Hypernatremia (serum sodium >145 mEq/L) reflects a relative deficit of free water rather than sodium excess, and is associated with higher mortality than any other electrolyte abnormality. [1-3] It occurs in 1–2% of ED presentations and up to 10% in ICU settings. [1][4] The most common cause is inadequate free water intake (impaired thirst, restricted access) with or without excess water losses. [1-2]
1. History
- Fluid intake: Quantify oral intake over the preceding days; ask about access to water, ability to self-hydrate, and thirst perception
- Fluid losses: Diarrhea, vomiting, excessive sweating, polyuria, fever, burns [1]
- Onset and duration: Acute (<48 hours) vs. chronic — critical for guiding correction rate [5]
- Urine output: High-volume dilute urine suggests diabetes insipidus; oliguria suggests dehydration [1]
- Medications: Diuretics, lithium, lactulose, sodium bicarbonate infusions, hypertonic saline [1][5]
- Iatrogenic factors: Recent IV fluids (especially NS or hypertonic solutions), tube feeds, sedation, intubation, restraints [1][6]
- Functional status: Cognitive impairment, immobility, nursing home residence, dependence on others for hydration [1][7]
2. Alarm Features
- Seizures, coma, or rapidly declining mental status — suggest severe hypernatremia (typically Na >160 mEq/L in adults) [1][5]
- Acute onset (<48 hours) with Na >160 mEq/L — risk of cerebral hemorrhage from vascular rupture due to brain shrinkage [5]
- Infants with hypernatremia — high risk of cerebral venous thrombosis, intracranial hemorrhage, and osmotic demyelination [8]
- Hemodynamic instability — orthostatic hypotension, tachycardia indicating severe hypovolemia [5]
- Hyperpnea (especially in infants) [5]
- Rapid correction of chronic hypernatremia — risk of cerebral edema, particularly in pediatric patients [9]
3. Medications
Causative medications
- Loop diuretics (furosemide) — increase free water loss [1][5]
- Osmotic diuretics (mannitol) — osmotic diuresis
- Lithium — causes nephrogenic diabetes insipidus [5]
- Lactulose — osmotic diarrhea [5]
- Hypertonic saline, sodium bicarbonate — iatrogenic sodium loading [1]
- Demeclocycline, amphotericin B, foscarnet — nephrogenic DI
Treatment fluids
- D5W (preferred IV option for free water replacement) [1][5]
- 0.45% NaCl (half-normal saline) or 0.2% NaCl (quarter-normal saline) [5]
- Oral/enteral free water — preferred route whenever possible [1]
- Desmopressin (DDAVP) — for central diabetes insipidus [1][10]
Avoid: Isotonic saline (0.9% NaCl) can worsen hypernatremia [1]
4. Diet
- Acute management: Oral free water is the preferred route for correction when the patient can drink safely [1][5]
- Tube feeds: Concentrated formulas without adequate free water flushes are a common cause of hospital-acquired hypernatremia; ensure adequate free water boluses with enteral nutrition
- Long-term: Ensure adequate daily fluid intake, especially in elderly or cognitively impaired patients; educate caregivers on hydration needs [7]
- Salt restriction if sodium overload is the etiology
5. Review of Systems
- Neurologic: Lethargy, confusion, weakness, irritability, restlessness, seizures, coma [1][5]
- GI: Nausea, vomiting, diarrhea (both as cause and symptom)
- Urinary: Polyuria/polydipsia (diabetes insipidus), oliguria (dehydration) [1]
- Constitutional: Fatigue, weight loss, fever [1]
- Musculoskeletal: Muscle weakness, cramps [5]
- Skin: Dry mucous membranes, decreased skin turgor
6. Collateral History and Family History
- Collateral from caregivers: Essential in elderly, cognitively impaired, or pediatric patients — ask about fluid provision, recent illness, falls preventing access to water [1][7]
- Nursing home/facility records: Fluid intake documentation, recent medication changes
- Family history: Hereditary nephrogenic diabetes insipidus (X-linked or autosomal recessive), familial central DI
