Disorders of Water and Sodium Balance: Hyponatremia

Abstract

Disorders of water and sodium balance are common in clinical practice. To better assess them, we must have a clear understanding of water-electrolyte homeostasis and renal function. The following review goes over practical equations necessary for electrolyte balance analysis as well as the foundations of renal physiology. Emphasis is placed on the understanding of sodium transport and its physiologic and pharmacologic regulation. In addition, we explore the most common electrolyte imbalance affecting up to 28% of hospitalized patients: hyponatremia (ie, low sodium concentration). Hyponatremia has been found in several acute and chronic clinical scenarios including postoperative, drug-induced, and exercise-associated hyponatremia. However, it is not uncommon to find this disorder coexisting with other diseases such as syndrome of inappropriate secretion of antidiuretic hormone (SIADH), acquired immunodeficiency syndrome (AIDS), cancer, and in rare cases, hypothyroidism. To better understand this disorder, the etiology, diagnosis with clinical manifestations and laboratory values, and treatment options are explored. This review contains 9 figures, 6 tables, and 52 references. Key Words: aldosterone, antidiuretic hormone, body fluids, electrolyte balance, hyponatremia, hypovolemia, osmolality, sodium transport, vasopressin