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Edema

Chapter 43 | Part 2: Cardinal Manifestations and Presentation of Diseases · Part 2 – Cardinal Manifestations & Presentation · Chapter 43

Key Clinical Points

  1. Edema is defined as an excess of interstitial fluid that becomes clinically evident.
  2. Fluid movement to the interstitium is driven by capillary hydrostatic pressure and opposed by plasma colloid oncotic pressure.
  3. Reduced effective arterial volume (EAV) triggers a neurohumoral response (RAAS, SNS, AVP) leading to renal sodium and water retention.
  4. Natriuretic peptides (ANP, BNP) oppose sodium retention but are often insufficient in heart failure or cirrhosis due to increased resistance to their actions.
  5. Cyanosis can be caused by methemoglobin (Hb Fe3+) or sulfhemoglobin; clubbing is associated with lung disease, heart disease, or hepatic cirrhosis.
  6. Heart failure edema is typically dependent and worse in the evening; nephrotic syndrome edema is often periorbital and worse in the morning.
  7. Hepatic cirrhosis edema typically begins as ascites due to portal hypertension before peripheral edema develops.
  8. Lymphedema is particularly intractable due to increased intracapillary pressure and interstitial protein concentration.
  9. Refeeding edema occurs due to insulin release increasing tubular sodium reabsorption.
  10. Drug-induced edema can be caused by NSAIDs, calcium channel blockers, thiazolidinediones, and several others including cyclosporine and steroids.

1. DEFINITION & OVERVIEW

• Definition: Edema is an excess of interstitial fluid that has become evident clinically. • Fluid Dynamics: ◦ Constant exchange occurs between the intravascular and interstitial compartments of the extracellular fluid. ◦ Movement to interstitium: Driven by capillary hydrostatic pressure and opposed by colloid oncotic pressure in the interstitial fluid. ◦ Return to vasculature: Primarily via the lymphatic system. • Mechanisms of Edema Formation: A net movement of fluid from the intravascular to the interstitial spaces occurs under the following conditions: 1. \uparrow Intracapillary hydrostatic pressure 2. Inadequate lymphatic drainage 3. \downarrow Oncotic pressure of plasma 4. Damage to or dysfunction of the capillary endothelial barrier 5. \uparrow Oncotic pressure of the interstitial space

• Cyanosis and Clubbing: ◦ Cyanosis: Can be caused by small quantities of circulating methemoglobin (Hb Fe3+) and even smaller quantities of sulfhemoglobin or magnetic resonance imaging (MRI). These conditions impair oxygen delivery to tissues. ◦ Clubbing: Selection bulbous enlargement of the distal segments of the fingers and toes due to proliferation of connective tissue, particularly on the dorsal surface. There is also increased sponginess of the soft tissue at the base of the clubbed nail. ◦ Clinical Note: Clubbing does not occur with abnormal hemoglobin species (methemoglobin or sulfhemoglobin). ◦ Hypertrophic Osteoarthropathy: Associated with lung cancer, mesothelioma, bronchiectasis, or hepatic cirrhosis; characterized by subperiosteal formation of new bone in the distal diaphyses of long bones, causing pain and symmetric arthritis-like changes.

2. EPIDEMIOLOGY

• Peripheral Cyanosis: The most common cause is normal vasoconstriction resulting from exposure to cold air or water. ◦ Mechanism: Reduced cardiac output → cutaneous vasoconstriction → blood diverted from skin to CNS and heart. ◦ Note: Cyanosis of the extremities may occur even when arterial blood is normally saturated.

3. ETIOLOGY & PATHOPHYYSICS

• Reduction of Effective Arterial Volume (EAV): ◦ Definition: A parameter representing the filling of the arterial tree and the extent to which it effectively perfuses tissues. ◦ Causes of Underfilling: 1. \downarrow Cardiac output and/or \downarrow systemic vascular resistance 2. Pooling of blood in the splanchnic veins (e.g., cirrhosis) 3. Hypoalbuminemia

• Renal Response to Underfilling: ◦ Diminished renal blood flow is translated by the renal efferent arterioles. ◦ Resulting Actions: \downarrow Hydrostatic pressure in peritubular capillaries, \uparrow capillary permeability, and \uparrow colloid osmotic pressure in these vessels. ◦ Outcome: Enhanced salt and water reabsorption in the proximal tubule and ascending limb of the loop of Henle.

