CAUSES
. Sodium excess - total body sodium increased
. Oral - improperly mixed infant formula, salt given as punishment or as a prank, sea water ingestion
. IV - NaCl or NaHCO3 during cardiopulmonary resuscitation, intrauterine NaCl for abortion
. Water deficit - total body sodium normal
. Decreased intake: e.g., thirst, decreased access to water
. Increased urine water loss, e.g., diabetes insipidus
. Increased insensible water loss, e.g., fever, hyperventilation, hypermetabolic state
. Hypotonic fluid loss - total body sodium decreased
. Loss of fluid containing sodium - without adequate water replacement
. Urinary loss
. Osmotic diuretics
. Diabetes mellitus
. Diuresis from acute tubular necrosis (ATN) or from relief of acute urinary obstruction
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DIFFERENTIAL DIAGNOSIS
β’ Diabetes insipidus
β’ Hyperosmotic coma
β’ Salt ingestion
β’ Hypertonic dehydration
LABORATORY
. Serum Na > 150 to 170 mEq/L (> 150-170 mmol/L) - usually dehydration
. Serum Na > 170 mEq/L (> 170 mmol/L) - usually diabetes insipidus
. Serum Na > 190 mEq/L (> 190 mmol/L) - usually chronic salt ingestion
* Diabetes insipidus : Urine osmolality less than serum osmolality, Urine sodium usually low, Polyuria, Neurogenic vs. nephrogenic diabetes insipidus
* Hyperosmolar coma : Blood sugar elevated, Decreased urine output, Increased urine osmolality
* Salt ingestion : . Increased urine Na, Increased urine osmolality
* Hypertonic dehydration : Decreased urine sodium, Increased urine osmolality
SPECIAL TESTS
β’ Water deprivation (with diabetes insipidus urine osmolality does not increase when hypernatremic)
β’ Antidiuretic hormone (ADH) stimulation (with nephrogenic diabetes insipidus urine osmolality does not increase after ADH or DDAVP)
IMAGING CAT scan or MRI in diabetes insipidus - to rule out craniopharyngioma, tumor or median cleft syndrome
DIAGNOSTIC PROCEDURES History, physical, laboratory studies, family history for NDI