Hypernatremia
The confused elderly patient who "just stopped drinking water" after hip surgery may not have a neuro problem — they may have a sodium of 152 mEq/L that nobody checked.
Core Concept
Hypernatremia is serum sodium >145 mEq/L. The most common cause in hospitalized clients is free water deficit — the patient isn't drinking enough, has insensible losses (fever, burns, mechanical ventilation), or is receiving hypertonic solutions. Diabetes insipidus (central or nephrogenic) causes massive dilute urine output with rising serum sodium because ADH is absent or ineffective. The hallmark presentation is neurological: restlessness and irritability progress to confusion, lethargy, seizures, and coma as water shifts out of brain cells, causing cellular shrinkage. Thirst is a key early sign but is unreliable in sedated, intubated, or cognitively impaired clients. Assessment includes strict I&O, daily weights, urine specific gravity (elevated >1.030 in dehydration, paradoxically low <1.005 in diabetes insipidus), and monitoring serum osmolality (elevated >295 mOsm/kg). Correction must be gradual — sodium should decrease no faster than 10-12 mEq/L per 24 hours. Rapid correction causes water to rush into shrunken brain cells, producing cerebral edema. The primary nursing intervention is administering hypotonic IV fluids (0.45% NaCl or D5W) as prescribed and encouraging oral free water intake when safe. Seizure precautions are essential for significantly elevated sodium levels.
Watch Out For
Don't confuse hypernatremia (dry, flushed, restless, thirsty) with hyponatremia (confused, nauseated, headache — which can be hypovolemic, euvolemic, or hypervolemic) — both cause neuro changes but the sodium and osmolality directions are opposite. Students mix up the correction danger: too-fast correction of hypernatremia causes cerebral edema, while too-fast correction of hyponatremia causes osmotic demyelination. In diabetes insipidus the urine is dilute despite high serum sodium — that mismatch is the diagnostic clue.
Clinical Pearl
Hypernatremia = dried-out brain cells. Think raisins. Correct slowly or those raisins swell into grapes too fast and you get cerebral edema.
Test Your Knowledge
3 quick questions — see how well you understood Hypernatremia