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

Initial Approach to Treating Hyponatremia

The initial approach to treating hyponatremia depends on symptom severity and volume status: severely symptomatic patients require immediate 3% hypertonic saline to correct sodium by 6 mmol/L over 6 hours, while asymptomatic patients need volume status assessment (hypovolemic, euvolemic, or hypervolemic) to guide specific therapy, with the critical safety principle being never to exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome. 1

Immediate Assessment: Symptom Severity First

Determine if the patient has severe symptoms (seizures, coma, altered mental status, cardiorespiratory distress) versus mild symptoms (nausea, headache, confusion) versus asymptomatic presentation. 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: 6 mmol/L over the first 6 hours or until severe symptoms resolve. 1
• Monitor serum sodium every 2 hours during initial correction phase. 1
• Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1, 2

For Asymptomatic or Mildly Symptomatic Hyponatremia

Assess volume status through physical examination to categorize as hypovolemic, euvolemic, or hypervolemic—this determines the treatment pathway. 1, 2

Volume Status Assessment and Initial Workup

Obtain the following tests immediately: 1

• Serum osmolality (to exclude pseudohyponatremia)
• Urine osmolality and urine sodium concentration
• Serum and urine electrolytes
• Serum uric acid (levels <4 mg/dL suggest SIADH with 73-100% positive predictive value)
• Assessment of extracellular fluid volume status

Physical examination findings to determine volume status: 1

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins
• Euvolemic signs: normal blood pressure, no edema, moist mucous membranes
• Hypervolemic signs: peripheral edema, ascites, jugular venous distention, pulmonary congestion

Treatment Based 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 infusion (71-100% positive predictive value). 1

Euvolemic Hyponatremia (SIADH)

• Fluid restriction to 1 L/day is the cornerstone of treatment. 1, 2
• Add oral sodium chloride 100 mEq three times daily if no response to fluid restriction. 1
• For severe symptoms: use 3% hypertonic saline as described above. 1
• Second-line options for resistant cases: urea, vasopressin receptor antagonists (tolvaptan 15 mg once daily), demeclocycline, or lithium. 1, 3

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

• Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L. 1, 2
• 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
• Vasopressin receptor antagonists (tolvaptan) may be considered for persistent severe hyponatremia despite fluid restriction, but use with extreme caution in cirrhosis due to higher risk of gastrointestinal bleeding (10% vs 2% placebo). 1, 4

Critical Correction Rate Guidelines

Standard correction rates to prevent osmotic demyelination syndrome: 1, 2

• Maximum correction: 8 mmol/L in 24 hours for most patients
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): limit to 4-6 mmol/L per day
• Never exceed 1 mmol/L/hour for chronic hyponatremia

Special Considerations for Neurosurgical Patients

Distinguish between SIADH and cerebral salt wasting (CSW) as treatments are opposite: 1, 5

• SIADH: euvolemic, treat with fluid restriction
• CSW: hypovolemic with urine sodium >20 mmol/L despite volume depletion, treat with volume and sodium replacement (NOT fluid restriction)
• For CSW with severe symptoms: use 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily in ICU. 1
• In subarachnoid hemorrhage patients at risk of vasospasm: avoid fluid restriction, consider fludrocortisone or hydrocortisone. 1

Common Pitfalls to Avoid

• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—this causes osmotic demyelination syndrome (dysarthria, dysphagia, quadriparesis, oculomotor dysfunction typically 2-7 days after rapid correction). 1, 2
• 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 with sodium <130 mmol/L). 1, 2
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—it worsens fluid overload. 1
• Never fail to monitor adequately during active correction—check sodium every 2 hours for severe symptoms, every 4 hours after symptom resolution. 1

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours: 1

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water)
• Consider administering desmopressin to slow or reverse the rapid rise in serum sodium
• Goal: relower sodium to bring total 24-hour correction to no more than 8 mmol/L from starting point