What is the treatment for an adult patient with hyponatremia, particularly those with euvolemic or hypervolemic hyponatremia, severe hyponatremia, or underlying conditions such as heart failure or liver disease?

Treatment of Hyponatremia

Immediate Assessment: Determine Symptom Severity and Volume Status

For severe symptomatic hyponatremia (seizures, coma, altered mental status), immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until symptoms resolve—this is a medical emergency. 1

The first critical step is determining symptom severity and volume status through physical examination:

• Severe symptoms requiring immediate intervention include seizures, coma, confusion, obtundation, or cardiorespiratory distress 1, 2
• Mild symptoms include nausea, vomiting, headache, weakness, or mild neurocognitive deficits 2, 3
• Volume status assessment requires checking for orthostatic hypotension, dry mucous membranes, skin turgor (hypovolemic); peripheral edema, ascites, jugular venous distention (hypervolemic); or absence of these findings (euvolemic) 1

Obtain initial workup including serum and urine osmolality, urine sodium, urine electrolytes, serum uric acid, and assessment of extracellular fluid volume status 1

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Critical Correction Rate Guidelines: The Single Most Important Safety Principle

Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome—this limit is absolute and non-negotiable. 1, 2, 4

• For average-risk patients: aim for 4-8 mmol/L per day, maximum 10-12 mmol/L in 24 hours 1
• For high-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): limit to 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 5
• Monitor serum sodium every 2 hours during initial correction for severe symptoms, every 4 hours after symptom resolution 1

If overcorrection occurs, immediately discontinue current fluids, switch to D5W (5% dextrose in water), and consider desmopressin to slow or reverse the rapid rise 1, 6

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Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion. 1, 3

• Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
• Urine sodium <30 mmol/L predicts good response to saline infusion (positive predictive value 71-100%) 1
• For severe dehydration with neurological symptoms, consider hypertonic saline with careful monitoring 1, 5
• 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 for SIADH. 1, 3

• For mild/asymptomatic cases: fluid restriction <1 L/day as first-line 1, 2
• If no response to fluid restriction: add oral sodium chloride 100 mEq three times daily 1
• For severe symptomatic cases: 3% hypertonic saline with careful monitoring 1
• Pharmacological options for resistant cases: vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg), demeclocycline, or urea 1, 2

Serum uric acid <4 mg/dL has a positive predictive value of 73-100% for SIADH 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L and avoid hypertonic saline unless life-threatening symptoms are present. 1, 3

• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• For cirrhotic patients: consider albumin infusion alongside fluid restriction 1, 5
• Avoid hypertonic saline as it may worsen ascites and edema 1, 5
• Vasopressin receptor antagonists may be considered for persistent severe hyponatremia despite fluid restriction and maximization of guideline-directed medical therapy 1

Important caveat: In cirrhosis, it is sodium restriction (not fluid restriction) that results in weight loss, as fluid passively follows sodium 1

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Special Populations and Critical Considerations

Patients with Liver Disease

Cirrhotic patients require even more cautious correction (4-6 mmol/L per day) due to higher risk of osmotic demyelination syndrome. 1, 5

• Hyponatremia in cirrhosis increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• Tolvaptan carries higher risk of gastrointestinal bleeding in cirrhosis (10% vs 2% placebo) 1
• Albumin infusion can help improve serum sodium levels in cirrhotic patients 1, 5

Neurosurgical Patients: Distinguishing SIADH from Cerebral Salt Wasting

In neurosurgical patients, cerebral salt wasting (CSW) is more common than SIADH and requires fundamentally different treatment—volume and sodium replacement, NOT fluid restriction. 1

• SIADH characteristics: euvolemic state, urine sodium >20-40 mmol/L, urine osmolality >300 mOsm/kg; treat with fluid restriction 1
• CSW characteristics: true hypovolemia with CVP <6 cm H₂O, urine sodium >20 mmol/L despite volume depletion, evidence of extracellular volume depletion; treat with volume and sodium replacement 1
• For severe CSW symptoms: 3% hypertonic saline plus fludrocortisone (0.1-0.2 mg daily) in ICU 1
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm—this worsens outcomes 1

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Common Pitfalls to Avoid

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