Euvolemia

Euvolemia is the physiological state in which the body's extracellular fluid volume is normal and appropriately distributed among compartments, allowing for adequate tissue perfusion and oxygenation. It denotes neither dehydration due to fluid loss nor fluid overload. In clinical practice, euvolemia is a target in fluid management and is evaluated across medicine, surgery, nephrology, and critical care settings.

Fluid balance is regulated by thirst, renal excretion, and hormonal systems that respond to changes in volume and osmolality. Key regulators include antidiuretic hormone (vasopressin), the renin-angiotensin-aldosterone system, and natriuretic peptides. Maintaining euvolemia requires appropriate balancing of water intake and renal handling of water and solutes, guided by serum osmolality and electrolytes.

Assessment of euvolemia combines physical examination and laboratory data. Clinicians look for signs of volume depletion or overload, such as changes in skin turgor, mucous membranes, blood pressure, heart rate, and jugular venous pressure, alongside laboratory tests of electrolytes, plasma osmolality, and urine studies. In the context of hyponatremia, distinguishing euvolemic states from hypovolemic or hypervolemic conditions helps identify etiologies such as syndrome of inappropriate antidiuretic hormone secretion (SIADH), hypothyroidism, or adrenal insufficiency.

Management aims to maintain or restore normal fluid balance by treating the underlying cause and avoiding unnecessary fluid shifts. In true euvolemia, no routine fluid restriction or diuresis is indicated. When euvolemic hyponatremia occurs, management focuses on addressing the underlying disorder, cautious fluid restriction, and, in severe cases, careful correction of sodium under supervision.