What is the initial approach to treating hyponatremia?

Initial Approach to Treating Hyponatremia

The initial approach to treating hyponatremia must be determined by symptom severity and volume status, with severe symptomatic hyponatremia requiring immediate 3% hypertonic saline to correct sodium by 6 mmol/L over 6 hours, while asymptomatic or mildly symptomatic cases require careful assessment of volume status (hypovolemic, euvolemic, or hypervolemic) to guide specific therapy. 1

Immediate Assessment: Symptom Severity

Determine if the patient has severe symptoms (seizures, coma, altered mental status, cardiorespiratory distress) versus mild symptoms (nausea, headache, weakness) versus asymptomatic hyponatremia. 1, 2

For Severe Symptomatic Hyponatremia (Medical Emergency)

• Administer 3% hypertonic saline immediately as 100-150 mL IV bolus over 10 minutes, which can be repeated up to three times at 10-minute intervals until symptoms improve. 1, 3
• Target correction of 6 mmol/L over the first 6 hours or until severe symptoms resolve. 1
• Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome. 1, 2
• Monitor serum sodium every 2 hours during initial correction phase. 1

Volume Status Assessment (For Non-Severe Cases)

After stabilizing any severe symptoms, assess extracellular fluid volume status through physical examination, though recognize this has limited accuracy (sensitivity 41%, specificity 80%). 1

Hypovolemic Hyponatremia

Look for: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins. 1

• Check urine sodium: <30 mmol/L suggests extrarenal losses (GI losses, burns, dehydration); >20 mmol/L suggests renal losses (diuretics). 1, 4
• Treatment: Discontinue diuretics and administer isotonic saline (0.9% NaCl) for volume repletion. 1
• Correction rate: Do not exceed 8 mmol/L in 24 hours. 1

Euvolemic Hyponatremia (SIADH)

Look for: No edema, no orthostatic hypotension, normal skin turgor, moist mucous membranes. 1

• Diagnostic criteria: Urine sodium >20-40 mmol/L with urine osmolality >300 mOsm/kg in a euvolemic patient. 1
• First-line treatment: Fluid restriction to 1 L/day. 1, 4
• If no response to fluid restriction: Add oral sodium chloride 100 mEq three times daily. 1
• Second-line options: Urea or vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrated to 30-60 mg). 1, 3

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Look for: Peripheral edema, ascites, jugular venous distention, pulmonary congestion. 1

• Treatment: Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L. 1, 4
• Discontinue diuretics temporarily if sodium <125 mmol/L. 1
• For cirrhotic patients: Consider albumin infusion alongside fluid restriction. 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens edema and ascites. 1

Initial Diagnostic Workup

Obtain the following tests immediately: 1

• Serum osmolality (to exclude pseudohyponatremia)
• Urine osmolality and urine sodium concentration
• Serum uric acid (<4 mg/dL suggests SIADH with 73-100% positive predictive value)
• Thyroid-stimulating hormone (to rule out hypothyroidism)
• Serum creatinine and electrolytes

Critical Safety Considerations

Correction Rate Limits

• Standard patients: Maximum 8 mmol/L in 24 hours. 1, 2
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): Maximum 4-6 mmol/L per day. 1
• Overly rapid correction causes osmotic demyelination syndrome, presenting 2-7 days later with dysarthria, dysphagia, oculomotor dysfunction, or quadriparesis. 1

Special Population: Neurosurgical Patients

Distinguish between SIADH and cerebral salt wasting (CSW) as treatments are opposite. 1

• CSW requires volume and sodium replacement (isotonic or hypertonic saline), NOT fluid restriction. 1
• CSW indicators: True hypovolemia with high urine sodium despite volume depletion, common in subarachnoid hemorrhage. 1
• Consider fludrocortisone for CSW in subarachnoid hemorrhage patients at risk of vasospasm. 1

Common Pitfalls to Avoid

• Never use fluid restriction in cerebral salt wasting - this worsens outcomes. 1
• Never ignore mild hyponatremia (130-135 mmol/L) - it increases fall risk (21% vs 5%) and mortality (60-fold increase at <130 mmol/L). 1, 2
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms. 1
• Never fail to monitor frequently during active correction - inadequate monitoring leads to overcorrection. 1

Monitoring Strategy

• Severe symptoms: Check sodium every 2 hours initially. 1
• Mild symptoms: Check sodium every 4 hours after symptom resolution. 1
• Asymptomatic: Check sodium daily during initial correction phase. 1