- Social context: Living alone, social isolation, elder neglect, psychiatric illness (depression causing hypodipsia) [1]
7. Risk Factors
- Extremes of age (infants and elderly) [1][5]
- Altered mental status — sedation, intubation, dementia, delirium [6]
- Nursing home residence or dependence on others for hydration [7]
- ICU admission — prevalence up to 10% [4]
- Cognitive or physical disability limiting water access [1]
- Diabetes insipidus (central or nephrogenic) [1]
- Febrile illness — insensible losses [5]
- Osmotic diuresis — hyperglycemia, mannitol, urea [5]
- Chronic kidney disease — impaired concentrating ability
8. Differential Diagnosis
- Dehydration from inadequate intake — most common cause; clinical history usually diagnostic [1]
- Diabetes insipidus (central vs. nephrogenic) — polyuria with dilute urine despite dehydration; distinguish with water deprivation test and desmopressin challenge [1]
- Osmotic diuresis — hyperglycemia (DKA/HHS), mannitol, urea; check glucose and calculate corrected sodium
- GI losses — diarrhea (especially osmotic), vomiting [1]
- Iatrogenic sodium loading — hypertonic saline, sodium bicarbonate, hypertonic dialysis [1]
- Salt poisoning — rare, high mortality; history of excessive salt ingestion [1][11]
- Primary hyperaldosteronism / Cushing syndrome — rare causes of mild hypernatremia with sodium retention
- Adipsic (essential) hypernatremia — hypothalamic lesion destroying osmoreceptors; absent thirst despite hyperosmolality
9. Past Medical History
- Prior episodes of hypernatremia or dehydration
- Diabetes insipidus — prior neurosurgery, pituitary pathology, head trauma (central DI); lithium use, renal disease (nephrogenic DI)
- Dementia, stroke, psychiatric illness — impaired thirst or self-care
- Diabetes mellitus — osmotic diuresis risk
- Chronic kidney disease — impaired urinary concentrating ability
- Prior neurosurgery or TBI — risk for central DI
- Medications — complete medication reconciliation
10. Physical Exam
- Vitals: Tachycardia, orthostatic hypotension (hypovolemia); fever (both cause and consequence) [5]
- Neurologic: Level of consciousness (lethargy → obtundation → coma correlates with severity); muscle tone, reflexes, tremor, myoclonus [5]
- Mucous membranes: Dry, furrowed tongue
- Skin: Decreased turgor (tenting), doughy skin texture in hypernatremic dehydration
- Fontanelle (infants): Sunken (dehydration) or bulging (if cerebral edema from overcorrection) [9]
- Weight: Compare to recent baseline if available — acute weight loss suggests fluid deficit
11. Lab Studies
- Serum sodium — confirms diagnosis (>145 mEq/L); severity grading: mild (146–150), moderate (151–159), severe (≥160) [1]
- Serum osmolality — invariably elevated; confirms hyperosmolality
- BMP/CMP — potassium, glucose, BUN, creatinine (assess renal function, identify osmotic diuresis)
- Urine osmolality and urine sodium — key to determining etiology:
- Urine osm >800 mOsm/kg → appropriate renal response (extrarenal losses or inadequate intake)
- Urine osm <300 mOsm/kg → diabetes insipidus [1]
- Urine osm 300–800 → partial DI or osmotic diuresis
- Urine specific gravity — <1.005 with dehydration suggests DI [1]
- Serum calcium — hypercalcemia causes nephrogenic DI [5]
- Glucose — correct sodium for hyperglycemia (add 1.6 mEq/L per 100 mg/dL glucose above 100) [1]
12. Imaging
- Not routinely required for uncomplicated hypernatremia
- Brain MRI — indicated if:
- Suspicion for central diabetes insipidus (pituitary/hypothalamic pathology) [1]
- Neurologic deficits disproportionate to sodium level (evaluate for cerebral hemorrhage, venous thrombosis, osmotic demyelination) [8]
- Failure to respond to treatment
- CT head — in acute setting if concern for intracranial hemorrhage (brain shrinkage can cause bridging vein rupture and subarachnoid hemorrhage) [5]
