Chart — Electrolytes
Sodium Disorder Comparison Chart
Side-by-side comparison of hyponatremia and hypernatremia — causes, neurological effects, fluid status, IV fluid selection, correction rate considerations, and nursing priorities.
Educational use only. Sodium disorder management requires provider orders, careful rate calculations, and continuous neurological monitoring. Rapid correction of either disorder can cause permanent neurological injury. Always follow institutional protocols. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
Hyponatremia vs Hypernatremia — At a Glance
| Hyponatremia | Hypernatremia | |
|---|---|---|
| Definition | Na⁺ < 136 mEq/L | Na⁺ > 145 mEq/L |
| Osmolality | Serum osmolality low (< 275 mOsm/kg) | Serum osmolality high (> 295 mOsm/kg) |
| Brain Effect | Water moves INTO brain cells → cerebral edema → neurological depression | Water moves OUT of brain cells → brain shrinks → vessel tearing/hemorrhage risk |
Causes
| Fluid Status | Hyponatremia Causes | Hypernatremia Causes |
|---|---|---|
| Hypovolemic | Vomiting, diarrhea, diuretics (thiazides), sweating, adrenal insufficiency | Fever/sweating, inadequate water intake, diarrhea (infants), diabetes insipidus |
| Euvolemic | SIADH (most common) — inappropriate ADH secretion retains excess free water; hypothyroidism, psychogenic polydipsia | Diabetes insipidus (central or nephrogenic) — large volumes of dilute urine without water replacement |
| Hypervolemic | Heart failure, cirrhosis, nephrotic syndrome — water excess dilutes sodium | Hypertonic saline infusion, excessive sodium bicarbonate, hypertonic tube feeds |
Symptoms by Severity
| Severity | Hyponatremia Symptoms | Hypernatremia Symptoms |
|---|---|---|
| Mild | Often asymptomatic; mild headache, nausea, fatigue | Intense thirst, dry mucous membranes, decreased urine output (unless DI) |
| Moderate | Nausea, vomiting, headache, muscle cramps, disorientation, personality change | Restlessness, agitation, irritability, muscle weakness, decreased skin turgor |
| Severe | Seizures, respiratory arrest, coma — brain swelling compresses vital structures | Seizures, coma, intracranial hemorrhage — bridging veins tear as brain shrinks from skull |
Treatment and Nursing Considerations
| Hyponatremia | Hypernatremia | |
|---|---|---|
| Fluid Approach | Euvolemic/hypervolemic: Fluid restriction Hypovolemic: Isotonic saline (0.9% NaCl) Severe/symptomatic: 3% hypertonic saline (ICU setting only) | Mild/moderate: Oral water (if conscious/safe) or D5W IV Hypovolemic: Isotonic saline first to restore volume, then hypotonic (0.45% NaCl) DI: DDAVP for central DI; address nephrogenic DI cause |
| Correction Rate | Maximum 8–10 mEq/L per 24 hours | Maximum 10 mEq/L per 24 hours |
| Rapid Correction Risk | Osmotic demyelination syndrome (ODS/CPM) — irreversible brainstem demyelination, permanent neurological deficits | Cerebral edema — rapid water entry into previously shrunken brain cells, fatal brain herniation |
| Monitoring | Na⁺ every 4–6 hours during correction; neurological assessment q1–2 hours; I&O; seizure precautions | Na⁺ every 4–6 hours during correction; neurological assessment; I&O; urine specific gravity; fall precautions |
| Key Nursing Action | Implement seizure precautions; restrict free water; document accurate I&O; notify provider of neurological changes | Ensure free water access; mouth care for dry mucosa; fall/seizure precautions; assess skin turgor and mucous membranes |
NCLEX Fast Facts
- SIADH = dilutional hyponatremia from excess ADH — treat with fluid restriction, not sodium replacement
- Diabetes insipidus = large volumes of dilute urine = hypernatremia — opposite of SIADH
- Both disorders require gradual correction — never correct a chronic sodium disorder rapidly
- Hyponatremia → brain swells (water INTO cells); Hypernatremia → brain shrinks (water OUT of cells)
- Critical Na⁺ values: < 120 (hyponatremia) and > 160 (hypernatremia) both require immediate notification
- For hyponatremia from SIADH: fluid restriction is first-line, not IV sodium — excess sodium without correcting the underlying free water excess is ineffective
- Hypertonic saline (3% NaCl) is only used for severe symptomatic hyponatremia with seizures or coma — requires ICU monitoring
Related Resources
Standards & sources
Fact-checked Jun 20, 2026This page is written to align with ANA / NANDA Clinical Standards. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →