What is the initial approach to treating hyponatraemia?

Initial Approach to Treating Hyponatremia

The initial approach to treating hyponatremia depends on symptom severity and volume status: for severe symptoms (seizures, coma, altered mental status), immediately administer 3% hypertonic saline as 100-150 mL boluses over 10 minutes, repeatable up to three times, targeting a 6 mmol/L increase over 6 hours; for asymptomatic or mildly symptomatic patients, determine volume status (hypovolemic, euvolemic, or hypervolemic) through physical examination and urine studies to guide specific therapy. 1, 2

Immediate Assessment

Determine Symptom Severity First

• Severe symptoms requiring emergent treatment include seizures, coma, somnolence, obtundation, cardiorespiratory distress, or acute mental status changes 1, 3
• Mild symptoms include nausea, vomiting, headache, weakness, or confusion without life-threatening manifestations 1, 4
• Asymptomatic patients have no clinical manifestations despite low sodium 1

Classify by Timing

• Acute hyponatremia (<48 hours duration) carries higher risk of cerebral edema and requires more aggressive initial correction 5, 2
• Chronic hyponatremia (>48 hours or unknown duration) requires slower, more cautious correction to prevent osmotic demyelination syndrome 1, 5

Treatment Algorithm Based on Symptom Severity

For Severe Symptomatic Hyponatremia (Medical Emergency)

Administer 3% hypertonic saline immediately as 100-150 mL IV boluses over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms resolve 1, 6, 2

• Target correction: Increase sodium by 4-6 mmol/L over the first 1-2 hours or until severe symptoms abate 1, 3
• Maximum correction limit: Do not exceed 8 mmol/L increase in 24 hours to prevent osmotic demyelination syndrome 1, 3, 6
• Monitor sodium levels every 2 hours during initial correction 1
• ICU admission is recommended for close monitoring during active treatment 1

For Asymptomatic or Mildly Symptomatic Hyponatremia

Assess volume status through physical examination looking for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemia), or jugular venous distention, peripheral edema, ascites (hypervolemia) 1, 4

Obtain initial laboratory workup:

• Serum osmolality and urine osmolality 1, 4
• Urine sodium concentration 1, 4
• Serum creatinine, BUN, glucose 1
• Thyroid function tests and cortisol if clinically indicated 1

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion 1, 4

• Urine sodium <30 mmol/L suggests hypovolemic state with 71-100% positive predictive value for response to saline 1
• Correct at a rate not exceeding 8 mmol/L in 24 hours 1, 4
• Once euvolemic, reassess and adjust therapy based on sodium response 1

Euvolemic Hyponatremia (SIADH)

Implement fluid restriction to 1 L/day as first-line treatment 1, 6, 2

• Diagnostic criteria include: urine osmolality >100 mOsm/kg, urine sodium >20-40 mmol/L, normal thyroid and adrenal function, absence of volume depletion or edema 1, 5
• If no response to fluid restriction after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1
• Second-line options for refractory cases: oral urea (40 g/day) or vasopressin receptor antagonists (tolvaptan 15 mg daily, titrated to 30-60 mg) 1, 6
• Avoid fluid restriction in neurosurgical patients with cerebral salt wasting, as this worsens outcomes 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 6

• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• For cirrhotic patients: Consider albumin infusion (6-8 g per liter of ascites drained if performing paracentesis) 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens fluid overload 1
• Sodium restriction (2-2.5 g/day) is more effective than fluid restriction alone for weight loss in cirrhosis 1

Critical Safety Considerations

Preventing Osmotic Demyelination Syndrome

Never exceed 8 mmol/L correction in 24 hours for most patients 1, 3, 6

• High-risk patients (advanced liver disease, alcoholism, malnutrition, severe hyponatremia <120 mmol/L) require even slower correction at 4-6 mmol/L per day 1
• If overcorrection occurs, immediately discontinue current fluids, switch to D5W (5% dextrose in water), and consider desmopressin to relower sodium 1
• Monitor for osmotic demyelination symptoms (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Common Pitfalls to Avoid

• Do not use fluid restriction in cerebral salt wasting (common in neurosurgical patients), as this requires volume and sodium replacement, not restriction 1
• Do not ignore mild hyponatremia (130-135 mmol/L), as it increases fall risk (21% vs 5% in normonatremic patients) and mortality 1
• Do not administer hypotonic fluids to hyponatremic patients, as this worsens the condition 1
• Avoid normal saline in SIADH, as it may paradoxically worsen hyponatremia; use hypertonic saline for severe symptoms or fluid restriction for mild cases 1

Monitoring Requirements

• During active correction: Check sodium every 2 hours initially for severe symptoms, then every 4 hours after symptom resolution 1
• After initial stabilization: Daily sodium monitoring until stable 1
• Calculate sodium deficit using formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1

Special Population Considerations

Cirrhotic Patients

• Hyponatremia <130 mmol/L increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• Tolvaptan carries higher risk of gastrointestinal bleeding in cirrhosis (10% vs 2% placebo) 1, 7
• More cautious correction rates (4-6 mmol/L per day) are mandatory 1

Neurosurgical Patients

• Distinguish between SIADH and cerebral salt wasting through volume status assessment 1
• Cerebral salt wasting requires volume expansion with isotonic or hypertonic saline plus fludrocortisone, not fluid restriction 1
• Avoid fluid restriction in subarachnoid hemorrhage patients at risk for vasospasm 1