This document discusses hypernatremia, defined as a serum sodium level greater than 150 mEq/L. It describes the normal extracellular and intracellular fluid compartments and how they are affected by hypernatremia. Clinical signs of hypernatremia range from restlessness to seizures and death depending on the serum osmolality level. Common causes include inadequate water intake, excessive sodium intake, renal or GI losses. Treatment involves volume repletion first with isotonic fluids followed by a gradual decrease in sodium levels with hypotonic fluids over 1-2 days. Free water deficits are calculated to determine fluid replacement volumes needed.

1. Hypernatremia
[Na]> 150 mEq/L

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

3. Effects of Hypernatremia
on the Brain and Adaptive
Responses.

4. Clinical Signs of Hypernatremic
States Related to Serum Osmolality
Osmolality (mOsm/kg) Manifestations
350–375 Restlessness, irritability
375–400 Tremulousness, ataxia
400–430 Hyperreflexia, twitching,
spasticity
>430 Seizures and death

5. Causes of Hypernatremia
*Likely or important ED diagnostic considerations.
Inadequate water intake* GI loss*
Inability to obtain or swallow water Vomiting, diarrhea, intestinal fistula
Renal loss
Impaired thirst drive
Central diabetes insipidus
Increased insensible loss
Impaired renal concentrating ability
Excessive sodium Osmotic diuresis (multiple causes)*
Iatrogenic sodium administration – Hypercalcemia
– Sodium bicarbonate – Decreased protein intake
– Hypertonic saline – Prolonged, excessive water intake
– Sickle cell disease
Accidental/deliberate ingestion of large – Multiple myeloma
quantities of sodium – Amyloidosis
– Substitution of salt for sugar in infant – Sarcoidosis
formula or tube feedings – Sjögren syndrome
– Salt water ingestion or drowning – Nephrogenic diabetes insipidus
Mineralocorticoid or glucocorticoid – Congenital
excess* Drugs/medications
– Primary aldosteronism Alcohol, lithium, phenytoin, propoxyphene,
sulfonylureas, amphotericin, colchicine
– Cushing syndrome
Skin loss
– Ectopic ACTH production
Burns, sweating
Peritoneal dialysis
Essential hypernatremia
– Loss of water in excess of sodium

6. 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).

7. 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)

8. Treatment
The 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.

10. Calculation of Free Water Deficit
measured[Na ]
TBW 0.6 1
desired[Na ]
Replacement Volume = TBW deficit × 1/(1－X)
X= [Na+] of resuscitation fluid / [Na+] of isotonic saline

11. 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

12. 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