Edema and Shock

Edema

• Edema is an increased fluid in the interstitial tissue spaces
• Normal fluid homeostasis is maintained by vessel wall integrity, intravascular pressure, and osmolarity within certain physiologic ranges
• Causes of edema:
  • Increased hydrostatic pressure (e.g. heart failure, venous obstruction)
  • Decreased oncotic (osmotic) pressure (e.g. decreased albumin due to liver failure, malnutrition, or nephrotic syndrome)
  • Lymphatic obstruction
  • Sodium retention
  • Inflammation

Hyperemia and Congestion

• Hyperemia refers to an active process of increased blood volume within a tissue, resulting from arteriolar dilation and increased blood flow
• Congestion refers to a passive process of increased blood volume within a tissue, resulting from impaired outflow of venous blood
• Examples of hyperemia: physiologic (e.g. skeletal muscle during exercise), pathologic (e.g. acute inflammation)
• Examples of congestion: venous obstruction (e.g. ovarian torsion), cardiac failure

Liver Congestion

• Gross examination: areas of red-brown and slightly depressed tissue (nutmeg liver)
• Microscopic examination: centrilobular congestion with hepatocyte necrosis

Hemorrhage

• Hemorrhage is the extravasation of blood from vessels, often due to damage to blood vessels or defective clot formation
• Causes of hemorrhage: problems in blood vessels, platelets, or coagulation factors
• Types of hemorrhage:
  • External
  • Internal: hematoma, petechiae (1-2 mm), purpura (3-5 mm), ecchymoses (bruises, 1-2 cm)
• Clinical significance: depends on volume, rate, and site of hemorrhage, can lead to iron deficiency anemia, hypovolemic shock, and death

Shock

• Shock is a state of diminished cardiac output or reduced effective circulating blood volume, leading to tissue perfusion and cellular hypoxia
• Types of shock:
  • Hypovolemic shock
  • Cardiogenic shock
  • Anaphylactic shock (systemic vasodilation and increased vascular permeability due to immunoglobulin E-mediated hypersensitivity reaction)
  • Neurogenic shock (loss of vascular tone associated with anesthesia or spinal cord injury)
• Stages of shock:
  • Non-progressive stage: vital organ perfusion is maintained
  • Progressive stage: tissue hypoperfusion, worsening circulatory and metabolic derangement, and acidosis
  • Irreversible stage: cellular and tissue injury is severe, and survival is not possible even if hemodynamic defects are corrected

Learn about edema, its causes, and its relation to shock. Understand the normal fluid homeostasis and the factors that affect it.