• Neurohumoral Activation: ◦ RAAS: Activation causes sodium and water retention. → Blockade of Angiotensin II (Ang II) or its receptors enhances sodium/water excretion. → Aldosterone: Stimulated by Ang II; enhances sodium reabsorption and potassium excretion in the collecting tubule. → Blockade of aldosterone (spironolactone, eplerenone) or epithelial sodium channels (amiloride) induces moderate diuresis. ◦ Arginine Vasopressin (AVP): → Released by posterior pituitary in response to increased intracellular osmolarity. → Stimulates V receptors → increases reabsorption of free water in distal tubules and collecting ducts. → In heart failure: AVP is elevated due to nonosmotic stimuli (decreased EAV, reduced left atrial compliance) → leads to edema and hyponatremia. ◦ Endothelin-1: → Potent peptide vasoconstrictor from endothelial cells. → Elevated in severe heart failure; contributes to renal vasoconstriction and sodium retention. ◦ Natriuretic Peptides (ANP, BNP): → ANP: Released by atrial distention. → BNP: Released when ventricular diastolic pressure rises. → Actions: \uparrow GFR, \downarrow proximal tubule Na+ reabsorption, \downarrow renin/aldosterone release, and dilation of arterioles/venules. → Clinical Limitation: In heart failure and cirrhosis, these are often insufficient to prevent edema due to increased resistance to their actions.

• Mechanism of Physiological Pathways (Figure 43-1): 1. Pathway A (Reduced Volume): \downarrow Extracellular fluid volume → \downarrow Cardiac output & \downarrow Effective arterial volume → Activation of Nonosmotic vasoconstriction, SNS, and RAAS → \uparrow Renal H_2O retention & \uparrow Renal Na^+ retention. 2. Pathway B (Reduced Resistance): \downarrow Systemic vascular resistance → \downarrow Effective arterial volume → Activation of Nonosmotic vasoconstriction, SNS, and RAAS → \uparrow Renal H_2O retention & \uparrow Renal Na^+ retention. 3. Clinical Conditions: High-output cardiac failure, Sepsis, Cirrhosis, Arterio/venous malformation, Pregnancy.

4. CLINICAL FEATURES

• General Presentation: ◦ Pitting: Edema is recognized by the persistence of an indentation of the skin after pressure. ◦ Subtle signs: Indentation from a stethoscope; rings fitting snugly; difficulty putting on shoes (worse in evening). ◦ Facial Edema: Most prominent in periorbital areas due to tissue laxity; most apparent upon awakening. ◦ Anasarca: Gross, generalized edema. ◦ Special Forms: Ascites and hydrothorax are considered special forms of edema.

• Distribution of Edema: ◦ Heart Failure: More extensive in the legs; accentuated in the evening (posture-dependent); presacral region if bedridden. ◦ Nephrotic Syndrome/Hypoalbuminemia: Generalized, but especially evident in soft tissues of eyelids and face; most pronounced in the morning. ◦ Cirrhosis: Initially localized to proximal areas (ascites) due to portal hypertension → later peripheral edema develops with severe hypoalbuminemia. ◦ Local Obstruction: Edema limited to one limb → venous or lymphatic obstruction. → Superior vena cava obstruction → face, neck, and upper extremities.

• Localized Edema (Lymphatic): ◦ Lymphedema: Result of lymphatic obstruction (e.g., filariasis, surgery, primary lymphedema). → Mechanism: \uparrow Intracapillary pressure + \uparrow Interstitial protein concentration → highly intractable.

