Pathogenic Classification of Edema

Edema Overview

• Abnormal accumulation of fluid in interstitial spaces and body cavities, resulting in conditions like hydrothorax, hydropericardium, and hydroperitoneum (ascites).

Types of Edema

• Anasarca: Severe generalized edema causing extensive subcutaneous swelling.
• Pitting Edema: Indentation remains after pressing the swollen area; associated with fluid excess due to increased venous hydrostatic pressure from conditions like heart failure and venous obstruction.
• Non-Pitting Edema: Fluid is bound in the interstitium; potential causes include myxedema from hypothyroidism and lymphatic system blockages.

Fluid Dynamics

• Fluid balance is maintained by the interplay of vascular hydrostatic pressure and plasma colloid osmotic pressure.
• Lymphatic system is responsible for draining excess interstitial fluid.

Edema Types and Characteristics

• Transudate: Non-inflammatory, protein-poor fluid with a specific gravity below 1.012; occurs from hydrodynamic shifts.
• Exudate: Inflammatory fluid with increased vascular permeability, typically with a specific gravity over 1.020.
• Movement of fluid is influenced by osmotic gradients, hydrostatic pressure, and oncotic pressure.

Pathophysiological Considerations

• Increased hydrostatic pressure at the arterial end leads to vasoconstriction and potential hypertrophy of vessel walls over time.

Brain and Pulmonary Edema

• Brain Edema: Caused by tumors, intoxication, or inflammation; can lead to fatal herniation and results from increased extracellular fluid due to vascular permeability and obstruction of cerebrospinal fluid flow.
• Cytotoxic Brain Edema: Increased intracellular fluid linked to ischemic or hypoxic injuries.
• Pulmonary Edema: Typically results from left-sided heart failure, characterized by foamy fluid affecting oxygenation.

Causes of Edema

• General causes include:
  • Increased capillary pressure
  • Decreased colloid osmotic pressure
  • Increased capillary permeability
  • Blocked lymphatic drainage
• Non-inflammatory edema causes include:
  • Increased hydrostatic pressure due to conditions like congestive heart failure
  • Reduced plasma osmolality from nephritic syndromes or liver cirrhosis
  • Sodium retention from excessive salt intake and renal insufficiency.

Specific Causes of Non-Inflammatory Edema

• Increased hydrostatic pressure may result from conditions such as constrictive pericarditis, venous obstruction, and prolonged inactivity.
• Reduced plasma osmotic pressure is commonly associated with nephrotic syndrome, liver cirrhosis, and severe malnutrition.
• Sodium retention can be triggered by renal hypoperfusion and prolonged excessive dietary intake.