What is the management for a patient with severe hyponatremia (sodium level of 110 mmol/L)?

Management of Severe Hyponatremia (Sodium 110 mmol/L)

Immediate Assessment and Classification

A sodium level of 110 mmol/L represents severe, life-threatening hyponatremia requiring urgent intervention based on symptom severity, not the number alone. 1

Determine Symptom Severity (Dictates Treatment Urgency)

• Severe symptoms (seizures, coma, altered mental status, cardiorespiratory distress): This is a medical emergency requiring immediate hypertonic saline 1, 2
• Moderate symptoms (nausea, vomiting, confusion, headache, gait instability): Requires hospital admission with monitored correction 1, 3
• Mild/asymptomatic: Slower correction is safer, but sodium this low still warrants aggressive workup 1, 4

Assess Volume Status (Dictates Underlying Cause and Treatment)

• 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, pulmonary congestion 1, 5

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Emergency Treatment for Severe Symptomatic Hyponatremia

If the patient has seizures, coma, or severe altered mental status, immediately administer 3% hypertonic saline as 100 mL IV bolus over 10 minutes. 1, 2

• Target correction: Increase sodium by 4-6 mmol/L over the first 1-6 hours or until severe symptoms resolve 1, 2
• Repeat boluses: Can give up to three 100 mL boluses at 10-minute intervals if symptoms persist 1
• Maximum correction limit: Never exceed 8 mmol/L increase in 24 hours (some guidelines allow 10 mmol/L, but 8 mmol/L is safer for chronic hyponatremia) 1, 2, 4
• Monitoring: Check serum sodium every 2 hours during initial correction phase 1

Critical Safety Point: Osmotic Demyelination Syndrome

• Overly rapid correction (>8 mmol/L in 24 hours) causes osmotic demyelination syndrome, presenting 2-7 days later with dysarthria, dysphagia, quadriparesis, or locked-in syndrome 1, 2
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy, severe hyponatremia <120 mmol/L) require even slower correction at 4-6 mmol/L per day 1, 4

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Treatment Based on Volume Status

Hypovolemic Hyponatremia (True Volume Depletion)

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, 3

• Diagnostic clue: Urine sodium <30 mmol/L predicts saline responsiveness with 71-100% positive predictive value 1
• Causes: Gastrointestinal losses (vomiting, diarrhea), diuretic overuse, burns, third-spacing 1, 5
• Once euvolemic: Switch to maintenance isotonic fluids at 30 mL/kg/day 1
• Avoid: Hypotonic fluids (lactated Ringer's, 0.45% saline, D5W) which worsen hyponatremia 1, 6

Euvolemic Hyponatremia (SIADH Most Common)

Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1, 3

• If no response to fluid restriction: Add oral sodium chloride 100 mEq (approximately 6 grams) three times daily 1
• For severe symptoms: Use 3% hypertonic saline as described above, then transition to fluid restriction once symptoms resolve 1, 2
• Second-line pharmacological options:
  • Urea 15-30 grams twice daily (very effective, poor palatability) 1, 4
  • Tolvaptan 15 mg once daily, titrate to 30-60 mg (risk of overly rapid correction, increased thirst) 1, 7, 2
• Diagnostic criteria for SIADH: Euvolemia, urine osmolality >100 mOsm/kg (typically >300), urine sodium >20-40 mmol/L, normal thyroid/adrenal function 1, 5

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day and discontinue diuretics temporarily if sodium <125 mmol/L. 1, 3

• For cirrhotic patients: Consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens fluid overload 1, 6
• Sodium restriction (not fluid restriction) results in weight loss, as fluid follows sodium 1
• Vaptans (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, 7

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Calculating Sodium Deficit and Correction Rate

Sodium deficit = Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1

• Example: For a 70 kg patient with Na 110, to increase by 6 mEq/L: 6 × (0.5 × 70) = 210 mEq sodium needed
• 3% hypertonic saline contains 513 mEq/L sodium: 210 mEq ÷ 513 = approximately 410 mL over 6 hours
• After initial 6 mmol/L correction: Only 2 mmol/L additional correction allowed in next 18 hours to stay within 8 mmol/L/24-hour limit 1

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Essential Diagnostic Workup (Do Not Delay Treatment)

• Serum osmolality: Exclude pseudohyponatremia (normal 275-290 mOsm/kg) 1, 5
• Urine osmolality and urine sodium: Differentiate causes 1, 3
• Serum glucose: Hyperglycemia causes pseudohyponatremia (add 1.6 mEq/L to sodium for each 100 mg/dL glucose >100) 1
• TSH and cortisol: Rule out hypothyroidism and adrenal insufficiency 1
• Serum uric acid: <4 mg/dL suggests SIADH with 73-100% positive predictive value 1

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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, 4

• Consider desmopressin (2-4 mcg IV/SC) to slow or reverse rapid rise 1
• Goal: Bring total 24-hour correction back to ≤8 mmol/L from starting point 1
• Monitor closely: Osmotic demyelination typically occurs 2-7 days after overcorrection 1, 2

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Special Populations and Pitfalls

Neurosurgical Patients: Distinguish SIADH from Cerebral Salt Wasting (CSW)

• CSW requires volume and sodium replacement (isotonic or hypertonic saline), NOT fluid restriction 1
• CSW characteristics: True hypovolemia (CVP <6 cm H₂O), urine sodium >20 mmol/L despite volume depletion, orthostatic hypotension 1
• Treatment for CSW: Normal saline 50-100 mL/kg/day, fludrocortisone 0.1-0.2 mg daily for severe symptoms 1
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1

Cirrhotic Patients

• Require more cautious correction (4-6 mmol/L per day, maximum 8 mmol/L in 24 hours) due to higher risk of osmotic demyelination 1, 4
• Hyponatremia in cirrhosis increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1

Alcoholic Patients

• Extremely high risk for osmotic demyelination: Limit correction to 4-6 mmol/L per day 1, 4
• Beer potomania: Discontinuing alcohol and providing adequate dietary sodium can dramatically improve hyponatremia 1

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Common Pitfalls to Avoid

• Never use fluid restriction as initial treatment for severe symptomatic hyponatremia—this is a medical emergency requiring hypertonic saline 1, 2
• Never exceed 8 mmol/L correction in 24 hours in chronic or unknown-duration hyponatremia 1, 4
• 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 Na <130) 1, 2
• Never use lactated Ringer's for hyponatremia treatment—it is hypotonic (130 mEq/L sodium) and worsens hyponatremia 1