Hypernatraemia 🧂

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🧠 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

🔗 External Resources

    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)

    Note Template

    Ready-to-use clinical note structure

    🕒 20 / 11 / 2025 — 22:36

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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