How should hyponatremia be evaluated and managed based on severity, duration, and volume status?

Evaluation and Management of Hyponatremia

Initial Assessment Framework

Hyponatremia requires immediate evaluation when serum sodium falls below 135 mmol/L, with full diagnostic workup indicated at <131 mmol/L. 1

The diagnostic approach centers on three critical determinations:

• Severity classification: Mild (130-135 mmol/L), moderate (120-129 mmol/L), or severe (<120 mmol/L) 2
• Duration: Acute (<48 hours) versus chronic (>48 hours), which fundamentally alters treatment approach and correction rates 1, 3
• Volume status: Hypovolemic, euvolemic, or hypervolemic—this determines the underlying mechanism and guides therapy 1

Essential Laboratory Workup

Obtain these tests before initiating treatment 1:

• Serum and urine osmolality
• Urine sodium concentration
• Urine electrolytes
• Serum uric acid (values <4 mg/dL suggest SIADH with 73-100% positive predictive value) 1
• Thyroid-stimulating hormone (to exclude hypothyroidism) 1
• Serum creatinine and BUN (assess renal function) 1

Do not delay treatment while awaiting ADH or natriuretic peptide levels—these tests lack clinical utility and are not supported by evidence. 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

For patients with seizures, coma, altered consciousness, or respiratory distress, immediately administer 3% hypertonic saline regardless of the serum sodium level. 1, 2, 4

Dosing protocol: 1

• Give 100 mL boluses of 3% NaCl IV over 10 minutes
• Repeat up to three times at 10-minute intervals
• Target: Increase sodium by 6 mmol/L over 6 hours OR until severe symptoms resolve
• Critical safety limit: Never exceed 8 mmol/L correction in 24 hours

Monitoring during acute correction: 1

• Check serum sodium every 2 hours during initial correction
• ICU admission required for close monitoring
• Switch to every 4 hours after symptom resolution

Moderate Symptoms (Nausea, Vomiting, Confusion, Headache)

Treatment depends on volume status and underlying cause, but correction remains cautious 1:

• Maximum correction: 8 mmol/L in 24 hours
• For high-risk patients (cirrhosis, alcoholism, malnutrition): limit to 4-6 mmol/L per day 1

Asymptomatic or Mild Symptoms

Even mild chronic hyponatremia (130-135 mmol/L) is not benign—it increases fall risk 21% versus 5% in normonatremic patients and carries a 60-fold increased mortality risk when sodium <130 mmol/L. 5, 4

Treatment focuses on addressing the underlying cause rather than rapid correction 1, 2.

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Clinical signs: Orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1

Diagnostic clue: Urine sodium <30 mmol/L predicts 71-100% response to saline infusion 1

Treatment: 1

• Discontinue diuretics immediately
• Administer isotonic saline (0.9% NaCl) for volume repletion
• Initial rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response
• For cirrhotic patients: Consider albumin infusion alongside saline, with maximum correction 4-6 mmol/L per day 1

Euvolemic Hyponatremia (SIADH)

Diagnostic criteria: 1

• Euvolemic on exam (no edema, no orthostatic hypotension)
• Urine osmolality >300 mOsm/kg despite low serum osmolality
• Urine sodium >20-40 mmol/L
• Normal thyroid, adrenal, and renal function

Treatment algorithm: 1, 2

1. First-line: Fluid restriction to 1 L/day (or <800 mL/day for refractory cases)
2. If no response: Add oral sodium chloride 100 mEq three times daily
3. For resistant cases: Consider vasopressin receptor antagonists (tolvaptan 15 mg daily, titrate to 30-60 mg) or urea 1, 4
4. Severe symptoms: 3% hypertonic saline with target correction 6 mmol/L over 6 hours

Common pitfall: In neurosurgical patients, distinguish SIADH from cerebral salt wasting (CSW)—they require opposite treatments. CSW presents with true hypovolemia and requires volume/sodium replacement, NOT fluid restriction. 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Clinical signs: Peripheral edema, ascites, jugular venous distention 1

Treatment for sodium <125 mmol/L: 1

• Fluid restriction to 1-1.5 L/day
• Temporarily discontinue diuretics until sodium improves
• For cirrhotic patients: Consider albumin infusion (8 g per liter of ascites removed)
• Avoid hypertonic saline unless life-threatening symptoms present—it worsens edema and ascites 1

Critical principle: In cirrhosis, sodium restriction (not fluid restriction) drives weight loss, as fluid passively follows sodium 1

Critical Safety Considerations

Osmotic Demyelination Syndrome Prevention

The single most important safety principle: Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours. 1, 4

High-risk populations requiring even slower correction (4-6 mmol/L per day): 1

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

If overcorrection occurs: 1

• Immediately discontinue current fluids
• Switch to D5W (5% dextrose in water)
• Consider desmopressin to slow or reverse the rapid rise
• Target: bring total 24-hour correction back to ≤8 mmol/L from baseline

Signs of osmotic demyelination (appear 2-7 days after rapid correction): 1

• Dysarthria, dysphagia
• Oculomotor dysfunction
• Quadriparesis

Special Population Considerations

Neurosurgical patients with subarachnoid hemorrhage: 1

• Never use fluid restriction in patients at risk for vasospasm—it worsens outcomes
• Consider fludrocortisone 0.1-0.2 mg daily to prevent vasospasm
• Hydrocortisone may prevent natriuresis

Cirrhotic patients: 1

• Hyponatremia increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36)
• Maximum correction: 4-6 mmol/L per day, absolute ceiling 8 mmol/L in 24 hours
• Risk of osmotic demyelination: 0.5-1.5% even with careful correction

Common Pitfalls to Avoid

• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—it increases mortality and fall risk 1, 5
• Using fluid restriction in cerebral salt wasting—this is fatal; CSW requires volume replacement 1
• Inadequate monitoring during active correction—check sodium every 2 hours initially for severe symptoms 1
• Failing to recognize the underlying cause—review medications (SSRIs, carbamazepine, NSAIDs, diuretics) 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—it worsens fluid overload 1
• Overly rapid correction exceeding 8 mmol/L in 24 hours—this causes osmotic demyelination syndrome 1, 4