euvolemic

Euvolemia is the clinical and physiologic state in which the extracellular fluid (ECF) volume is normal. In euvolemia there are no signs of dehydration or fluid overload, and body weight remains relatively stable with no edema or overt signs of impaired perfusion attributable to volume abnormalities.

Physiology and determinants of euvolemia center on the balance between water and solute intake and loss. Key regulators include antidiuretic hormone (vasopressin), the renin–angiotensin–aldosterone system, and natriuretic peptides, which together maintain a stable effective circulating volume. Euvolemia can occur even when there are disturbances in water balance that alter sodium concentration, such as hyponatremia, if salt content tracks with water to preserve normal volume.

Clinical significance and context: The term is frequently used when evaluating hyponatremia. Euvolemic hyponatremia describes hyponatremia with a clinically normal fluid status. Common etiologies include syndrome of inappropriate antidiuretic hormone secretion (SIADH), hypothyroidism, adrenal insufficiency, and primary polydipsia. It is contrasted with hypovolemic hyponatremia (volume depletion) and hypervolemic hyponatremia (volume overload with edema, as in heart failure or cirrhosis).

Diagnosis and assessment: Evaluation relies on history and examination for signs of dehydration or edema, supplemented by laboratory testing. Useful tests include serum osmolality and sodium, urine osmolality and urine sodium, and targeted endocrine studies (such as thyroid function tests and morning cortisol) to identify underlying causes.

See also: fluid balance, hyponatremia, hypovolemia, hypervolemia.