mm of Hg and osmotic pressure of blood is 30mm of Hg (due to albumin / globulin). Therefore, fluid expelled into the intercellular space (filtration force) is 15mm Hg.
  • At te venous end, hydrostatic pressure of blood falls to 15mm of Hg and osmotic pressure of blood is 30mm of Hg. Therefore, absorption force is 15mm of Hg

CAUSES OF OEDEMA

  • Decreased plasma osmotic pressure
  • Increased hydrostatic pressure
  • Increased permeability of vascular endothelium
  • Lymphatic obstruction
  • Sodium retention

Decreased plasma osmotic pressure - Hypoproteinemia (Albuminemia)

  • Decreased protein synthesis
  • Excessive loss from blood - Low osmotic pressure in the blood - More fluid flows into intercellular space

Hydrostatic pressure at arterial end is 45mm Hg and osmotic pressure at arterial end is 20mm Hg. So, the rate of fluid flow into tissues is 25mm Hg. Osmotic pressure at venous end is 20mm Hg and hydrostatic pressure is 15mm Hg. Thereby, the rate of fluid flow in to vein is 5mm Hg. Because of the pressure diffeences ( Hydrostatic and osmotic pressure) at the arterial and venous end, the rate of fluid accumulation in tissues is 20mm Hg

Decreased plasma osmotic pressure mostly results in generalised and severe oedema

  • Malnutrition
  • In advanced hepatic disease (Cirrhosis), protein synthesis will be affected leading to nutritional or cachetic oedema
  • Loss of protein through intestine and stomach - stomach worms → Parasitic oedema
  • Kidney or renal amyloidosis – blood lost in urine - Renal odema

Increased hydrostatic pressure

  • General or passive hyperaemia → venous stasis
  • Central lesion in heart or lungs or local obstruction in a vein

Hydrostatic pressure at arterial end is 45mm Hg, whereas osmotic pressure is 30mm Hg. So the rate of  fluid flow into tissues is 15mm Hg. At the venous end,  osmotic pressure is 30mm Hg and hydrostatic pressure is 25mm Hg.  The rate of fluid flow into vein is 10mm Hg. So the rate of fluid accumulating in tissues is 5mm Hg.

  • This type of oedema is mild. Mainly the cause is in the heart. Hence called cardiac oedema.

Increased permeability of capillary endothelium

  • Due to venous stasis → increased hydrostatic pressure

Lymphatic obstruction

Causes

  • Tumours, cyst, abscess, bandages, thrombi
  • Parasites (Demodex canis, mites)
  • Filariasis – Wucheria bancrofti - humans
  • Inflammatory conditions – farcy; ulcerative lymphangitis

In lymphatic obstruction, fluid and protein in intercellular space will not be drained leading to oedema (LYMPHOEDEMA)

Sodium retention

Causes

  • Congestive heart failure
  • Nephrosis/Nephritis
  • Acute renal failure

Due to failure of excretion sodium in urine, water will be retained leading to generalized oedema

Differences between transudate and exudate

S. No.

Characters

Transudate

Exudate

1

Colour

Clear, water like pale yellow

Cloudy, white, yellow-red

2

Consistency

Thin, watery no tissue fragments

Thick, creamy, contains tissue fragments

3

Odour

None

Have odour

4

Ph

Alkaline

Acidic

5

Specific gravity

1.015 or less

1.018 or higher

6

Protein

Low, < 3%

High > 4%

7

Cell count

Low

High, RBCs, WBCs

8

Enzyme count

Low

High

9

Bacteria

None

Present

10

Inflammation

None

Present

Macroscopical appearance 

  • Swollen, increase in weight
  • Cold due to decrease blood, flow and increase heat dissipation
  • Less color
  • No pain
  • Incision results in flow of fluid from cut surface
  • Pits on pressure
  • Fibrosis

Microscopical appearance 

  • Space between adjacent cells widened
  • During life space filled with fluid
  • H&E stain - fine granular material - stains faintly pink - ↑ pink if ↑ protein
  • Atrophy of parenchymatous cells
  • Fibrosis - chronic cases

Significance and result 

  • Disappears if cause is removed
  • Oedema in lung & brain are fatal
  • Subcutaneous oedema impairs wound healing
Last modified: Wednesday, 7 December 2011, 7:21 AM