Edema vs. Effusions: Pathophysiologic Mechanisms

• Edema is fluid accumulation in interstitial tissues, while effusions are fluid accumulation in body cavities
• Cardiovascular, renal, or hepatic dysfunction can disrupt fluid balance, causing edema or effusions

Pathophysiologic Mechanisms of Edema

• Increased hydrostatic pressure forces fluid out of capillaries into tissues
• Impaired venous return raises hydrostatic pressure

Impaired Venous Return Examples

• Congestive heart failure (CHF) results in blood pooling, raising hydrostatic pressure
• Constrictive pericarditis impairs venous return by compressing the heart
• Ascites, due to liver disease or heart failure, increases venous pressure causing fluid buildup in the peritoneal cavity
• Venous obstruction can be caused by thrombosis, tumors, or external compression, which can block veins, leading to localized edema
• Lower extremity inactivity slows venous return, leading to leg swelling

Arteriolar Dilation

• Arteriolar dilation raises capillary pressure, leading to fluid leakage
• Excessive vasodilation can also drop effective arterial blood volume and cause edema
• Heart failure causes compensatory vasodilation, increasing capillary pressure
• Neural humoral dysregulation causes vasodilation, increasing capillary pressure
• Activation of SNS, RAAS, and ADH release can lead to fluid leaking into the interstitial space, causing edema
• Excessive vasodilation expands vascular space, lowering pressure and flow in arteries
• Cirrhosis leads to excessive splanchnic vasodilation, triggering RAAS and causing peripheral edema and ascites

Lymphatic Obstruction ("Lymphedema")

• Lymphatic obstruction occurs when the lymphatic system cannot drain excess interstitial fluid
• Inflammation of the lymphatic vessels can impair the fluid drainage
• Neoplastic obstruction occurs when tumor block lymphatic drainage
• Carcinoma in lymph nodes impairs drainage
• Post-surgical obstruction disrupts drainage
• Breast cancer surgery, including lymph node dissection, causes chronic arm edema
• Post-irradiation damage scars lymphatic vessels, reducing their function

Sodium Retention

• Sodium retention occurs where excess sodium leads to water retention, increasing blood volume and hydrostatic pressure
• Excessive salt intake in individuals with kidney dysfunction overwhelm sodium regulation
• Renal insufficiency causes failing kidneys to not excrete sodium properly, leading to fluid overload
• Increased tubular sodium reabsorption can be caused by renal hypoperfusion

Inflammation (Acute & Chronic)

• Inflammation increases vascular permeability, allowing fluid and proteins to leak into tissues
• Infections, burns, or trauma causes capillary leakage, causing localized edema
• Chronic inflammation, like rheumatoid arthritis, disrupts normal fluid regulation
• Angiogenesis can create leaky capillaries, contributing to edema

Reduced Plasma Osmotic Pressure (Hypoproteinemia)

• Reduced plasma osmotic pressure is primarily driven by albumin, a protein that keeps fluid inside blood vessels
• Conditions that result in protein loss occurs in protein-losing enteropathy
• Liver cirrhosis occurs when the liver cannot produce albumin, reducing plasma oncotic pressure
• Malnutrition causes severe protein deficiency, lowering the oncotic pressure
• Protein-losing gastroenteropathy, also causes protein loss

Types and Morphology of Edema

• Subcutaneous edema is often seen in lower extremities
• Pitting edema occurs when pressure is applied and an indentation remains due to excess fluid
• Subcutaneous edema can indicate heart failure, kidney disease, or venous insufficiency
• Periorbital edema occurs as swelling around the eyes
• Periorbital edema is often seen in nephrotic syndrome due to protein loss
• The periorbital region is vulnerable due to tissue and skin in the area

Myxedema (Hypothyroid-Related Edema)

• Myxedema is seen in hypothyroidism
• Glycosaminoglycans accumulate in tissues, drawing in water, due to impaired metabolism
• Appearance include a waxy, swollen face, legs, tongue
• Primary hypothyroidism is due to thyroid dysfunction
• Secondary causes include pituitary dysfunction

Pulmonary Edema

• Pulmonary edema is characterized by pink fluid in alveolar spaces
• Pulmonary edema is caused by elevated hydrostatic pressure due to left heart failure and decreased colloid osmotic pressure
• Symptoms include blood-tinged sputum due to RBC leakage into alveoli

Brain Edema

• Increased intracranial pressure disrupts brain function
• Brain edema can be caused by trauma, stroke, and infections

Effusions

• Effusions are fluid in body cavities
• Pleural effusion is fluid in the lungs
• Pericardial effusion is fluid around the heart
• Peritoneal effusion (ascites) is fluid in the abdominal cavity and is common in cirrhosis

Pulmonary Edema in Histology

• In congestive heart failure, lung tissue shows pink-staining fluid in alveolar spaces
• Chronic pulmonary edema occurs when macrophages ingest RBCs, forming hemosiderin-laden macrophages
• Hemosiderin suggests chronic congestion or prior edema episodes