Physiological Basis of Lower Limb Edema

Abstract

Edema can be defined as the accumulation of excess fluid in the interstitial or intercellular spaces of the body. Edema is usually caused due to disturbances in the mechanisms that govern exchange of water and solutes between the intravascular and the interstitial fluid compartments, at the capillary microcirculation level. The capillary blood flow and fluid exchange are compactly regulated by intrinsic and extrinsic apparatuses like capillary endothelial substances and autonomic innervations, respectively. The Starling forces, namely hydrostatic and osmotic pressure, play fundamental role in determining the fluid movements across the capillary wall. Increased capillary hydrostatic pressure or increased interstitial osmotic pressure favors outward fluid shift from capillaries—a process named filtration, while decreased capillary hydrostatic pressure or decreased interstitial osmotic pressure favors absorption, where fluid moves into the capillaries. Prolonged standing, reduced physical activity, consumption of low protein diet, pregnancy, and rapid ascent to high altitudes are some of the physiological causes of peripheral edema. On the other hand, endocrine disorders like myxedema, Cushing syndrome, and failure of vital organs like the heart, liver, and kidneys contribute to the systemic pathological etiologies of edema formation. Localized limb pathologies like lymphatic obstruction, deep vein thrombosis, dermatitis, and lipedema should also be kept in mind while discussing the causes of peripheral edema. Drugs like calcium channel blockers, corticosteroids, estrogens, progesterones, and vasodilators like minoxidil and hydralazine are known to cause peripheral edema as one of their adverse effects. A thorough history and relevant physical examination supplemented with laboratory and radiological investigations constitute the cornerstone in the diagnosis and management of patients presenting with lower limb edema in a clinical setting.