RFT – Sodium

ABCs

• Check vitals
• Assess:
  • Neurological status
  • Volume status
• Always:
  • Confirm sodium
  • Compare with previous levels
  • Correct sodium if hyperglycemia is present:
    • or every ↑ glucose by 5.6 mmol/L → Na ↓ ~1.6 mmol/L

Hyponatremia

• Features
  • Mild: Fatigue, weakness, nausea
  • Moderate: Confusion, ataxia
  • Severe: Seizures, coma
• Investigations
  • Serum osmolality
    • <275 mOsm/kg → true hypotonic hyponatremia
  • Urine Osm <100 mOsm/kg → Excess water intake (e.g., polydipsia)
  • Urine Osm >100 mOsm/kg → ADH active → proceed to urine Na
  • Urine Na <30 mmol/L → Hypovolemia (GI losses, dehydration)
  • Urine Na >30 mmol/L → SIADH, renal loss, endocrine causes
• Determine:
  • Acute vs chronic
  • Volume status

Volume Status	Treatment
Hypovolemic	IV Normal Saline (0.9%)
Euvolemic	Fluid restriction (500–1000 mL/day)
Hypervolemic	Fluid restriction ± loop diuretics

• When to use Hypertonic Saline (3%)
  • Acute symptomatic hyponatremia
  • Neurological symptoms (seizures, coma)
  • Bolus: 100 mL over 10 min (repeat ×3)
    • Alternative: 150 mL over 20 min (repeat ×2)
• Do NOT start alone → call a senior first
• Monitor Na hourly during correction
• Avoid rapid correction → risk of osmotic demyelination

Hypernatremia

• Features
  • Confusion, altered mental status
  • Weakness, fatigue
  • Nausea, vomiting
• Management
  • Replace free water
  • Oral / NGT if possible
  • Most cases → D5W
  • Hypovolemic → 0.45% NS → then D5W
• Key Points
  • Correct slowly
  • Avoid rapid shifts → risk of cerebral edema
  • Always consult a senior before initiating a correction

Monitoring & handover

• Check: Sodium + RFT every 4–6 hours
• Ensure: Clear handover
• Ongoing plan documented

related · altered mental status · seizures · hyperglycemia · acute kidney injury

Studying for R1? The IM Rapid Review covers this in the same format — see the sample chapter.

Last reviewed · May 2026