13. Special Tests
- Free Water Deficit Calculator
$$\text{FWD (L)} = \text{TBW} \times \left(\frac{\text{Serum Na}}{140} - 1\right)$$
where TBW = 0.6 × weight (kg) for adult males, 0.5 for adult females, 0.45–0.5 for elderly [1]
- Water deprivation test — for suspected diabetes insipidus; continued dilute urine output despite dehydration confirms DI [1]
- Desmopressin (DDAVP) challenge — distinguishes central DI (urine concentrates with DDAVP) from nephrogenic DI (no response) [1]
- Copeptin levels — emerging biomarker for DI diagnosis as an alternative to water deprivation testing
14. ECG
- Not a primary diagnostic tool for hypernatremia, but obtain if:
- Concurrent electrolyte abnormalities (hypokalemia, hypercalcemia)
- Hemodynamic instability or tachycardia
- No pathognomonic ECG findings for hypernatremia itself
- Monitor for hypokalemia-related changes (U waves, QT prolongation) as potassium shifts may occur during correction
15. Assessment
Severity classification
- Mild: Na 146–150 mEq/L — often asymptomatic or nonspecific fatigue/weakness [1]
- Moderate: Na 151–159 mEq/L — lethargy, confusion, nausea
- Severe: Na ≥160 mEq/L — obtundation, seizures, coma; mortality increases significantly [3][5]
Chronicity matters: Acute (<48 hours) hypernatremia carries risk of cerebral hemorrhage from brain shrinkage but can be corrected rapidly. Chronic (>48 hours or unknown duration) hypernatremia has adapted brain osmolytes, and overly rapid correction risks cerebral edema. [5][9]
Complications: Cerebral hemorrhage (subarachnoid, subdural), cerebral venous thrombosis, osmotic demyelination syndrome, rhabdomyolysis, acute kidney injury. [5][8][10][12]
The following figure illustrates the consequences of rapid changes in plasma sodium concentration, including the risk of osmotic demyelination with rapid sodium increases and cerebral edema with rapid correction of chronic hypernatremia:
16. Treatment Plan
Step 1 — Address the underlying cause [5]
- Stop offending medications (diuretics, lactulose, lithium)
- Control fever, hyperglycemia, GI losses
- Treat diabetes insipidus with desmopressin (central DI) or remove offending agent (nephrogenic DI)
Step 2 — Calculate free water deficit and plan replacement [1]
Step 3 — Fluid replacement
- Preferred route: Oral or enteral free water [1][5]
- IV options: D5W (most hypotonic), 0.2% NaCl, 0.45% NaCl [5]
- Avoid isotonic saline (0.9% NaCl) — can worsen hypernatremia [1]
- Account for ongoing losses (insensible, urinary, GI) in addition to calculated deficit [5]
Step 4 — Correction rate
- Acute hypernatremia (<48 hours): Can correct at 1 mEq/L/hour safely [5][11]
- Chronic or unknown duration: Traditional recommendation is ≤10 mEq/L per 24 hours; more recent evidence supports up to 12 mEq/L per 24 hours in adults [1][5][7]
- Emerging data: A large cohort study found faster correction (>0.5 mmol/L/h) was associated with improved survival and no neurological complications in adults with severe hypernatremia. A 2025 meta-analysis confirmed that faster correction appears safe and may benefit patients with severe admission-related hypernatremia, particularly within the first 24 hours, with no major neurological complications when correction rate was <1 mmol/L/h. [3][13]
- Infants: Correct at <0.5 mEq/L/hour (<12 mEq/L per 24 hours) due to higher risk of cerebral edema [1][9]
Step 5 — Monitor serum sodium every 4–6 hours during active correction to ensure target rate is achieved and adjust fluids accordingly [6-7]
17. Disposition
Admit if
- Na ≥155–160 mEq/L or any neurologic symptoms (confusion, lethargy, seizures)
- Hemodynamic instability or significant volume depletion
- Unable to tolerate oral fluids or requires IV correction
- Unclear etiology requiring workup (e.g., suspected DI)
