Management is predicated on an understanding of the etiology of a patient's hyponatremia, the severity of the presentation, and the duration of the hyponatremia. While hyponatremia can be life threatening when severe and in select situations requires rapid correction, overly rapid correction of long-standing hyponatremia can result in devastating neurologic consequences due to central pontine myelinolysis.
Hyponatremia may come about from abnormal levels of serum sodium or intravascular volume or both. True hyponatremia is marked by concurrent hypotonicity with a serum osmolality <280 mOsm/kg. Serum sodium <134 mmol/L with normal or elevated serum osmolarity indicates pseudohyponatremia (hyperlipidemia or hyperparaproteinemia) or the presence of an osmotically active substance such as mannitol or glucose. With true hyponatremia, patients either have normal renal water excretion (as measured by urine osmolarity) as is seen in primary polydipsia (or administration of dilute infant formula or excessive use of tap water enemas) or a reset osmostat or impaired water excretion. Impaired water excretion can be due to endocrinologic abnormalities such as hypothyroidism and adrenal insufficiency, and these should be excluded.
Renal excretion of sodium is then evaluated. Low levels (<20 mmol/L) of urine excretion indicate hypovolemia or intravascular depletion states despite total body volume overload as is seen in congestive heart failure, cirrhosis, and nephrotic syndrome. Inappropriately high rates of urinary sodium excretion (>40 mmol/L despite serum hyponatremia) indicate the syndrome of inappropriate antidiuretic hormone (SIADH), which can be due to medications or renal salt wasting. Selective serotonin reuptake inhibitors (SSRIs), anticonvulsants, alcohol abuse, and opioids are frequently implicated in inappropriate antidiuretic hormone levels. Intracranial injury can lead to cerebral salt wasting, which causes hyponatremia, intravascular volume depletion, and a concentrated urine with natriuresis. Diuretics are another frequent cause of drug-induced hyponatremia due to their effects on intravascular volume, sodium retention in the kidneys, or on the aldosterone system.
E87.1 – Hypo-osmolality and hyponatremia
89627008 – Hyponatremia
- Pseudohyponatremia (hyperlipidemia, hyperproteinemia)
- Dilutional hyponatremia (hyperglycemia, mannitol, glycine, sorbitol, alcohol)
- Contrast administration
- Diarrhea / vomiting
- Cerebral salt wasting syndrome
- Beer potomania
- Psychogenic polydipsia
- Advanced renal failure
- Nephrotic syndrome
- Syndrome of inappropriate antidiuretic hormone
- Postoperative hyponatremia
- Congestive heart failure
- Adrenal insufficiency (primary, secondary)
- Multiple myeloma
- Incorrect or inappropriate volumes of intravenous fluid (iatrogenic)