Hyponatremia - Causes and Symptoms

Definition

Hyponatremia is defined as a plasma sodium level below 135 mEq / L (135 mmol / L).

The degree and speed with which this electrolyte imbalance is created determine the various clinical features of hyponatremia. A rapid reduction (within 24-48 hours) of the sodium concentration can be associated with symptoms ranging from mild anorexia, headache and muscle cramps to a significant alteration in mental status, including confusion, convulsions and coma.

Hyponatremia reflects an excess of total body water compared to the total body content of sodium (Na); in general, the amount of Na is increased in hypervolemic patients, normal in euvolemic subjects and low in hypovolemic patients.

Causes of frequent hyponatremia include the use of diuretics, diarrhea, congestive heart failure and kidney disease.

Hypovolemic hyponatremia

Hypovolaemic hyponatremia develops following the loss of sodium and total body water and their replacement with inappropriately hypotonic liquids. Sodium can be lost by renal or extra-renal.

Extra-renal modalities include gastro-intestinal depletion (diarrhea and vomiting), excessive sweating and leakage from the third compartment (ascites, burns, pancreatitis, peritonitis, etc.). Renal losses, on the other hand, may depend on nephropathies with salt loss (eg interstitial nephritis, partial urinary tract obstruction and polycystic kidney disease), therapies with diuretics and mineralocorticoid deficiency.

Hypervolemic hyponatremia

Hypervolemic hyponatremia occurs in patients with excessive levels of total body sodium. It is a possible consequence of nephropathy (nephrotic syndrome, acute and chronic renal failure), liver cirrhosis and heart failure.

Euvolemic hyponatremia

Euvolemic hyponatremia, on the other hand, is characterized by a normal level of total body sodium and a total excess of free water. This occurs in patients taking excess fluids (psychogenic polydipsia and intravenous administration of hypotonic solutions) or suffering from adrenal insufficiency (as in Addison's disease), hypothyroidism, and ADH inappropriate secretion syndrome. Sometimes, it is the result of emotional stress, neuropsychiatric and pulmonary pathologies, malignant tumors and post-operative pain (from major surgery). Euvolemic hyponatraemia may also result from the use of pharmacological agents (including diuretics, chlorpropamide, clofibrate, carbamazepine and antidepressants / antipsychotics).

The syndrome of inappropriate ADH secretion (SIADH) is another cause of euvolemic hyponatremia; depends on an increase in the secretion of arginine vasopressin, the consequence of which is an impairment of water excretion.