What is the initial approach to treating hyponatremia (low sodium levels)?

Initial Approach to Treating Hyponatremia

The initial approach to hyponatremia depends on symptom severity and volume status: severely symptomatic patients require immediate 3% hypertonic saline to increase sodium by 4-6 mmol/L over 6 hours, while asymptomatic or mildly symptomatic patients should be managed based on volume status with fluid restriction for euvolemic/hypervolemic cases and isotonic saline for hypovolemic cases, always limiting total correction to 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1

Immediate Assessment

Determine symptom severity first, as this dictates urgency of treatment 1:

• Severe symptoms (seizures, coma, confusion, cardiorespiratory distress) require emergency treatment 1, 2
• Mild symptoms (nausea, vomiting, headache) allow for more measured approach 1
• Asymptomatic patients can be managed more conservatively 1

Assess volume status to guide specific therapy 1:

• Hypovolemic: signs of dehydration, orthostatic hypotension, dry mucous membranes 1
• Euvolemic: no edema, normal blood pressure, normal skin turgor 1
• Hypervolemic: edema, ascites, jugular venous distention 1

Obtain essential laboratory tests 1:

• Serum and urine osmolality 1
• Urine sodium concentration 1
• Urine electrolytes 1
• Serum uric acid 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

Administer 3% hypertonic saline immediately 1, 2:

• Give 100-150 mL bolus over 10 minutes 3, 4
• Can repeat up to three times at 10-minute intervals until symptoms improve 3
• Goal: increase sodium by 4-6 mmol/L over first 6 hours or until severe symptoms resolve 1, 2
• A 250 mL bolus is more effective than 100 mL (52% vs 32% achieving ≥5 mmol/L rise within 4 hours) without increasing overcorrection risk 3

Critical safety limit: never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 2, 4

Monitor sodium levels every 2 hours during initial correction 1

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends on volume status 1:

Hypovolemic Hyponatremia

Discontinue diuretics immediately 1

Administer isotonic saline (0.9% NaCl) for volume repletion 1:

• Urinary sodium <30 mmol/L predicts 71-100% response to saline infusion 1
• Continue until euvolemia achieved 1
• Still maintain 8 mmol/L per 24-hour correction limit 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is first-line treatment 1, 2, 4:

• Implement immediately for mild/asymptomatic cases 1
• Approximately 50% of SIADH patients do not respond to fluid restriction alone 4

If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1

Second-line options for resistant cases 1, 4:

• Oral urea (effective and safe) 4
• Tolvaptan 15 mg once daily, can titrate to 30-60 mg 1, 5
• Demeclocycline or lithium (less commonly used due to side effects) 1

Hypervolemic Hyponatremia (Cirrhosis, Heart Failure)

Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 2:

• Sodium restriction (not fluid restriction) is what drives weight loss, as fluid follows sodium 1
• Consider albumin infusion in cirrhotic patients 1

Avoid hypertonic saline unless life-threatening symptoms present, as it worsens edema and ascites 1

Critical Safety Considerations

High-risk patients require more cautious correction (4-6 mmol/L per day) 1:

• Advanced liver disease 1
• Alcoholism 1
• Malnutrition 1
• Prior encephalopathy 1

If overcorrection occurs 1:

• Immediately discontinue current fluids 1
• Switch to D5W (5% dextrose in water) 1
• Consider desmopressin to slow sodium rise 1

Watch for osmotic demyelination syndrome (typically 2-7 days after rapid correction) 1:

• Dysarthria 1
• Dysphagia 1
• Oculomotor dysfunction 1
• Quadriparesis 1

Common Pitfalls to Avoid

Never use fluid restriction in cerebral salt wasting (common in neurosurgical patients), as this worsens outcomes 1

Distinguish SIADH from cerebral salt wasting in neurosurgical patients, as treatments are opposite: SIADH requires fluid restriction while CSW requires volume and sodium replacement 1

Do not ignore mild hyponatremia (130-135 mmol/L), as even mild chronic hyponatremia increases fall risk (21% vs 5% in normonatremic patients) and is associated with cognitive impairment 2

Inadequate monitoring during active correction is a major pitfall 1

Normal saline may worsen hyponatremia in SIADH but is appropriate for hypovolemic states 1