Diagnosis

Hypernatremia

Etiology

Cause [chb][36w]

1. Hypernatremic dehydration (urine, sweat, GI): water loss greater than sodium loss

   • Diarrhea

   • Breastfeeding difficulties

   • Burns

   • Diuretics

   • Diabetes mellitus (hyperglycemia causing osmotic diuresis)

   • Diabetes insipidus

   • Diaphoresis

   • Fistula

   • Athletes who refrain from drinking during heavy exercise in hot conditions

2. Excessive salt ingestion (euvolemia)

   • Supersaturated salt solution (salt poisoning)

   • Infants, mentally or physically disabled individuals who cannot express thirst

   • Hospitalized patients with under-replaced fluid or over-replaced sodium administration

3. Hypervolemic hypernatremia: edematous hypernatremia

   • Positive water balance in which increased fluid retention in response to excessive sodium

   • Most often seen in critically ill patients

   • Associated with hypoalbuminemia and azotemia

Pathophysiology [36w][zme]

1. Sodium maintain extracellular fluid volume

2. Severity of hypernatremia is associated with cellular shrinkage (crenation)

3. Two tablespoons of salt (30 g) can rapidly elevate blood [Na+] depending on bodyweight [36w]

4. Hypernatremia --> increased plasma osmolality --> regulatory responses:

   • Thirst response

   • ADH secretion

   • Result: water conservation and concentrated urine

Complications [zme]

• Seizure

• Cerebral edema (if rapid correction of hypernatremia)

• Subarachnoid or subdural hemorrhage

• Dural sinus thrombosis

Epidemiology

Incidence per 100.000 [chb][b64][tnc]

Approach

• Blood test: serum osmolality, plasma osmolality, creatinine, BUN, aldosterone, cortisol, antidiuretic hormone, and corticotropin (ACTH) levels

• Urine: osmolality, urine sodium levels

• CT caput

Treatment

1. Treatment goal: [zme]

   • Correct the serum sodium by maxiumum 12 meq in 24 hours

   • Correct the intravascular volume

2. Hypernatremic dehydration:

   • Stable circulation: Hypotonic fluid IV

   • Unstable circulation: Isotonic fluid IV

3. Excessive salt ingestion (euvolemia):

   • Hypotonic fluid IV

   • Sodium depleting diuretics

4. Calculating the free water deficit by the following formulas: [zme]

   • Total Body Water[0.6 in men and 0.5 in women x body weight(kg)] x [(plasma sodium/140) -1]

   • 4ml x bodyweight x (desired change in serum sodium meq/L)

   • Children: Water deficit (in L) = [(current Na level in mEq/L - 145 mEq/L)/145 mEq/L)] × 0.6 X weight (in kg)

Differential diagnoses

Cirrhosis, Clostridium tetani, Colovesical fistula, Congenital adrenal hyperplasia, Cushing syndrome, Diabetes insipidus, Diabetes mellitus, Diarrhea, Drug side effects, Hyperaldosteronism, Hyperkalemia, Hyperphosphatemia, Hyperventilation, Hypocalcemia, Hypocapnia, Hypokalemia, Hypomagnesemia, Hyponatremia, Hypoparathyroidism, Hypovolemia, Milk-alkali syndrome, Renal artery stenosis