What is edema. Causes and treatment of edema

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Edema

Definition

Edema is an abnormal accumulation of interstitial fluid within tissues. About 60% of lean body weight is water; two-thirds is intracellular and most of the remainder is interstitial fluid. When interstitial fluid accumulates beyond normal, edema results.

Fluid can also collect in body cavities:

Hydrothorax - pleural cavity
Hydropericardium - pericardial cavity
Hydroperitoneum (ascites) - peritoneal cavity
Anasarca - severe generalized edema with profound subcutaneous swelling and fluid in body cavities
Robbins & Kumar Basic Pathology, p. 78-79

Pathophysiology

Fluid movement across capillary walls is governed by two opposing forces:

Factors influencing fluid movement across capillary walls - Robbins Pathology

Vascular hydrostatic pressure - pushes fluid OUT of capillaries into the interstitium
Plasma colloid osmotic (oncotic) pressure - pulls fluid BACK into capillaries

Normally these are balanced, and the small net outflow into the interstitium is drained by lymphatics back to the circulation. Edema occurs when:

Hydrostatic pressure increases, OR
Colloid osmotic pressure decreases, OR
Lymphatic drainage is blocked, OR
Vascular permeability increases (inflammation)

Transudate (protein-poor fluid) = high hydrostatic or low oncotic pressure Exudate (protein-rich fluid) = increased vascular permeability (inflammation)

Causes of Edema

Here is a summary diagram of peripheral edema causes:

Peripheral edema - causes by mechanism (Frameworks for Internal Medicine)

1. Increased Hydrostatic Pressure

Caused mainly by disorders that impair venous return:

Cause	Mechanism
Congestive heart failure	Reduced cardiac output → venous pooling + renal sodium/water retention via RAAS
Deep vein thrombosis (DVT)	Local venous obstruction → unilateral leg edema
Renal failure	Sodium and water retention → increased intravascular volume
Liver cirrhosis	Portal hypertension → ascites and lower limb edema
Constrictive pericarditis	Impaired cardiac filling → elevated venous pressure
Venous insufficiency	Incompetent valves → chronic venous hypertension
Superior vena cava (SVC) syndrome	Obstruction of the SVC → face, neck, upper limb edema
Pregnancy	Inferior vena cava compression by gravid uterus
Prolonged limb dependency / inactivity	Reduced venous pump

In congestive heart failure, a vicious cycle develops: reduced cardiac output → renal hypoperfusion → RAAS activation → Na+/water retention → increased venous pressure → worsening edema. This responds to salt restriction, diuretics, and aldosterone antagonists. - Robbins & Kumar Basic Pathology, p. 80

2. Reduced Plasma Osmotic (Oncotic) Pressure

Caused by hypoalbuminemia (plasma albumin < 2 g/dL is associated with edema):

Cause	Mechanism
Nephrotic syndrome	Glomerular damage → albumin lost in urine
Liver disease (cirrhosis)	Decreased albumin synthesis
Malnutrition / kwashiorkor	Inadequate protein intake
Protein-losing enteropathy	GI losses of protein

Low albumin leads to edema, reduced intravascular volume, renal hypoperfusion, and secondary hyperaldosteronism - which worsens edema because the primary defect (low protein) persists. - Robbins & Kumar Basic Pathology, p. 80

3. Lymphatic Obstruction (Lymphedema)

Impaired lymphatic drainage prevents resorption of interstitial fluid:

Cause	Example
Parasitic infection	Filariasis - causes elephantiasis (massive lower limb edema)
Malignancy	Lymphoma obstructing lymphatics; breast cancer causing peau d'orange
Post-surgical / irradiation	Axillary node dissection in breast cancer → arm lymphedema
Iatrogenic	Radiation treatment disrupting lymphatics

Robbins & Kumar Basic Pathology, p. 80

4. Increased Vascular Permeability (Inflammatory Edema)

In inflammation, mediators such as histamine, bradykinin, leukotrienes, and cytokines increase capillary permeability, allowing protein-rich fluid to leak out. This produces an exudate. Examples:

Allergic reactions / anaphylaxis
Burns
Sepsis / ARDS
Infections

5. Sodium and Water Retention

Excessive salt retention increases hydrostatic pressure and dilutes plasma proteins:

Renal failure
Primary hyperaldosteronism
Drugs (corticosteroids, NSAIDs, some antihypertensives)