- Underlying condition requiring inpatient management
ICU admission if
- Na ≥160 mEq/L with altered mental status or seizures
- Hemodynamic instability requiring vasopressors or aggressive resuscitation
- Need for frequent (q2–4h) sodium monitoring
Observation may be appropriate for
Discharge if
- Mild hypernatremia with clear cause (e.g., inadequate intake), correctable at home with oral hydration
- Sodium trending toward normal, patient tolerating PO, and reliable follow-up ensured
Consult nephrology or endocrinology for
- Suspected diabetes insipidus
- Refractory hypernatremia despite appropriate fluid replacement
- Severe hypernatremia (Na ≥160) or uncertain etiology
18. Follow Up / Return Precautions
- Recheck sodium within 24–48 hours after discharge for mild cases managed outpatient
- PCP follow-up within 1–3 days for patients discharged from the ED
- Return precautions: Instruct patients/caregivers to return for worsening confusion, lethargy, seizures, inability to drink, persistent vomiting/diarrhea, or decreased urine output
- Caregiver education: Ensure adequate daily fluid intake, especially for elderly or cognitively impaired patients; set hydration schedules if needed [7]
- Medication review: Reassess diuretics, lithium, and other contributing medications at follow-up
- Expected course: Mild hypernatremia typically corrects within 24–48 hours with adequate oral hydration; severe cases may require several days of monitored correction [1][5]
- Long-term: Patients with diabetes insipidus require endocrinology follow-up and ongoing desmopressin management; patients with recurrent hypernatremia need evaluation for underlying thirst impairment or access issues [1]
References
1. Diagnosis and Management of Sodium Disorders: Hyponatremia and Hypernatremia. — Miller NE, Rushlow D, Stacey SK. American Family Physician. 2023.
2. Pathophysiology and Aetiologies of Hypernatremia. — Drummond JB, Freitas LGO, Freitas IS, Romanowski RM, Soares BS. Best Practice & Research. Clinical Endocrinology & Metabolism. 2025.
3. Rate of Correction and All-Cause Mortality in Patients With Severe Hypernatremia. — Feigin E, Feigin L, Ingbir M, Ben-Bassat OK, Shepshelovich D. JAMA Network Open. 2023.
4. Diagnosis and Treatment of Hypernatremia. — Tomkins M, Mc Donald D, Green D, O'Reilly MW, Sherlock M. Best Practice & Research. Clinical Endocrinology & Metabolism. 2025.
5. Hypernatremia. — Adrogué HJ, Madias NE. The New England Journal of Medicine. 2000.
6. Hypernatremic Disorders in the Intensive Care Unit. — Arora SK. Journal of Intensive Care Medicine. 2011.
7. Approach to the Management of Hypernatraemia in Older Hospitalised Patients. — Brennan M, Mulkerrin L, O'Keeffe ST, O'Shea PM. The Journal of Nutrition, Health & Aging. 2021.
8. Neuroimaging Spectrum of Severe Hypernatremia in Infants With Neurological Manifestations. — Vyas S, Saini AG, Kaur A, et al. Neuropediatrics. 2021.
9. Disorders of Plasma Sodium — Causes, Consequences, and Correction. — Sterns RH. The New England Journal of Medicine. 2015.
10. Rapid-Onset Hypernatremia Induced by Central Diabetes Insipidus Leading to Osmotic Demyelination Syndrome: A Case Report. — Zhang Y, Chen R, Kong X, Yan Y, Su S. Frontiers in Medicine. 2024.
11. Treatment of Acute Hypernatremia Caused by Sodium Overload in Adults: A Systematic Review. — Goshima T, Terasawa T, Iwata M, et al. Medicine. 2022.
12. Non-Hyponatremia-Associated Osmotic Demyelination Syndrome: An Analysis of Published Cases. — Ravioli S, Fussi F, Schwarz C, Lindner G. The American Journal of Medicine. 2026.
13. Systematic Review and Meta-Analysis of the Treatment of Hypernatremia in Adult Hospitalized Patients: Impact on Mortality, Morbidity, and Treatment-Related Side Effects. — Kitisin N, Raykateeraroj N, Hikasa Y, et al. Journal of Critical Care. 2025.