How should hyponatremia be evaluated and managed in an older adult, considering symptom severity, acute (<48 h) versus chronic (≥48 h) duration, volume status (hypovolemic, euvolemic, hypervolemic), and underlying causes?

Hyponatremia Evaluation and Management in Older Adults

Initial Diagnostic Workup

Hyponatremia (serum sodium <135 mmol/L) requires immediate assessment of symptom severity, duration, volume status, and serum osmolality to guide treatment and prevent life-threatening complications. 1

Essential Laboratory Tests

• Serum osmolality to exclude pseudohyponatremia (from hyperglycemia or hyperlipidemia) 1, 2
• Urine osmolality and urine sodium concentration to differentiate causes 1, 2
• Serum and urine electrolytes, uric acid (serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH) 1
• Thyroid-stimulating hormone (TSH) to exclude hypothyroidism 1
• Serum creatinine and blood urea nitrogen to assess renal function 1

Volume Status Assessment

Physical examination alone has poor accuracy (sensitivity 41%, specificity 80%), so integrate multiple clinical findings: 1

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

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Management Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

For patients with seizures, coma, altered consciousness, or respiratory distress, immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve. 1, 3

• Dosing: 100 mL boluses of 3% NaCl IV over 10 minutes, repeat up to 3 times at 10-minute intervals 1
• Maximum correction: Never exceed 8 mmol/L in any 24-hour period to prevent osmotic demyelination syndrome 1, 3
• Monitoring: Check serum sodium every 2 hours during initial correction 1
• ICU admission for close monitoring during treatment 1

Mild to Moderate Symptomatic Hyponatremia

Symptoms include nausea, vomiting, headache, confusion, gait instability, and weakness. 4, 3

• Treatment depends on volume status (see below) 1
• Correction rate: 4-8 mmol/L per day, maximum 8 mmol/L in 24 hours 1
• Monitor sodium every 4-6 hours after symptom resolution 1

Asymptomatic Chronic Hyponatremia

Even mild chronic hyponatremia (130-135 mmol/L) is not benign and increases mortality 60-fold (11.2% vs 0.19%), fall risk (21% vs 5%), and causes cognitive impairment. 4, 3

• Requires treatment based on underlying cause and volume status 1, 4
• Slower correction: 4-6 mmol/L per day in high-risk patients 1

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Management Based on Volume Status

Hypovolemic Hyponatremia

Characterized by ECF volume depletion with urine sodium <30 mmol/L (extrarenal losses) or >20 mmol/L (renal losses). 1

Treatment:

• Discontinue diuretics immediately if sodium <125 mmol/L 1
• 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
• Urine sodium <30 mmol/L predicts 71-100% response to saline infusion 1
• Maximum correction: 8 mmol/L in 24 hours 1

Euvolemic Hyponatremia (SIADH)

Diagnosis requires: hypotonic hyponatremia, urine osmolality >100 mOsm/kg (typically >300), urine sodium >20-40 mmol/L, normal thyroid/adrenal function, and clinical euvolemia. 1, 2

Treatment:

• Fluid restriction to 1 L/day is first-line therapy 1, 3
• If no response: Add oral sodium chloride 100 mEq three times daily 1
• For resistant cases: Consider vasopressin receptor antagonists (tolvaptan 15 mg daily, titrate to 30-60 mg), urea, demeclocycline, or loop diuretics 1, 3
• For severe symptoms: 3% hypertonic saline with careful monitoring 1

Common causes: malignancy (especially small cell lung cancer), CNS disorders, pulmonary disease, medications (SSRIs, carbamazepine, cyclophosphamide, NSAIDs, opioids) 1

Hypervolemic Hyponatremia

Seen in heart failure, cirrhosis, nephrotic syndrome—characterized by total body sodium excess with even greater water excess. 1

Treatment:

• Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 3
• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• For cirrhosis: Consider albumin infusion (8 g per liter of ascites removed) alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens edema and ascites 1
• Treat underlying condition (optimize heart failure therapy, manage cirrhosis) 1, 5
• Vasopressin receptor antagonists may be considered for persistent severe hyponatremia despite fluid restriction 1, 3

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Special Considerations for Older Adults

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

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

These patients have 0.5-1.5% risk of osmotic demyelination syndrome even with careful correction. 1

Acute vs. Chronic Hyponatremia

Duration determines correction strategy:

• Acute (<48 hours): Can be corrected more rapidly without risk of osmotic demyelination; severe symptoms require immediate hypertonic saline 1, 4
• Chronic (≥48 hours or unknown): Brain has adapted by reducing intracellular osmoles; rapid correction causes osmotic demyelination syndrome 1, 2
• When duration unknown: Assume chronic and correct slowly 1

Neurosurgical Patients: SIADH vs. Cerebral Salt Wasting (CSW)

Critical distinction because treatments are opposite: 1

SIADH (euvolemic):

• Urine sodium >20-40 mmol/L, urine osmolality >300 mOsm/kg
• Normal to slightly elevated CVP
• Treatment: Fluid restriction 1

CSW (hypovolemic):

• Urine sodium >20 mmol/L despite volume depletion
• Low CVP (<6 cm H₂O), clinical hypovolemia
• Treatment: Volume and sodium replacement with isotonic or hypertonic saline, fludrocortisone 0.1-0.2 mg daily for severe cases 1
• Never use fluid restriction in CSW—it worsens outcomes 1

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Management of Overcorrection

If sodium rises >8 mmol/L in 24 hours: 1

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Consider desmopressin to slow or reverse rapid sodium rise 1
• Target: Bring total 24-hour correction back to ≤8 mmol/L from baseline 1
• Watch for osmotic demyelination syndrome 2-7 days after overcorrection: dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 1

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Common Pitfalls to Avoid

• Overly rapid correction exceeding 8 mmol/L in 24 hours causes osmotic demyelination syndrome 1, 2
• Inadequate monitoring during active correction 1
• Using fluid restriction in CSW worsens outcomes 1
• Failing to recognize and treat underlying cause 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant 4
• Administering hypotonic fluids (lactated Ringer's, 0.45% saline, D5W) in any hyponatremia—they worsen the condition 1

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Monitoring Protocol

During active correction: 1

• Severe symptoms: Serum sodium every 2 hours
• After symptom resolution: Every 4-6 hours
• Chronic asymptomatic: Every 24-48 hours initially

Track: Daily weights, fluid balance, neurologic exam, electrolytes (potassium, magnesium), renal function 1