What is the appropriate management approach for a patient presenting with hyponatremia?

Management of Hyponatremia

Hyponatremia (serum sodium <135 mmol/L) requires immediate assessment of volume status and symptom severity to guide treatment, with the critical principle being to never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome. 1

Initial Assessment and Classification

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

• Severe symptoms (seizures, coma, altered consciousness, respiratory distress) constitute a medical emergency requiring immediate hypertonic saline 1, 2
• Moderate symptoms (confusion, nausea, vomiting, headache, gait instability) warrant hospital admission with monitored correction 1, 2
• Mild/asymptomatic cases allow for more conservative outpatient management 1, 3

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 tests 1:

• Serum and urine osmolality 1
• Urine sodium concentration 1
• Serum uric acid (if <4 mg/dL, suggests SIADH with 73-100% positive predictive value) 1
• Thyroid function and cortisol to exclude endocrine causes 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

Administer 3% hypertonic saline immediately with the following protocol 1, 3:

• Initial goal: Correct by 6 mmol/L over 6 hours OR until severe symptoms resolve 1
• Administration: 100 mL boluses over 10 minutes, can repeat up to 3 times at 10-minute intervals 1
• Maximum correction: Never exceed 8 mmol/L in 24 hours 1, 3
• Monitoring: Check serum sodium every 2 hours during initial correction 1

Critical safety consideration: If you correct 6 mmol/L in the first 6 hours, only 2 mmol/L additional correction is allowed in the next 18 hours 1

Mild to Moderate Symptomatic or Asymptomatic Hyponatremia

Treatment depends entirely on volume status 1, 3:

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 1, 4:

• Initial rate: 15-20 mL/kg/h 1
• Subsequent rate: 4-14 mL/kg/h based on response 1
• Predictive indicator: Urine sodium <30 mmol/L has 71-100% positive predictive value for saline responsiveness 1

Continue until euvolemia is achieved, then reassess 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment 1, 3, 4:

• First-line: Restrict fluids to <1000 mL/day 1
• If no response: Add oral sodium chloride 100 mEq (2.3 grams) three times daily 1
• Pharmacological options for resistant cases 1, 3:
  • Tolvaptan 15 mg once daily, titrate to 30-60 mg 1
  • Urea 15-30 grams daily (divided doses) 1
  • Demeclocycline or lithium (less commonly used due to side effects) 1

Monitor serum sodium every 24 hours initially 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 3, 4

Temporarily discontinue diuretics if sodium <125 mmol/L 1

For cirrhotic patients specifically 1:

• Consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens ascites and edema 1
• Sodium restriction (not fluid restriction) results in weight loss as fluid follows sodium 1

Vasopressin 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

Critical Correction Rate Guidelines

Standard correction rates 1, 3, 5:

• Maximum for all patients: 8 mmol/L per 24 hours 1, 3
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 5

Acute hyponatremia (<48 hours) can be corrected more rapidly without risk of osmotic demyelination 1

Chronic hyponatremia (>48 hours) requires slower correction to prevent osmotic demyelination syndrome 1, 5

Special Populations and Considerations

Neurosurgical Patients

Distinguish between SIADH and Cerebral Salt Wasting (CSW) as they require opposite treatments 1:

SIADH characteristics 1:

• Euvolemic state 1
• Urine sodium >20-40 mmol/L 1
• Urine osmolality >300 mOsm/kg 1
• Treatment: Fluid restriction 1

CSW characteristics 1:

• True hypovolemia with low CVP (<6 cm H₂O) 1
• Urine sodium >20 mmol/L despite volume depletion 1
• Clinical signs of volume depletion 1
• Treatment: Volume and sodium replacement with isotonic or hypertonic saline 1
• For severe symptoms: Add fludrocortisone 0.1-0.2 mg daily 1

Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1

Cirrhotic Patients

Even mild hyponatremia (sodium <130 mmol/L) significantly increases risk 1:

• Spontaneous bacterial peritonitis (OR 3.40) 1
• Hepatorenal syndrome (OR 3.45) 1
• Hepatic encephalopathy (OR 2.36) 1
• 60-fold increase in hospital mortality (11.2% vs 0.19%) 1

Require more cautious correction (4-6 mmol/L per day) due to higher risk of osmotic demyelination 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 the rapid rise 1
• Goal: Bring total 24-hour correction to no more than 8 mmol/L from starting point 1

Common Pitfalls to Avoid

Never ignore mild hyponatremia (130-135 mmol/L) as it increases fall risk (21% vs 5%), mortality, and cognitive impairment 1, 2, 3

Never use fluid restriction in cerebral salt wasting as this worsens outcomes 1

Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 3, 5

Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms, as it worsens fluid overload 1

Never rely on physical examination alone for volume assessment (sensitivity 41.1%, specificity 80%) - use urine studies to confirm 1

Inadequate monitoring during active correction leads to overcorrection and osmotic demyelination 1

Failing to identify and treat the underlying cause results in recurrent hyponatremia 1

Monitoring Protocol

For severe symptoms 1:

• Check serum sodium every 2 hours during initial correction 1
• After symptom resolution, check every 4 hours 1

For mild symptoms or asymptomatic 1:

• Check serum sodium every 24 hours initially 1
• Adjust frequency based on response 1

Watch for signs of osmotic demyelination syndrome (typically occurring 2-7 days after rapid correction): dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 1