Hyponatremia vs Hypernatremia
Both sodium imbalances present with altered mental status, but the fluid shift direction is opposite — and so is the neurological picture. Picking the wrong IV fluid or correcting too fast can cause osmotic demyelination or cerebral edema, turning a fixable lab value into permanent brain damage.
Side-by-side comparison
- Hypotonic serum
- water shifts INTO cells
- SIADH, water intoxication
- Thiazides
- HF dilution
- polydipsia
- Hypertonic serum
- water shifts OUT of cells
- Diabetes insipidus
- dehydration
- Hypertonic IV fluids
- impaired thirst
- Confusion, lethargy, headache (cells swell then coma)
- Muscle weakness, cramps, hyporeflexia
- ★Twitching, hyperreflexia, spasticity
- Restlessness, irritability (cells shrink then coma)
- Serum Na⁺ < 135 mEq/L
- May appear euvolemic / hypervolemic
- Serum Na⁺ > 145 mEq/L
- ↑ urine specific gravity (except DI)
- Seizure precautions
- neuro checks q1h
- Serum Na⁺ q2–4h during correction
- strict I&O
- Monitor fluid status
- offer water
- Serum Na⁺ q2–4h
- neuro checks, daily weight
- ★Severe/seizures: 3% saline via pump
- Mild: fluid restriction
- treat cause
- Replace free water: D5W or 0.45% NS
- ★Desmopressin for diabetes insipidus
- Follow fluid restriction
- avoid excess water
- Report headache, confusion, nausea
- Drink adequate water
- don't ignore thirst
- Report restlessness, dry mouth
- ★Seizures from cerebral edema
- Obtundation, falling level of consciousness
- Seizures if Na⁺ > 160 (acute severe)
- Rapid level of consciousness decline then coma
- Over-fast correction then ODS / CPM
- Limit: raise Na⁺ ≤ 8 mEq/L per 24 hr
- Over-fast correction then cerebral edema
- Limit: lower Na⁺ ≤ 10–12 mEq/L/24 hr
Hyponatremia (< 135 mEq/L)
- Hypotonic serum
- water shifts INTO cells
- SIADH, water intoxication
- Thiazides
- HF dilution
- polydipsia
Hypernatremia (> 145 mEq/L)
- Hypertonic serum
- water shifts OUT of cells
- Diabetes insipidus
- dehydration
- Hypertonic IV fluids
- impaired thirst
Hyponatremia (< 135 mEq/L)
- Confusion, lethargy, headache (cells swell then coma)
- Muscle weakness, cramps, hyporeflexia
Hypernatremia (> 145 mEq/L)
- ★Twitching, hyperreflexia, spasticity
- Restlessness, irritability (cells shrink then coma)
Hyponatremia (< 135 mEq/L)
- Serum Na⁺ < 135 mEq/L
- May appear euvolemic / hypervolemic
Hypernatremia (> 145 mEq/L)
- Serum Na⁺ > 145 mEq/L
- ↑ urine specific gravity (except DI)
Hyponatremia (< 135 mEq/L)
- Seizure precautions
- neuro checks q1h
- Serum Na⁺ q2–4h during correction
- strict I&O
Hypernatremia (> 145 mEq/L)
- Monitor fluid status
- offer water
- Serum Na⁺ q2–4h
- neuro checks, daily weight
Hyponatremia (< 135 mEq/L)
- ★Severe/seizures: 3% saline via pump
- Mild: fluid restriction
- treat cause
Hypernatremia (> 145 mEq/L)
- Replace free water: D5W or 0.45% NS
- ★Desmopressin for diabetes insipidus
Hyponatremia (< 135 mEq/L)
- Follow fluid restriction
- avoid excess water
- Report headache, confusion, nausea
Hypernatremia (> 145 mEq/L)
- Drink adequate water
- don't ignore thirst
- Report restlessness, dry mouth
Hyponatremia (< 135 mEq/L)
- ★Seizures from cerebral edema
- Obtundation, falling level of consciousness
Hypernatremia (> 145 mEq/L)
- Seizures if Na⁺ > 160 (acute severe)
- Rapid level of consciousness decline then coma
Hyponatremia (< 135 mEq/L)
- Over-fast correction then ODS / CPM
- Limit: raise Na⁺ ≤ 8 mEq/L per 24 hr
Hypernatremia (> 145 mEq/L)
- Over-fast correction then cerebral edema
- Limit: lower Na⁺ ≤ 10–12 mEq/L/24 hr
★ marks the fact that sets a column apart.
Clinical Pearl
Low sodium, swollen brain, seizures; high sodium, shrunken brain, agitation — correct either one slowly.
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