• Clinical science



Edema is an abnormal accumulation of interstitial fluid caused by a variety of conditions, including, for instance, generalized fluid retention and localized reactions to trauma and allergies. Edema may manifest with swelling of the extremities (peripheral edema) or with internal fluid accumulation in organs and body cavities (e.g., pulmonary edema, pleural effusion). Patients with peripheral edema usually present with painless swelling of the lower legs. A residual indentation left by pressure on the site of the swelling indicates pitting edema. Bilateral lower limb pitting edema is often a sign of cardiac failure, while generalized peripheral pitting edema with swelling of the eyelids indicates hypoalbuminemia (e.g., in nephrotic syndrome). Nonpitting edema is seen especially in patients with lymphatic disorders and thyroid conditions.

General features

  • Definition: abnormal fluid accumulation in the interstitium due to an imbalance in fluid homeostasis
  • Types



Capillary fluid exchange

  • Definitions
    • Hydrostatic pressure
      • The pressure of any fluid enclosed in a space; (e.g., the force exerted by the blood confined within capillaries = capillary hydrostatic pressure)
      • Drives fluid out of capillaries into the interstitium
    • Osmotic pressure
      • Determined by concentration gradients: lower concentration solute is drawn across a semipermeable membrane into a higher concentration solute
      • Opposes hydrostatic pressure
      • Oncotic pressure (colloid osmotic pressure)
        • Osmotic force exerted by plasma proteins (mainly albumin)
        • Drives fluid from the interstitium into the capillaries and helps keeping intravascular fluid within blood vessels.
  • Starling forces: a model for determining movement of fluid between the capillary lumen and interstitium. For information on the Starling equation for the glomerulus see measurement of renal function in physiology of the kidney.
    • Jv = Kf [(Pc - Pi) - σ(πc - πi)]
      • Jv net fluid flow (positive values mean net fluid movement out of the capillary)
      • Kf coefficient for vessel permeability to fluid
      • Pc capillary hydrostatic pressure (drives fluid out of the capillary = filtration)
      • Pi interstitial hydrostatic pressure (attenuates filtration or even drives fluid into capillaries)
      • σ – Staverman reflection coefficient for permeability of vessel to protein
      • πc plasma colloid oncotic pressure (drives fluid into the capillary)
      • πi interstitial fluid colloid oncotic pressure (drives fluid out of capillary)
    • Net filtration
      • Depends on the hydrostatic pressure gradient (Pc - Pi) and the oncotic pressure gradient (πc - πi)
      • Filtration of fluid out of the capillary usually occurs on the arterial side of the capillary bed, mostly because of pressure from the arterial circulation (↑ Pc) and high plasma fluid levels (↓ πc).
      • Filtration of fluid into the capillary usually occurs on the venous side of the capillary bed, mostly because of capillary flow resistance (↓ Pc) and higher relative plasma protein levels following water filtration into the interstitium (↑ πc).
      • Outward filtration volume (arterial side) = inward filtration volume (venous side) + 10%
        • 10% of the filtered fluid is returned via lympathics rather than by blood vessels.

Pitting edema

  1. Fluid retention
  2. Protein deficiency; (mainly hypoalbuminemia : nephrotic syndrome, liver cirrhosis, malnutrition, protein-losing enteropathy
  3. Hydrostatic: chronic venous insufficiency; , pregnancy, deep vein thrombosis, post-thrombotic syndrome
  4. Increased capillary permeability: inflammation, burns, allergic reactions, trauma

Nonpitting edema

  • Lymphedema: : due to lymphatic obstruction (see below)
  • Myxedema: hypothyreosis; (generalized), hyperthyreosis (typically pretibial)

Generalized vs. localized edema

Generalized Localized



  • Chronic cardiac insufficiency
  • Chronic renal insufficiency
  • Liver cirrhosis
  • Malnutrition



  • Definition: edema associated with lymphatic obstruction and reduced fluid clearance due to compromised lymphatic vessels or lymph nodes
    • Lipid-rich, protein-rich fluid in the interstitial space that has high viscosity
  • Etiology
  • Clinical findings
    • Swelling of limbs; characteristically nonpitting edema
    • Swelling of toes and feet with deep flexion creases
    • Stemmer's sign: inability to lift a skin fold on the base of the second toe
  • Stages
    • Latent stage
    • Reversible swelling
    • Gradual fibrosis
    • Irreversible elephantiasis
  • Treatment
    • Conservative
      • Manual compression therapy and compression garments
      • Elevation of the involved limb
      • Exercise
      • Management of underlying disease
    • Surgical
      • Resection of lymphatic vessels
      • Lymphaticovenous anastomosis and lymphatic vessel grafting
      • Vascularized lymph node transfer