Hypernatremia: workup and management
Serum sodium >145 mEq/L means a free water deficit, usually from impaired thirst or access to water combined with losses. Estimate the free water deficit, replace with hypotonic fluid at a controlled rate, and evaluate urine osmolality for diabetes insipidus or osmotic diuresis.
Working diagnosis
Adult · US guidelines
Draft · awaiting physician review
01Orient
What's new in the evidence
- Observational ICU data (2019) found no harm from faster correction of hypernatremia; most clinicians still limit chronic correction to about 10–12 mEq/L per day
- Arginine vasopressin deficiency and resistance are the new names for central and nephrogenic diabetes insipidus (2022 nomenclature)
Differential diagnoses
- Inadequate water intake (older adults, dementia, altered mental status)
- GI losses or insensible losses (fever, burns)
- Osmotic diuresis (hyperglycemia, urea, mannitol)
- Central diabetes insipidus (arginine vasopressin deficiency)
- Nephrogenic diabetes insipidus (lithium, hypercalcemia, hypokalemia)
- Hypertonic saline or sodium bicarbonate administration
02Assess
Risk scores and decision tools
- Free water deficit = total body water × (Na/140 − 1)
- Urine osmolality to separate renal from extrarenal water loss
- Desmopressin response to separate central from nephrogenic DI
Key history questions
- Access to water, thirst, intake
- Polyuria and nocturia
- Lithium, diuretics, recent hypertonic fluids
- Head injury, neurosurgery, pituitary disease
- Diarrhea, fever, burns
Examination findings
- Mental status: lethargy, confusion, seizures
- Volume status
- Neurological signs
03Investigate
Initial investigations
- BMP, glucose, calcium, potassium
- Serum and urine osmolality, urine sodium
- Accurate urine output
Advanced investigations
- Urine osmolality <300 mOsm/kg with polyuria suggests DI; trial of desmopressin separates central from nephrogenic
- MRI pituitary for central DI
04Treat
Immediate management
- Hypovolemic shock: isotonic saline first to restore perfusion
- Then replace the free water deficit with D5W or enteral water
First-line treatment
- Free water deficit = total body water × (Na ÷ 140 − 1); add ongoing losses
- Chronic hypernatremia (>48 h): aim for a fall of about 10 mEq/L or less per 24 hours
- Acute hypernatremia (<48 h): faster correction is reasonable
Second-line treatment
- Central DI: desmopressin with careful sodium monitoring
- Nephrogenic DI: treat the cause, thiazide, low-solute diet
Specialist referrals
- Endocrinology for DI
- Nephrology for complex cases
05Disposition
Admission criteria
- Sodium ≥155 mEq/L or neurological symptoms
- Unable to drink adequately
Safe discharge criteria
- Sodium improving and able to drink
- Cause addressed; access to water assured
Follow-up timing
- Repeat sodium within 2–3 days of discharge
Patient instructions
- Drink to thirst; carers to offer water regularly
Monitoring
- Sodium every 4–6 hours while correcting
- Urine output and weight
Clinical pearls and pitfalls
- Hypernatremia in hospital is often iatrogenic: watch free water intake in sick, intubated or confused patients
- Evidence for slow correction in adults is weaker than for hyponatremia, but most clinicians still limit chronic correction to about 10–12 mEq/L per day
RefGuidelines and landmark evidence
For education only. Typical adult starting points; confirm doses against renal function, allergies, interactions and your institution's protocols. Not a substitute for clinical judgment or senior review.