Sodium Imbalance: Hyponatremia vs Hypernatremia — Causes, Neuro Signs, Correction
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.
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- Hypotonic: water shifts INTO cells
- SIADH, HF dilution
- Thiazides, psychogenic polydipsia
- Hypertonic: water shifts OUT of cells
- Diabetes insipidus, dehydration
- Hypertonic IV fluids, impaired thirst
- Confusion, lethargy
- Muscle cramps, hyporeflexia
- Headache, nausea (cells swell)
- ★Twitching, hyperreflexia, spasticity
- Restlessness, irritability (cells shrink)
- Confusion, lethargy
- Thirst, dry sticky mucosa
- Serum Na⁺ < 135 mEq/L
- Serum osmolality < 275
- Serum Na⁺ > 145 mEq/L
- ↑ urine specific gravity (except DI)
- Seizure precautions
- Frequent neuro checks
- Serum Na⁺ q2–4h during correction
- Fluid restriction, strict I&O
- Seizure precautions
- Offer free water, daily weight
- Serum Na⁺ q2–4h during correction
- Frequent neuro checks
- ★Severe/seizures: 3% saline via pump
- Mild: fluid restriction
- Replace free water: D5W or 0.45% NS
- ★Desmopressin for diabetes insipidus
- Follow fluid restriction
- Avoid excess water intake
- Report headache, confusion, nausea
- Drink adequate water
- Don't ignore thirst
- Report restlessness, dry mouth
- ★Seizures from cerebral edema
- ↓ LOC progressing to coma
- Seizures if Na⁺ > 160
- ↓ LOC progressing to coma
- Too-fast correction: ODS (CPM)
- Limit: raise Na⁺ ≤ 8 mEq/L per 24 hr
- Too-fast correction: cerebral edema
- Limit: lower Na⁺ ≤ 10–12 mEq/L/24 hr
Hyponatremia (<135)
- Hypotonic: water shifts INTO cells
- SIADH, HF dilution
- Thiazides, psychogenic polydipsia
Hypernatremia (>145)
- Hypertonic: water shifts OUT of cells
- Diabetes insipidus, dehydration
- Hypertonic IV fluids, impaired thirst
Hyponatremia (<135)
- Confusion, lethargy
- Muscle cramps, hyporeflexia
- Headache, nausea (cells swell)
Hypernatremia (>145)
- ★Twitching, hyperreflexia, spasticity
- Restlessness, irritability (cells shrink)
- Confusion, lethargy
- Thirst, dry sticky mucosa
Hyponatremia (<135)
- Serum Na⁺ < 135 mEq/L
- Serum osmolality < 275
Hypernatremia (>145)
- Serum Na⁺ > 145 mEq/L
- ↑ urine specific gravity (except DI)
Hyponatremia (<135)
- Seizure precautions
- Frequent neuro checks
- Serum Na⁺ q2–4h during correction
- Fluid restriction, strict I&O
Hypernatremia (>145)
- Seizure precautions
- Offer free water, daily weight
- Serum Na⁺ q2–4h during correction
- Frequent neuro checks
Hyponatremia (<135)
- ★Severe/seizures: 3% saline via pump
- Mild: fluid restriction
Hypernatremia (>145)
- Replace free water: D5W or 0.45% NS
- ★Desmopressin for diabetes insipidus
Hyponatremia (<135)
- Follow fluid restriction
- Avoid excess water intake
- Report headache, confusion, nausea
Hypernatremia (>145)
- Drink adequate water
- Don't ignore thirst
- Report restlessness, dry mouth
Hyponatremia (<135)
- ★Seizures from cerebral edema
- ↓ LOC progressing to coma
Hypernatremia (>145)
- Seizures if Na⁺ > 160
- ↓ LOC progressing to coma
Hyponatremia (<135)
- Too-fast correction: ODS (CPM)
- Limit: raise Na⁺ ≤ 8 mEq/L per 24 hr
Hypernatremia (>145)
- Too-fast correction: cerebral edema
- Limit: lower Na⁺ ≤ 10–12 mEq/L/24 hr
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Low sodium, swollen brain, seizures; high sodium, shrunken brain, agitation — correct either one slowly.
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Go further
- Commonly confusedHyponatremia vs HypernatremiaLow vs high sodium — opposite neuro signs and opposite correction, easy to reverse under pressure.
- SimulatorFluid & Electrolyte SimulatorChange one lab. Watch the whole patient respond. Sodium, potassium, calcium, magnesium, pH and volume, all linked — with a live ECG and an IV pole where every bag runs.
- TopicHypernatremiaThe 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.
- TopicHyponatremiaA confused postoperative patient with a sodium of 128 mEq/L doesn't need more fluids — they likely need less. Correcting hyponatremia too fast can be more dangerous than the…