• Other Specific Types: ◦ Myxedema (Hypothyroidism): Due to tissue deposition of hyaluronic acid. ◦ Pretibial Myxedema (Graves' disease): Nonpitting edema. ◦ Refeeding Edema: Occurs in starved patients when food is introduced → insulin release → increased tubular sodium reabsorption. ◦ Drug-Induced Edema: Caused by NSAIDs, cyclosporine, vasodilators (hydralazine, etc.), calcium channel blockers, thiazolidinediones, steroids, and others.

5. DIFFERENTIAL DIAGNOSIS

• Primary Differentiation Strategy: 1. Determine if edema is localized or generalized. 2. If localized: Identify local causes (e.g., venous/lymphatic obstruction). 3. If generalized: Check for hypoalbuminemia (Serum albumin < 3.0 g/dL). → If yes: Evaluate for cirrhosis, malnutrition, or nephrotic syndrome. 4. If no hypoalbuminemia: Assess for heart failure severity. 5. Determine urine output (assess for oliguria/anuria).

• Comparison of Major Causes (Table 43-1): 1. Cardiac: → History: Dyspnea, orthopnea, paroxysmal nocturnal dyspnea. → Physical Exam: Elevated JVP, S3 gallop, peripheral cyanosis, cool extremities, low pulse pressure. → Labs: \uparrow BUN/Creatinine ratio, \downarrow Sodium, \uparrow Natriuretic peptides. 2. Hepatic: → History: Ethanol abuse; dyspnea only if significant ascites. → Physical Exam: Ascites, JVP normal/low, BP lower than renal/cardiac, signs of liver disease (jaundice, palmar erythema, spider angiomata). → Labs: \downarrow Albumin, \downarrow Cholesterol, \uparrow Liver enzymes, hypokalemia, respiratory alkalosis. 3. Renal (CRF): → History: Chronic; uremic signs (metallic taste, restless legs). → Physical Exam: Elevated BP, hypertensive retinopathy, uremic fetor, pericardial friction rub. → Labs: \uparrow Creatinine/Cystatin C, albuminuria, hyperkalemia, metabolic acidosis, hypocalcemia, anemia (normocytic). 4. Renal (NS): → History: Childhood DM, plasma cell dyscrasias. → Physical Exam: Periorbital edema, hypertension. → Labs: Proteinuria (≥ 3.5 g/d), hypoalbuminemia (< 3.0 g/dL), hypercholesterolemia.

6. INVESTIGATIONS & DIAGNOSIS

  1. Cardiac Evaluation: Perform noninvasive tests (ECG, Echocardiography) and measure BNP or NT-proBNP.
  2. Renal Assessment: Perform Urinalysis to evaluate for nephrotic syndrome or renal failure.
  3. Hepatic Assessment: Order Liver Function Tests (LFTs) and serum albumin levels.
  4. Cyanosis Differentiation: If mechanism is obscure, perform spectroscopic examination of blood for abnormal hemoglobin types; determine PaO_2 and SaO_2.

7. MANAGEMENT & TREATMENT

  1. Primary Goal: Treat the underlying cause (e.g., heart failure, cirrhosis, renal disease).
  2. Neurohumoral Blockade: → Block conversion of Ang I to Ang II or block Ang II receptors → increase Na/water excretion. → Aldosterone Antagonists: Spironolactone or eplerenone. → Sodium Channel Blockers: Amiloride.
  3. Drug-Induced Edema Management: Identify and remove offending agents (Table 43-2). → NSAIDs & Cyclosporine (Renal vasoconstriction) → Direct arterial/arteriolar vasodilators (Hydralazine, Clonidine, Methyldopa, Guanethidine, Minoxidil) → Calcium channel antagonists → Thiazolidinediones → Steroid hormones (Glucocorticoids, Anabolic steroids, Estrogens, Progestins) → Immunotherapies (IL-2, OKT3).
  4. Lymphedema: Note that this is particularly intractable due to high interstitial protein concentration and increased capillary pressure.

