Hypernatraemia 🧂
Clinical guide for managing hypernatraemia. Free water deficit calculator, causes, treatment protocols, and correction rates for on-call doctors.
🧠 Definition & Pathophysiology
- Hypernatraemia = Serum Na⁺ > 145 mmol/L
- Usually due to water deficit relative to sodium (dehydration > sodium gain)
- Common causes: fluid losses (GI, renal, skin), DI, osmotic diuresis, inadequate intake
📋 Clinical Features
- Often asymptomatic until severe (> 160 mmol/L)
- Signs of dehydration: dry mucous membranes, decreased skin turgor
- Lethargy, weakness, irritability, confusion
- Seizures, coma in severe or rapidly developing cases
🧪 Investigations
- Serum Na⁺, K⁺, U&E, glucose, calcium
- Urine sodium and osmolality to assess renal handling
- Consider serum osmolality
- Assess volume status clinically
📈 Classification
- Assess based on volume status:
- Hypovolaemic: e.g. GI losses, diuretics, renal losses
- Euvolaemic: e.g. Diabetes Insipidus (central/nephrogenic)
- Hypervolaemic: e.g. excess Na⁺ intake (iatrogenic), mineralocorticoid excess
💊 Management
- Treat underlying cause
- Correct dehydration gradually over days to avoid cerebral oedema
- Use oral or IV hypotonic fluids (e.g. 5% dextrose)
- In DI, consider DDAVP (desmopressin)
- Target Na⁺ reduction: no more than 10-12 mmol/L in 24h
⚠️ Monitoring
- Monitor serum sodium 4–6 hourly during correction
- Strict fluid balance
- Watch for signs of cerebral oedema or fluid overload
Free Water Deficit Calculator
Estimate free water deficit in hypernatraemia
Formula
Free Water Deficit = TBW × ((Na – 140) / Na)
TBW = total body water fraction × weight (kg)
External resources
Note Template
Ready-to-use clinical note structure
🕒 16 / 10 / 2026 — 16:25 ATRP re: hypernatraemia Patient: [age] [sex] Admission Dx: [reason for admission] PMHx: [diabetes, renal disease, diuretics, impaired thirst] 🧾 Hx: • Symptoms: [confusion, lethargy, weakness, seizures] • Duration: [acute/chronic] • Fluid intake: [oral / IV / impaired access] • Fluid losses: [diarrhoea, vomiting, polyuria, fever] • Medications: [diuretics, lithium, others] 🩺 Exam: • HR: __ BP: __ Temp: __ RR: __ SpO₂: __ • Volume status: [hypovolaemic / euvolaemic / hypervolaemic] • Neuro: [alert / drowsy / confused / seizures] 📋 Impression: Likely cause: [dehydration / DI / iatrogenic / other] 📌 Plan: • U&E, glucose, osmolality (serum + urine) • Regularly assess volume status • Calculate free water deficit - estimated at [weight] kg: [calculated deficit] • Rehydrate carefully: avoid rapid correction - Dex 5% at 100ml/hr • Monitor Na⁺ closely (target ↓ <10 mmol/L per 24hr) • Treat underlying cause 👤 [Your Name], [Role] IMC: _______
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