What is the approach to managing hyponatremia?

Approach to Hyponatremia

Initial Assessment and Classification

Begin by confirming true hypotonic hyponatremia: check serum osmolality (<275 mOsm/kg) and exclude pseudohyponatremia from hyperglycemia by correcting sodium (add 1.6 mEq/L for each 100 mg/dL glucose >100 mg/dL). 1, 2

Obtain the following initial workup 1:

• Serum and urine osmolality to confirm hypotonic hyponatremia 1
• Urine sodium concentration to differentiate causes (spot urine sodium <30 mmol/L suggests hypovolemia with 71-100% positive predictive value for saline responsiveness) 1
• Serum uric acid (<4 mg/dL has 73-100% positive predictive value for SIADH) 1
• Thyroid function (TSH) and cortisol to exclude endocrine causes 1, 2
• Serum creatinine to assess renal function 1

Assess extracellular fluid volume status through physical examination 1, 2:

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
• Euvolemic signs: no edema, normal blood pressure, moist mucous membranes 1
• Hypervolemic signs: peripheral edema, ascites, jugular venous distention 1, 2

Note that physical examination alone has poor accuracy (sensitivity 41.1%, specificity 80%) for volume assessment 1

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Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

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

Specific protocol 1, 2:

• Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1, 2
• Monitor serum sodium every 2 hours during initial correction 1, 2
• Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2, 3, 4
• Consider ICU admission for close monitoring 1

Mild to Moderate Symptomatic or Asymptomatic Hyponatremia

Treatment depends on volume status and underlying cause (see below) 1, 2

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Treatment Based on Volume Status

Hypovolemic Hyponatremia

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

• Urine sodium <30 mmol/L predicts good response to saline (71-100% positive predictive value) 1
• Once euvolemic, reassess and treat underlying cause 1
• Maximum correction: 8 mmol/L in 24 hours 1, 2

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1, 2, 3

If no response to fluid restriction 1, 2:

• Add oral sodium chloride 100 mEq three times daily 1
• Consider urea (effective but poor palatability) 3
• Consider vasopressin receptor antagonists (vaptans) such as tolvaptan 15 mg once daily, titrating to 30-60 mg as needed 1, 5, 3

Common pitfall: Using fluid restriction in cerebral salt wasting (CSW) worsens outcomes—CSW requires volume and sodium replacement, not restriction 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L and treat the underlying condition. 1, 2, 4

Additional measures 1, 2:

• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• Consider albumin infusion in cirrhotic patients 1, 2
• Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens edema and ascites 1
• For persistent severe hyponatremia despite fluid restriction, consider tolvaptan with caution (higher risk of GI bleeding in cirrhosis: 10% vs 2% placebo) 1, 5

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Correction Rate Guidelines by Severity

The single most important principle: never exceed 8 mmol/L correction in 24 hours. 1, 2, 3, 4

Standard Correction Rates 1, 2:

• Serum sodium 126-135 mmol/L: Continue current therapy with close electrolyte monitoring 1
• Serum sodium 121-125 mmol/L: More cautious approach; consider stopping diuretics 1
• Serum sodium <120 mmol/L: Stop diuretics immediately; implement severe fluid restriction or volume expansion as appropriate 1, 2

High-Risk Patients Requiring Slower Correction (4-6 mmol/L per day, maximum 8 mmol/L in 24 hours) 1, 2:

• Advanced liver disease 1, 2
• Alcoholism 1, 2
• Malnutrition 1, 2
• Prior encephalopathy 1
• Severe hyponatremia (<120 mmol/L) 1

Rationale: These patients have higher risk of osmotic demyelination syndrome, which can cause dysarthria, dysphagia, oculomotor dysfunction, quadriparesis, or death, typically occurring 2-7 days after rapid correction 1

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Special Considerations for Neurosurgical Patients

In neurosurgical patients, distinguish between SIADH and cerebral salt wasting (CSW), as treatment approaches are opposite. 1

SIADH characteristics 1:

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

Cerebral Salt Wasting characteristics 1:

• True hypovolemia (CVP <6 cm H₂O)
• Urine sodium >20 mmol/L despite volume depletion
• Evidence of extracellular volume depletion
• Treatment: Volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1
• For severe symptoms: 3% hypertonic saline plus fludrocortisone in ICU 1

Critical pitfall: Fluid restriction in CSW worsens outcomes 1

In subarachnoid hemorrhage patients at risk of vasospasm: Do not use fluid restriction; consider fludrocortisone or hydrocortisone to prevent natriuresis 1

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Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, immediately intervene to prevent osmotic demyelination syndrome. 1, 2

Steps 1, 2:

1. Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1, 2
2. Consider administering desmopressin to slow or reverse the rapid rise 1, 2
3. Target: bring total 24-hour correction to no more than 8 mmol/L from starting point 1

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Monitoring During Treatment

Severe symptoms 1, 2:

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

Mild symptoms or asymptomatic 1, 2:

• Check every 4-6 hours initially 1
• Once stable, check daily until target sodium achieved 2

Watch for signs of osmotic demyelination syndrome 1:

• Dysarthria, dysphagia, oculomotor dysfunction, quadriparesis
• Typically occurs 2-7 days after rapid correction 1

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Common Pitfalls to Avoid

• Overly rapid correction (>8 mmol/L in 24 hours) leading to osmotic demyelination syndrome 1, 2, 3
• Inadequate monitoring during active correction 1
• Using fluid restriction in CSW (worsens outcomes) 1
• Failing to recognize and treat the underlying cause 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Ignoring mild hyponatremia (130-135 mmol/L)—even mild hyponatremia increases fall risk (21% vs 5%) and mortality (60-fold increase with sodium <130 mmol/L) 1, 3