8. PROGNOSIS & COMPLICATIONS

• Lymphedema: Highly intractable; results in persistent fluid retention. • Clubbing: May be reversible (e.g., after lung transplant for cystic fibrosis). • Nutritional Edema: Resolves with adequate diet, though refeeding edema may occur initially. • Hepatic Progression: Cirrhosis edema typically progresses from ascite to peripheral edema as liver function declines.

9. SPECIAL CONSIDERATIONS

• Pediatrics: Nephrotic syndrome can present in children (e.g., childhood DM, plasma cell dyscrasias). • Pregnancy: Recognized as a specific cause of edema. • Nutritional: Specific considerations for starvation and refeeding edema.

10. KEY PEARLS & CLINICAL TRAPS

• Cyanosis Timing: Cyanosis present since birth/infancy → likely congenital heart disease. • Cyanosis Differentiation: Massage/warming of extremity → abolishes peripheral cyanosis but NOT central cyanosis. • Clubbing & Cyanosis: Combination suggests right-to-left shunt (congenital heart) or pulmonary disease; isolated cyanosis without clubbing is not associated with these specific conditions. • Renal vs. Heart Failure: Renal edema has normal/increased cardiac output; heart failure edema typically occurs in dependent areas. • Refeeding Edema: Linked to insulin release → increased tubular sodium reabsorption. • Drug-Induced List (Table 43-2): Includes NSAIDs, Hydralazine, Clonidine, Methyldopa, Guanethidine, Minoxidil, Calcium channel antagonists, Thiazolidinediones, Steroid hormones, Cyclosporine, and Immunotherapies.

Reference Tables

TABLE 43-1 Principal Causes of Generalized Edema: History, Physical Examination, and Laboratory Findings

Harrison's 22e, p.281

ORGAN SYSTEM HISTORY PHYSICAL EXAMINATION LABORATORY FINDINGS
Cardiac Dyspnea with exertion prominent—often
associated with orthopnea—or paroxysmal
nocturnal dyspnea		 Elevated jugular venous pressure, ventricular (S) gallop;
3
occasionally with displaced or dyskinetic apical impulse;
peripheral cyanosis, cool extremities, low pulse pressure
when severe		 Elevated urea nitrogen-to-creatinine ratio
common; serum sodium often decreased;
elevated natriuretic peptides
Dyspnea uncommon, except if associated
with significant degree of ascites; most
often a history of ethanol abuse		 Frequently associated with ascites; jugular venous
pressure normal or low; blood pressure lower than
in renal or cardiac disease; one or more additional
signs of chronic liver disease (jaundice, palmar
erythema, Dupuytren’s contracture, spider angiomata,
male gynecomastia; asterixis and other signs of
encephalopathy) may be present
Renal (CRF) Usually chronic: may be associated with
uremic signs and symptoms, including
decreased appetite, altered (metallic or
fishy) taste, altered sleep pattern, difficulty
concentrating, restless legs, or myoclonus;
dyspnea can be present, but generally less
prominent than in heart failure		 Elevated blood pressure; hypertensive retinopathy;
uremic fetor; pericardial friction rub in advanced cases
with uremia		 Elevation of serum creatinine and
cystatin C; albuminuria; hyperkalemia,
metabolic acidosis, hyperphosphatemia,
hypocalcemia, anemia (usually
normocytic)
Childhood diabetes mellitus; plasma cell
dyscrasias		 Periorbital edema; hypertension

TABLE 43-2 Drugs Associated with Edema Formation Nonsteroidal anti-inflammatory drugs Antihypertensive agents

Harrison's 22e, p.282

  • Nonsteroidal anti-inflammatory drugs
  • Antihypertensive agents
  • Direct arterial/arteriolar vasodilators
  • Hydralazine
  • Clonidine
  • Methyldopa
  • Guanethidine
  • Minoxidil
  • Calcium channel antagonists
  • α-Adrenergic antagonists
  • Thiazolidinediones
  • Steroid hormones
  • Glucocorticoids
  • Anabolic steroids
  • Estrogens
  • Progestins
  • Cyclosporine
  • Growth hormone
  • Immunotherapies
  • Interleukin 2
  • OKT3 monoclonal antibody