When is hypertonic saline (3% sodium chloride) indicated and how should it be administered in a fluid‑overloaded patient with severe hyponatraemia or cerebral oedema?

Hypertonic Saline (3% NaCl) in Fluid‑Overloaded Patients with Severe Hyponatraemia

Hypertonic saline (3% NaCl) is indicated for severe symptomatic hyponatraemia even in fluid‑overloaded patients when life‑threatening neurological symptoms (seizures, coma, altered mental status) are present, but it must be avoided in hypervolaemic hyponatraemia without severe symptoms because it worsens ascites and oedema. 1

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When Hypertonic Saline Is Indicated in Fluid Overload

Severe Symptomatic Hyponatraemia (Life‑Threatening)

• Administer 3% hypertonic saline immediately when serum sodium is <120 mmol/L and the patient exhibits severe neurological symptoms such as seizures, coma, confusion, or altered mental status—even if clinical hypervolaemia (ascites, peripheral oedema, pulmonary congestion) is present. 1, 2
• The initial goal is to raise serum sodium by 6 mmol/L over 6 hours or until severe symptoms resolve, using bolus infusions of 100–150 mL of 3% NaCl repeated at 10‑minute intervals (up to three boluses). 1, 3, 4
• Total correction must not exceed 8 mmol/L in any 24‑hour period to prevent osmotic demyelination syndrome; high‑risk patients (cirrhosis, alcoholism, malnutrition) should be limited to 4–6 mmol/L per day. 1, 3

Dosing Protocol

• Bolus administration: Give 100 mL of 3% NaCl intravenously over 10 minutes; repeat up to three times at 10‑minute intervals if symptoms persist. 1, 4
• A 250 mL bolus is more effective than 100 mL (52% vs 32% achieving ≥5 mmol/L rise within 4 hours) and does not increase overcorrection risk, but it may worsen fluid overload in hypervolaemic patients. 4
• Monitor serum sodium every 2 hours during initial correction, then every 4–6 hours after symptom resolution. 1, 3

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When Hypertonic Saline Is Contraindicated in Fluid Overload

Hypervolaemic Hyponatraemia Without Severe Symptoms

• Avoid hypertonic saline in patients with cirrhosis, heart failure, or nephrotic syndrome who have hypervolaemic hyponatraemia (ascites, oedema, elevated jugular venous pressure) but no life‑threatening neurological symptoms, because it exacerbates fluid retention and worsens ascites. 1
• First‑line therapy for hypervolaemic hyponatraemia is fluid restriction to 1–1.5 L/day for serum sodium <125 mmol/L, combined with discontinuation of diuretics temporarily. 1
• In cirrhotic patients, albumin infusion (8 g per litre of ascites removed) alongside fluid restriction is preferred over hypertonic saline. 1

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Transition After Symptom Resolution

Discontinuing Hypertonic Saline

• Stop 3% NaCl when severe symptoms resolve (e.g., seizures cease, mental status normalizes) and transition to protocols for mild or asymptomatic hyponatraemia. 3
• Switch to isotonic maintenance fluids (0.9% NaCl) at 30 mL/kg/day for adults once clinical euvolaemia is achieved; avoid hypotonic solutions (0.45% saline, lactated Ringer's, D5W) which worsen hyponatraemia. 1, 3
• Implement fluid restriction to 1 L/day and monitor serum sodium every 4 hours instead of every 2 hours. 3

Correction Limits After Initial Bolus

• After the initial 6 mmol/L correction in 6 hours, limit further correction to only 2 mmol/L in the following 18 hours to stay within the 8 mmol/L/24‑hour ceiling. 3
• Continue treatment until sodium reaches 125–130 mmol/L, not the normal range; aiming for normonatraemia acutely increases overcorrection risk. 1, 3

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Monitoring and Safety

Intensive Monitoring Protocol

• Check serum sodium every 2 hours during the initial correction phase of severe symptomatic hyponatraemia. 1, 3
• Measure urine output frequently; an unwanted water diuresis (e.g., from resolving SIADH or cerebral salt wasting) can cause inadvertent overcorrection. 5
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically 2–7 days after rapid correction. 1

Managing Overcorrection

• If sodium rises >8 mmol/L in 24 hours, immediately stop hypertonic saline and administer 5% dextrose in water (D5W) or desmopressin to lower sodium levels back to safe limits. 1, 5
• Desmopressin can terminate an unwanted water diuresis and reverse overcorrection effectively. 5

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Special Populations

Cirrhotic Patients

• Correction rate must not exceed 4–6 mmol/L per day (maximum 8 mmol/L in 24 hours) due to exceptionally high risk of osmotic demyelination syndrome. 1
• Hypertonic saline worsens ascites and oedema in cirrhosis; reserve it only for life‑threatening symptoms (seizures, coma). 1
• Albumin infusion is preferred over hypertonic saline for non‑emergent correction in cirrhotic patients with hypervolaemic hyponatraemia. 1

Heart Failure Patients

• Diuretics should be continued at reduced doses even in the presence of mild hyponatraemia (126–135 mmol/L) if volume overload persists, because stopping diuretics prematurely worsens outcomes. 1
• Fluid restriction to 1–1.5 L/day is first‑line therapy for serum sodium <125 mmol/L in heart failure; hypertonic saline is reserved for severe symptomatic cases only. 1

Neurosurgical Patients (Cerebral Salt Wasting)

• Distinguish cerebral salt wasting (CSW) from SIADH by volume status: CSW presents with true hypovolaemia (orthostatic hypotension, dry mucous membranes, CVP <6 cm H₂O), while SIADH is euvolaemic. 1
• CSW requires aggressive volume and sodium replacement with isotonic or hypertonic saline (50–100 mL/kg/day); fluid restriction is contraindicated and worsens outcomes. 1
• In subarachnoid haemorrhage patients at risk of vasospasm, never use fluid restriction; consider fludrocortisone (0.1–0.2 mg daily) or hydrocortisone to prevent natriuresis. 1

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Common Pitfalls

• Using hypertonic saline in hypervolaemic hyponatraemia without life‑threatening symptoms worsens ascites and oedema; fluid restriction is first‑line therapy. 1
• Correcting chronic hyponatraemia faster than 8 mmol/L in 24 hours causes osmotic demyelination syndrome; high‑risk patients require even slower correction (4–6 mmol/L per day). 1, 3
• Failing to monitor serum sodium every 2 hours during initial correction risks inadvertent overcorrection from an unwanted water diuresis. 1, 5
• Misdiagnosing CSW as SIADH and applying fluid restriction in neurosurgical patients worsens hypovolaemia and increases cerebral ischaemia risk. 1
• Stopping diuretics prematurely in heart failure patients with mild hyponatraemia (126–135 mmol/L) leads to persistent congestion and poorer prognosis. 1