Hypernatremia - Differential Diagnosis and Treatment

Hypernatremia is almost always due to unreplaced water loss (free water deficit).

The differential can be broadly placed into 4 categories.

Diagnosis is primarily based on history, exam, and urine osm (in DI; high dilute urine output is a clue).

1) ↓ Water Intake, Dehydration: neurologic disease, water unavailable

2) Osmotic Diuresis: HHS, post-obstructive

3) Diabetes Insipidus: neurogenic, nephrogenic

4) ↑ Salt Intake: salt water, hyper/isotonic saline

Treatment:

Treatment of hypernatremia can also be complex and varies with chronicity and severity.

 • Start by calculating the free water deficit (FWD) = Total Body Water (TBW) x (([Na] / 140) - 1)

 • Total body water is 50-60% of patient weight (eg 0.5-0.6 x pt weight).

 • Generally, the treatment will involve resuscitation with isotonic fluids followed by free water.

 • Free water can be delivered with D5 fluids or enteral free water flushes.

 • Rapid correction of chronic hypernatremia puts patients at risk for cerebral edema and herniation.

 • The maximum rate of correction should not exceed 12 mEq/L in a 24-hour period.



Dr. Meredith Greer @EmmGeezee



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