Definition
Terms used to describe oedema
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Anasarca: Generalized subcutaneous oedema
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Ascites: Fluid in peritoneal cavity
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Hydrothorax; Edematous fluid in thorax
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Hydropericardium: Edematous fluid in pericardium
Oedema is of two types
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Inflammatory oedema
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Non-inflammatory odema
Mechanism of oedema formation
Two forces called “STARLING’S FORCES “
Physiology of fluid balance
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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.
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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
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Decreased plasma osmotic pressure
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Increased hydrostatic pressure
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Increased permeability of vascular endothelium
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Lymphatic obstruction
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Sodium retention
Decreased plasma osmotic pressure - Hypoproteinemia (Albuminemia)
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
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Malnutrition
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In advanced hepatic disease (Cirrhosis), protein synthesis will be affected leading to nutritional or cachetic oedema
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Loss of protein through intestine and stomach - stomach worms → Parasitic oedema
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Kidney or renal amyloidosis – blood lost in urine - Renal odema
Increased hydrostatic pressure
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.
Increased permeability of capillary endothelium
Lymphatic obstruction
Causes
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Tumours, cyst, abscess, bandages, thrombi
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Parasites (Demodex canis, mites)
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Filariasis – Wucheria bancrofti - humans
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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
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Congestive heart failure
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Nephrosis/Nephritis
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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.
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Characters
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Transudate
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Exudate
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1
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Colour
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Clear, water like pale yellow
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Cloudy, white, yellow-red
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2
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Consistency
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Thin, watery no tissue fragments
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Thick, creamy, contains tissue fragments
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3
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Odour
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None
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Have odour
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4
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Ph
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Alkaline
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Acidic
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5
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Specific gravity
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1.015 or less
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1.018 or higher
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6
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Protein
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Low, < 3%
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High > 4%
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7
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Cell count
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Low
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High, RBCs, WBCs
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8
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Enzyme count
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Low
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High
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9
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Bacteria
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None
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Present
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10
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Inflammation
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None
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Present
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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
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