How to manage a patient with severe hyponatremia (low serum sodium level), particularly those who are symptomatic?

Management of Severe Hyponatremia

For severe symptomatic hyponatremia (seizures, altered mental status, coma), immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until symptoms resolve, but never exceed 8 mmol/L total correction in 24 hours to prevent osmotic demyelination syndrome. 1

Immediate Assessment and Classification

Determine symptom severity first—this dictates urgency:

• Severe symptoms (seizures, coma, respiratory arrest, altered mental status) require immediate hypertonic saline 1, 2
• Moderate symptoms (nausea, vomiting, confusion, headache) warrant hospital admission with monitored correction 1, 3
• Mild/asymptomatic cases allow for more conservative management 1

Assess volume status through physical examination:

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
• Euvolemic: no edema, normal blood pressure, normal skin turgor 1
• Hypervolemic signs: peripheral edema, ascites, jugular venous distention 1

Obtain essential labs immediately:

• Serum osmolality, urine osmolality, urine sodium, serum uric acid 1
• Urine sodium <30 mmol/L predicts saline responsiveness (71-100% positive predictive value) 1
• Serum uric acid <4 mg/dL suggests SIADH (73-100% positive predictive value) 1

Treatment Algorithm Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

Administer 3% hypertonic saline immediately:

• Give 100 mL bolus over 10 minutes, can repeat up to 3 times at 10-minute intervals 1
• Target: increase sodium by 6 mmol/L over first 6 hours or until symptoms resolve 1, 4
• Critical safety limit: never exceed 8 mmol/L correction in 24 hours 1, 5
• After initial 6 mmol/L correction, limit to only 2 mmol/L additional in next 18 hours 4

Monitor serum sodium every 2 hours during active correction 1

Discontinue 3% saline when:

• Severe symptoms resolve 4
• 6 mmol/L correction achieved 4
• Switch to maintenance protocol and check sodium every 4 hours 4

Moderate Symptomatic or Asymptomatic Hyponatremia

Treatment depends on volume status:

For hypovolemic hyponatremia:

• Discontinue diuretics immediately 1
• Administer isotonic saline (0.9% NaCl) at 15-20 mL/kg/h initially, then 4-14 mL/kg/h based on response 1
• Urine sodium <30 mmol/L confirms appropriate indication for saline 1

For euvolemic hyponatremia (SIADH):

• Fluid restriction to 1 L/day is first-line treatment 1
• If no response, add oral sodium chloride 100 mEq three times daily 1, 6
• Consider vaptans (tolvaptan 15 mg daily, titrate to 30-60 mg) for resistant cases 1, 7

For hypervolemic hyponatremia (heart failure, cirrhosis):

• Fluid restriction to 1-1.5 L/day for 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 present—it worsens fluid overload 1

Critical Correction Rate Guidelines

Standard correction limits (prevent osmotic demyelination):

• Maximum 8 mmol/L in 24 hours for most patients 1, 2, 5
• Maximum 10-12 mmol/L in 48 hours 5
• Average rate should not exceed 0.55 mmol/L per hour to reach sodium of 120 mmol/L 5

High-risk patients require slower correction (4-6 mmol/L per day, max 8 mmol/L in 24 hours):

• Advanced liver disease 1
• Alcoholism 1
• Malnutrition 1
• Severe hyponatremia (<120 mmol/L) 1
• Prior encephalopathy 1

Special Populations and Pitfalls

Neurosurgical patients—distinguish SIADH from cerebral salt wasting (CSW):

• SIADH: euvolemic, treat with fluid restriction 1
• CSW: hypovolemic (CVP <6 cm H₂O), treat with volume and sodium replacement, never fluid restriction 1
• In subarachnoid hemorrhage at risk for vasospasm, avoid fluid restriction entirely 1
• Consider fludrocortisone 0.1-0.2 mg daily for CSW 1

Cirrhotic patients:

• Hyponatremia increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), hepatic encephalopathy (OR 2.36) 1
• Require cautious correction: 4-6 mmol/L per day maximum 1
• Tolvaptan carries higher gastrointestinal bleeding risk (10% vs 2% placebo) 1

Common pitfalls to avoid:

• Overly rapid correction >8 mmol/L in 24 hours causes osmotic demyelination syndrome 1, 8, 2
• Using fluid restriction in CSW worsens outcomes 1
• Inadequate monitoring during active correction 1
• Ignoring mild hyponatremia (130-135 mmol/L)—associated with increased falls (21% vs 5%) and 60-fold mortality increase when <130 mmol/L 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 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 desmopressin to slow or reverse rapid rise 1, 8
• Target: relower sodium to bring total 24-hour correction to ≤8 mmol/L from baseline 1

Watch for osmotic demyelination syndrome (typically 2-7 days post-correction):

• Dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 1
• Risk highest in patients with liver disease, alcoholism, malnutrition 1, 8

Calculating Sodium Deficit

Use formula: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1, 6

This helps determine appropriate sodium supplementation needed while respecting correction limits.