Hypernatremia
High sodium is usually a water problem before it is a sodium problem.
Think water balance first
Hypernatremia reflects too little water relative to body sodium and potassium. Start with baseline, acuity, neurologic symptoms, intake, and the patient's ability to sense and respond to thirst.
Build the loss story
Fever, tachypnea, diarrhea, osmotic diuresis, diuretics, polyuria, and impaired renal concentrating ability can all produce water loss when replacement does not keep up.
Volume status is related — not identical
Hypernatremia can coexist with volume depletion, but the sodium concentration primarily reflects water balance. Do not use the sodium value alone as a direct measure of intravascular volume.
Urine can reveal the mechanism
When the cause is unclear, urine volume and urine osmolality help determine whether the kidneys are appropriately conserving water. High-volume dilute urine raises a different question than GI loss with concentrated urine.
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