6. Medications (Iatrogenic Edema)

Common culprits include:

Calcium channel blockers (amlodipine)
NSAIDs
Corticosteroids
Thiazolidinediones (e.g., pioglitazone)
Hormonal therapy (estrogens)

Clinical Features

Type	Characteristics
Heart failure	Bilateral, symmetric, dependent, pitting; gradual onset; legs primarily; may have ascites/pleural effusions
Renal failure	Similar to right heart failure; generalized
Cirrhosis	Bilateral, pitting, dependent; mainly lower limbs; ascites prominent
DVT	Unilateral, dependent, pitting; acute onset; associated with pain and erythema
SVC syndrome	Face, neck, bilateral arms
Lymphedema	Non-pitting (in chronic stage); involves limb; may be unilateral
Nephrotic syndrome	Periorbital edema (morning), then generalized; associated with proteinuria

Frameworks for Internal Medicine, p. 308-309

Treatment of Edema

Treatment is directed at the underlying cause plus symptomatic fluid removal:

1. Treat the Underlying Cause

Heart failure: ACE inhibitors, ARBs, beta-blockers, cardiac resynchronization
Renal failure: Hemodialysis or peritoneal dialysis to maintain fluid balance
Nephrotic syndrome: Treat underlying glomerular disease; RAAS blockade; corticosteroids (where indicated)
Cirrhosis: Treat liver disease; reduce portal hypertension
DVT: Anticoagulation (heparin, then warfarin or DOACs)
SVC syndrome: Treat underlying malignancy (chemotherapy, radiation, stenting)
Lymphedema: Treat underlying infection or malignancy

2. Dietary Sodium and Fluid Restriction

Sodium restriction is a cornerstone of edema management in heart failure, cirrhosis, and renal failure
Diuretics work better when combined with low-sodium diet

3. Diuretics

The most widely used pharmacological treatment:

Diuretic Class	Examples	Used in
Loop diuretics	Furosemide, bumetanide	Heart failure, renal failure, pulmonary edema
Thiazide diuretics	Hydrochlorothiazide	Mild edema, hypertension-related
Aldosterone antagonists	Spironolactone, eplerenone	Heart failure, cirrhosis (reduces secondary hyperaldosteronism)
Osmotic diuretics	Mannitol	Cerebral edema

Note: In severe heart failure, bowel wall edema can impair oral diuretic absorption - parenteral (IV) administration is required. - Frameworks for Internal Medicine, p. 308

4. Mechanical / Physical Measures

Leg elevation - reduces dependent edema by promoting venous return
Compression stockings - chronic venous insufficiency, DVT prevention, lymphedema
Compression bandaging - lymphedema management
Manual lymphatic drainage - physiotherapy for lymphedema

5. Dialysis / Ultrafiltration

For renal failure with hypervolemia: hemodialysis or peritoneal dialysis
Plasma ultrafiltration can remove several liters per day in severe pulmonary edema
Frameworks for Internal Medicine, p. 308

6. Albumin Infusion

Used in hypoalbuminemia (nephrotic syndrome, cirrhosis) to temporarily restore oncotic pressure
Combined with diuretics for best effect in cirrhotic ascites

7. Specific Interventions

Paracentesis - large-volume drainage of ascites in cirrhosis
Thoracentesis - drainage of large pleural effusions (hydrothorax)
Surgical/endovascular - venous stenting in SVC syndrome; lymphovenous anastomosis in lymphedema

Summary Table

Mechanism	Key Causes	Treatment Focus
↑ Hydrostatic pressure	Heart failure, DVT, renal failure, cirrhosis	Diuretics, Na restriction, treat primary disease
↓ Oncotic pressure	Nephrotic syndrome, cirrhosis, malnutrition	Treat underlying disease, albumin, diuretics
Lymphatic obstruction	Filariasis, malignancy, post-surgical	Compression, physiotherapy, treat cause
↑ Vascular permeability	Inflammation, burns, sepsis, allergy	Anti-inflammatory, treat infection, manage ARDS
Na/H2O retention	Renal failure, aldosteronism, drugs	Dietary restriction, diuretics, dialysis

Sources:

Robbins & Kumar Basic Pathology (Robbins Pathology), pp. 78-80
Frameworks for Internal Medicine, pp. 307-310
Goldman-Cecil Medicine International Edition
Harrison's Principles of Internal Medicine 22E

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