Hypernatremia[Na]> 150 mEq/L

Extracellular-Fluid and Intracellular-Fluid Compartments under Normal Conditions and during States of Hypernatremia.

Effects of Hypernatremia on the Brain and Adaptive Responses.

Clinical Signs of Hypernatremic States Related to Serum Osmolality

Osmolality (mOsm/kg) Manifestations350–375 Restlessness, irritability 375–400 Tremulousness, ataxia 400–430 Hyperreflexia, twitching,

spasticity>430 Seizures and death

Causes of Hypernatremia*Likely or important ED diagnostic considerations.

Inadequate water intake*   

Inability to obtain or swallow water   

Impaired thirst drive   

Increased insensible loss

Excessive sodium   

Iatrogenic sodium administration     – Sodium bicarbonate     – Hypertonic saline   

Accidental/deliberate ingestion of large quantities of sodium     

– Substitution of salt for sugar in infant formula or tube feedings     

– Salt water ingestion or drowning   

Mineralocorticoid or glucocorticoid excess*     

– Primary aldosteronism     – Cushing syndrome     – Ectopic ACTH production   

Peritoneal dialysis     – Loss of water in excess of sodium

GI loss*     

Vomiting, diarrhea, intestinal fistula   

Renal loss     

Central diabetes insipidus     

Impaired renal concentrating ability     

Osmotic diuresis (multiple causes)*        – Hypercalcemia        – Decreased protein intake        – Prolonged, excessive water intake        – Sickle cell disease        – Multiple myeloma        – Amyloidosis        – Sarcoidosis        – Sjögren syndrome        – Nephrogenic diabetes insipidus        – Congenital   

Drugs/medications     

Alcohol, lithium, phenytoin, propoxyphene, sulfonylureas, amphotericin, colchicine   

Skin loss     

Burns, sweating

Essential hypernatremia

Most hypernatremia encountered in the ED is related to severe volume loss.

In otherwise healthy patients, hypovolemia leads to conservation of free water by the kidneys that results in low urine output (<20 mL/h) with high osmolality (usually >1000 mOsm/kg water).

Diabetes Insipidus

Diabetes insipidus is characterized by the failure of central or peripheral ADH response.

Urine osmolality is low (200 to 300 mOsm/kg, with urinary [Na+] of 60 to 100 mEq/kg)

TreatmentThe cornerstone of treatment is volume repletion.

Volume should be replaced first with NS or lactated Ringer's solution.

Some practitioners inappropriately fear using NS solution from concern that an [Na+] of 154 mEq/L exceeds normal serum [Na+]. However, in most hypernatremic states, there is a total body [Na+] deficit, and the use of NS allows a more gradual decrease in serum [Na+].

Once perfusion has been established, the solution should be converted to 0.45% saline or another hypotonic solution until the urine output is at least 0.5 mL/kg/h.

The reduction in [Na+] should not exceed 10~15 mEq/L per day.

Calculation of Free Water Deficit

1][Na desired

][Na measured0.6TBW

Replacement Volume = TBW deficit × 1/(1－ X)

X= [Na+] of resuscitation fluid / [Na+] of isotonic saline

70 公斤的成人，抽血發現 [Na+] 160 mEq/L

計算式：TBW deficit = 0.6 ×70× [160/140 － 1]= 6 L

若使用 0.45NaCl 做為輸液Replacement volume = 6 × 1/ (1 － ½)=12 L

水分缺損要在 48 小時 補足點滴速度大約每小時要 250 mL

Reference

Fluids and Electrolytes, Tintinalli‘s Emergency Medicine 2010:117-121

Hypernatremia, NEJM 2000; 342:1493-1499

Hyponatremia, NEJM 2000; 342:1581-158

Hypertonic and hypotonic Conditions, The ICU Book 2007: 595-602