How to manage a patient with hyponatremia?

Management of Hyponatremia

Initial Assessment and Classification

Hyponatremia (serum sodium <135 mmol/L) requires immediate evaluation based on symptom severity, volume status, and serum osmolality to guide treatment and prevent complications. 1

• Obtain serum and urine osmolality, urine sodium, urine electrolytes, serum uric acid, and assess extracellular fluid volume status through physical examination 1
• Check serum creatinine, thyroid-stimulating hormone (TSH), and cortisol to exclude secondary causes 1
• Classify severity: mild (130-135 mmol/L), moderate (120-129 mmol/L), severe (<120 mmol/L) 1, 2
• Determine acuity: acute (<48 hours) versus chronic (>48 hours), as this fundamentally changes correction rates 1, 3
• Assess volume status: hypovolemic (orthostatic hypotension, dry mucous membranes, decreased skin turgor), euvolemic (normal volume status), or hypervolemic (peripheral edema, ascites, jugular venous distention) 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

For patients with severe symptoms (seizures, coma, altered mental status, respiratory distress), immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until symptoms resolve. 1, 4, 2

• Give 100 mL boluses of 3% hypertonic saline over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1
• Never exceed total correction of 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 5, 4
• Monitor serum sodium every 2 hours during initial correction phase 1
• Admit to ICU for close monitoring during active correction 1

Moderate Symptomatic Hyponatremia

• For patients with nausea, vomiting, confusion, headache, or gait instability, hospital admission is required for monitored correction 1, 6
• Correction rate should be 4-6 mmol/L per day, not exceeding 8 mmol/L in 24 hours 1
• Monitor serum sodium every 4-6 hours initially 1

Asymptomatic or Mildly Symptomatic Hyponatremia

• Treatment focuses on addressing the underlying cause and volume status 1
• Correction rate should be slower: 4-6 mmol/L per day maximum 1
• Monitor serum sodium every 24-48 hours initially 1

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion. 1, 2

• Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on clinical response 1
• Urine sodium <30 mmol/L predicts good response to saline infusion (positive predictive value 71-100%) 1
• Continue isotonic saline until euvolemia is achieved 1
• Maximum correction: 8 mmol/L in 24 hours 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1, 4, 2

• If no response to fluid restriction after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1, 7
• For persistent hyponatremia despite fluid restriction, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1, 5
• Tolvaptan must be initiated in hospital with close sodium monitoring due to risk of overly rapid correction 5
• For severe symptomatic SIADH, use 3% hypertonic saline as described above 1

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 ascites and edema 1
• Sodium restriction (2-2.5 g/day) is more effective than fluid restriction for weight loss in cirrhosis, as fluid follows sodium 1
• For heart failure patients with persistent severe hyponatremia despite fluid restriction and guideline-directed medical therapy, consider short-term vasopressin antagonists 1

Special Populations and High-Risk Considerations

Patients with Advanced Liver Disease, Alcoholism, or Malnutrition

These patients require even more cautious correction at 4-6 mmol/L per day (maximum 8 mmol/L in 24 hours) due to significantly higher risk of osmotic demyelination syndrome. 1, 5, 4

• Cirrhotic patients with hyponatremia have increased 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

Neurosurgical Patients

Distinguish between SIADH and cerebral salt wasting (CSW), as they require opposite treatments. 1

• SIADH: Euvolemic state, urine sodium >20-40 mmol/L, urine osmolality >300 mOsm/kg; treat with fluid restriction 1
• CSW: True hypovolemia (CVP <6 cm H₂O), urine sodium >20 mmol/L despite volume depletion; treat with volume and sodium replacement, NOT fluid restriction 1
• For CSW with severe symptoms, use 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily 1
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1
• Consider fludrocortisone or hydrocortisone to prevent natriuresis in subarachnoid hemorrhage patients 1

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, immediately discontinue current fluids and switch to D5W (5% dextrose in water). 1

• Consider administering desmopressin to slow or reverse the rapid rise in serum sodium 1
• Target reduction to bring total 24-hour correction to no more than 8 mmol/L from starting point 1
• Monitor for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1, 5

Critical Pitfalls to Avoid

• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—this causes osmotic demyelination syndrome 1, 5, 4
• Never use fluid restriction in cerebral salt wasting—this worsens outcomes 1
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Never ignore mild hyponatremia (130-135 mmol/L) as clinically insignificant—it increases fall risk (21% vs 5%), mortality (60-fold increase with sodium <130 mmol/L), and cognitive impairment 1, 6, 4
• Never use hypotonic fluids (lactated Ringer's, 0.45% saline) in patients with hyponatremia—they worsen the condition 1
• Inadequate monitoring during active correction can lead to osmotic demyelination syndrome 1
• Failing to recognize and treat the underlying cause leads to poor outcomes 1

Monitoring Requirements

• Severe symptoms: Check serum sodium every 2 hours during initial correction 1
• Moderate symptoms: Check serum sodium every 4-6 hours initially 1
• Mild symptoms or asymptomatic: Check serum sodium every 24-48 hours initially 1
• Monitor for neurological changes, volume status, and urine output throughout treatment 1
• After discontinuation of treatment, resume fluid restriction and monitor for changes in sodium and volume status 5