What is the initial approach to treating hyponatremia?

Initial Approach to Treating Hyponatremia

The initial approach to treating hyponatremia must be determined by three critical factors: symptom severity, volume status (hypovolemic, euvolemic, or hypervolemic), and the rapidity of onset (acute <48 hours versus chronic >48 hours). 1

Immediate Assessment

Before initiating treatment, rapidly assess the following:

• Symptom severity – Determine if the patient has severe symptoms (seizures, coma, altered consciousness, respiratory distress) versus mild symptoms (nausea, headache, weakness) versus asymptomatic presentation 1, 2
• Volume status – Examine for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemic); peripheral edema, ascites, jugular venous distention (hypervolemic); or absence of these findings (euvolemic) 1
• Serum and urine osmolality – Obtain serum osmolality to exclude pseudohyponatremia and urine osmolality to assess water excretion capacity 1
• Urine sodium concentration – A urine sodium <30 mmol/L suggests hypovolemic hyponatremia responsive to saline (71-100% positive predictive value), while >20-40 mmol/L with high urine osmolality suggests SIADH 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

For patients with seizures, coma, altered mental status, or respiratory distress, immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve. 1

• Administer 3% hypertonic saline as 100 mL boluses over 10 minutes, which can be repeated up to three times at 10-minute intervals until symptoms improve 1
• Critical safety limit: Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 3
• Monitor serum sodium every 2 hours during initial correction 1
• Consider ICU admission for close monitoring 1

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends on volume status:

Hypovolemic Hyponatremia:

• Discontinue diuretics immediately if sodium <125 mmol/L 1
• Administer isotonic saline (0.9% NaCl) for volume repletion at 15-20 mL/kg/h initially, then 4-14 mL/kg/h based on response 1
• Urine sodium <30 mmol/L predicts good response to saline (71-100% positive predictive value) 1

Euvolemic Hyponatremia (SIADH):

• Fluid restriction to 1 L/day is the cornerstone of treatment 1, 3
• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
• For resistant cases, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily) or urea 1, 4

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis):

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

Critical Correction Rate Guidelines

The single most important safety principle: Never exceed 8 mmol/L correction in 24 hours for chronic hyponatremia. 1, 3

• Standard correction rate: 4-8 mmol/L per day, not exceeding 10-12 mmol/L in 24 hours 1
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy) require even more cautious correction at 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1
• Acute hyponatremia (<48 hours onset) can be corrected more rapidly without risk of osmotic demyelination 1

Special Considerations for Neurosurgical Patients

In neurosurgical patients, distinguish between SIADH and cerebral salt wasting (CSW), as treatment approaches are fundamentally opposite. 1, 5

• SIADH: Euvolemic with urine sodium >20-40 mmol/L and urine osmolality >300 mOsm/kg – treat with fluid restriction 1
• CSW: True hypovolemia with low central venous pressure (<6 cm H₂O), urine sodium >20 mmol/L despite volume depletion – treat with volume and sodium replacement, NOT fluid restriction 1
• For severe CSW symptoms, administer 3% hypertonic saline plus fludrocortisone in ICU 1
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1

Common Pitfalls to Avoid

• Overly rapid correction exceeding 8 mmol/L in 24 hours causes osmotic demyelination syndrome 1, 3
• Using fluid restriction in cerebral salt wasting worsens outcomes 1
• Inadequate monitoring during active correction 1
• Failing to recognize and treat the underlying cause 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant – it increases fall risk (21% vs 5%) and mortality (60-fold increase for sodium <130 mmol/L) 1, 2, 3