How do you manage a patient with hyponatremia?

Management of Hyponatremia

Hyponatremia (serum sodium <135 mmol/L) requires a systematic approach based on symptom severity, volume status, and chronicity, with the primary goal of preventing both neurologic complications from hyponatremia itself and osmotic demyelination syndrome from overly rapid correction. 1

Initial Assessment and Classification

Determine symptom severity first, as this dictates urgency of treatment 1:

• Severe symptoms (seizures, coma, altered mental status, cardiorespiratory distress) require immediate hypertonic saline 1, 2
• Moderate symptoms (nausea, vomiting, confusion, headache) warrant hospital admission with monitored correction 1
• Mild/asymptomatic cases allow for outpatient management in most instances 1

Assess volume status through physical examination 1:

• 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

Obtain essential laboratory studies 1:

• Serum osmolality, urine osmolality, and urine sodium concentration 1
• Serum creatinine, glucose, thyroid function, and cortisol if indicated 1
• Urine sodium <30 mmol/L predicts saline responsiveness with 71-100% positive predictive value 1
• Serum uric acid <4 mg/dL suggests SIADH with 73-100% positive predictive value 1

Critical Correction Rate Guidelines

The single most important safety principle: never exceed 8 mmol/L correction in 24 hours 1, 3, 2:

• Standard patients: 4-8 mmol/L per day, maximum 10-12 mmol/L in 24 hours 1
• High-risk patients (advanced liver disease, alcoholism, malnutrition, severe hyponatremia <120 mmol/L): 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 3
• Tolvaptan carries FDA black box warning: initiate only in hospital with close sodium monitoring due to risk of overly rapid correction (>12 mEq/L/24 hours can cause osmotic demyelination) 3

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

Administer 3% hypertonic saline immediately 1, 2, 4:

• Give 100-150 mL bolus over 10 minutes, can repeat up to 3 times at 10-minute intervals 1, 4
• Target: increase sodium by 4-6 mmol/L over first 1-2 hours or until severe symptoms resolve 1, 2, 4
• Monitor serum sodium every 2 hours during initial correction 1
• Stop hypertonic saline once symptoms resolve or 6 mmol/L increase achieved 1
• Total correction must not exceed 8 mmol/L in 24 hours 1, 3

Mild to Moderate Symptomatic or Asymptomatic Hyponatremia

Treatment depends on volume status and underlying cause 1:

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Administer isotonic saline (0.9% NaCl) for volume repletion 1, 5:

• Initial rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
• Discontinue diuretics immediately if sodium <125 mmol/L 1
• Monitor for euvolemia: resolution of orthostatic hypotension, normal skin turgor, stable vital signs 1
• Once euvolemic, switch to maintenance isotonic fluids at 30 mL/kg/day 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment 1, 2, 6:

• First-line: Restrict fluids to 500-1000 mL/day 1, 4
• If no response after 24-48 hours: Add oral sodium chloride 100 mEq (2.3 g) three times daily 1
• Second-line pharmacologic options 1, 4:
  • Urea 15-30 g/day in divided doses (very effective and safe per recent evidence) 4, 6
  • Tolvaptan 15 mg once daily, titrate to 30-60 mg (use with extreme caution, only in hospital setting) 3, 6
  • Demeclocycline or lithium (less commonly used due to side effects) 1

Important: Nearly half of SIADH patients do not respond to fluid restriction alone 4

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Fluid restriction is primary treatment 1, 2, 5:

• Restrict fluids to 1-1.5 L/day for sodium <125 mmol/L 1, 5
• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• For cirrhosis: Consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens edema and ascites 1
• Sodium restriction (not fluid restriction) results in weight loss as fluid follows sodium 1
• Tolvaptan may be considered for persistent severe hyponatremia despite fluid restriction, but carries higher risk of GI bleeding in cirrhosis (10% vs 2% placebo) 1, 3

Special Populations and Critical Distinctions

Neurosurgical Patients: SIADH vs Cerebral Salt Wasting (CSW)

Distinguishing these conditions is critical as treatments are opposite 1:

SIADH characteristics 1:

• Euvolemic state (normal CVP 8-12 cm H₂O)
• Urine sodium >20-40 mmol/L
• Urine osmolality >300 mOsm/kg
• Treatment: Fluid restriction to 1 L/day

Cerebral Salt Wasting characteristics 1:

• True hypovolemia (CVP <6 cm H₂O)
• Urine sodium >20 mmol/L despite volume depletion
• Clinical signs: hypotension, tachycardia, dry mucous membranes
• Treatment: Volume and sodium replacement with isotonic or hypertonic saline, fludrocortisone 0.1-0.2 mg daily for severe cases

Never use fluid restriction in CSW or subarachnoid hemorrhage patients at risk of vasospasm—this worsens outcomes 1

Cirrhotic Patients

Require more cautious correction (4-6 mmol/L per day maximum) 1:

• Hyponatremia increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• Sodium ≤130 mmol/L associated with 60-fold increase in mortality (11.2% vs 0.19%) 1, 2
• Only 1.2% of cirrhotic patients with ascites have sodium ≤120 mmol/L 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) 1
• Consider administering desmopressin to slow or reverse rapid rise 1
• Target: Bring total 24-hour correction to no more than 8 mmol/L from starting point 1
• Watch for osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1, 3

Monitoring Protocols

Frequency of sodium monitoring 1:

• Severe symptoms: Every 2 hours during initial correction 1
• Moderate symptoms: Every 4 hours after symptom resolution 1
• Mild/asymptomatic: Every 24-48 hours initially 1

Common Pitfalls to Avoid

Critical errors that worsen outcomes 1:

• Using fluid restriction in CSW or subarachnoid hemorrhage patients—this is contraindicated 1
• Correcting chronic hyponatremia faster than 8 mmol/L in 24 hours—causes osmotic demyelination syndrome 1, 3
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—worsens fluid overload 1
• Ignoring mild hyponatremia (130-135 mmol/L)—associated with increased falls (21% vs 5%) and mortality 1, 2
• Inadequate monitoring during active correction—risks overcorrection 1
• Using lactated Ringer's solution for hyponatremia—it is hypotonic (130 mEq/L sodium) and can worsen hyponatremia 1

Medication Considerations

Tolvaptan (Vaptan) use requires extreme caution 3:

• FDA-approved only for euvolemic or hypervolemic hyponatremia with sodium <125 mEq/L or symptomatic hyponatremia resistant to fluid restriction 3
• Must initiate and re-initiate only in hospital with close sodium monitoring 3
• Starting dose: 15 mg once daily, titrate to 30-60 mg based on response 3
• Do not use for more than 30 days to minimize liver injury risk 3
• Contraindicated in: Hypovolemic hyponatremia, patients unable to sense thirst, anuria, concurrent strong CYP3A inhibitors 3
• Higher risk in cirrhosis: GI bleeding (10% vs 2%), avoid unless persistent severe hyponatremia despite other measures 1, 3