What is the treatment approach for a hospitalized patient with hyponatremia (low serum sodium level)?

Treatment of Hyponatremia in the Hospital

Hospitalized patients with hyponatremia should be managed based on symptom severity and volume status, with the critical principle that sodium correction must never exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1

Initial Assessment and Classification

Before initiating treatment, perform a rapid but systematic evaluation:

• Measure serum sodium, serum osmolality, urine osmolality, and urine sodium to determine the underlying cause 1
• Assess volume status clinically by examining for orthostatic hypotension, dry mucous membranes, skin turgor (hypovolemic), peripheral edema, ascites, jugular venous distention (hypervolemic), or absence of these findings (euvolemic) 1
• Determine symptom severity: severe symptoms include altered mental status, seizures, or coma; mild symptoms include nausea, headache, or confusion 1, 2
• Establish chronicity: acute (<48 hours) versus chronic (>48 hours), as this affects correction rate safety 1

Physical examination alone has poor accuracy for volume assessment (sensitivity 41%, specificity 80%), so laboratory values are essential 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

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

• Administer 3% hypertonic saline as 100 mL boluses over 10 minutes, which can be repeated up to three times at 10-minute intervals until symptoms improve 1
• Target correction: 6 mmol/L in the first 6 hours, then stop aggressive correction 1
• Absolute maximum: 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2
• Monitor serum sodium every 2 hours during initial correction 1
• ICU admission is recommended for close monitoring during treatment 1

The initial infusion rate can be estimated by: body weight (kg) × desired rate of increase in sodium (mmol/L per hour) 3

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends on volume status and underlying cause:

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Administer isotonic saline (0.9% NaCl) for volume repletion at an initial rate of 15-20 mL/kg/h, then 4-14 mL/kg/h based on clinical response 1

• Discontinue diuretics immediately if sodium <125 mmol/L 1
• Urine sodium <30 mmol/L predicts good response to saline infusion (positive predictive value 71-100%) 1
• Maximum correction: 8 mmol/L in 24 hours even with volume repletion 1
• Consider albumin infusion in cirrhotic patients alongside isotonic saline 1

Euvolemic Hyponatremia (SIADH)

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

• Implement strict fluid restriction to 1000 mL/day as first-line therapy 1
• Add oral sodium chloride 100 mEq three times daily if no response to fluid restriction alone 1
• For severe symptoms, use 3% hypertonic saline with target correction of 6 mmol/L over 6 hours 1
• Consider vasopressin receptor antagonists (tolvaptan 15 mg once daily) for resistant cases, starting at 15 mg and titrating to 30-60 mg as needed 1, 4
• Avoid fluid restriction during the first 24 hours when initiating tolvaptan to prevent overly rapid correction 4

Alternative pharmacological options include urea, demeclocycline, or lithium, though these are less commonly used 1

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L. 1

• Fluid restriction to 1000-1500 mL/day is the primary intervention 1
• Temporarily discontinue diuretics if sodium <125 mmol/L 1
• In cirrhotic patients, consider albumin infusion (8 g per liter of ascites removed) alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens edema and ascites 1
• Vasopressin receptor antagonists may be considered for persistent severe hyponatremia despite fluid restriction and maximization of guideline-directed medical therapy 1, 4

Note that it is sodium restriction, not fluid restriction, that results in weight loss in cirrhotic patients, as fluid passively follows sodium 1

Critical Correction Rate Guidelines

The maximum correction rate must not exceed 8 mmol/L in 24 hours for most patients. 1, 2

• Standard correction rate: 4-8 mmol/L per day, not exceeding 10-12 mmol/L in 24 hours 1
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1
• For severe symptoms: 6 mmol/L in first 6 hours, then slow correction to stay within 8 mmol/L total in 24 hours 1

Overly rapid correction (>12 mmol/L in 24 hours) can cause osmotic demyelination syndrome, resulting in dysarthria, dysphagia, lethargy, spastic quadriparesis, seizures, coma, or death 4, 5

Special Considerations for Neurosurgical Patients

In neurosurgical patients, distinguish between SIADH and cerebral salt wasting (CSW), as they require opposite treatments. 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 (CVP <6 cm H₂O), urine sodium >20 mmol/L despite volume depletion, clinical signs of volume depletion; treat with volume and sodium replacement, NOT fluid restriction 1
• For CSW with severe symptoms: administer 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily in ICU 1
• In subarachnoid hemorrhage patients at risk of vasospasm: never use fluid restriction; consider fludrocortisone or hydrocortisone to prevent natriuresis 1

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours:

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Consider administering desmopressin (1-2 µg parenterally every 6-8 hours) to slow or reverse the rapid rise 1, 6
• Target relowering to bring total 24-hour correction to no more than 8 mmol/L from starting point 1

Monitoring During Treatment

• Severe symptoms: check serum sodium every 2 hours during initial correction 1
• Mild symptoms: check serum sodium every 4 hours initially, then daily 1
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Common Pitfalls to Avoid

• Never use fluid restriction as initial treatment for severe symptomatic hyponatremia with altered mental status—this is a medical emergency requiring hypertonic saline 1
• Never exceed 8 mmol/L correction in 24 hours—overcorrection risks osmotic demyelination syndrome 1, 2
• Never use fluid restriction in cerebral salt wasting—this worsens outcomes 1
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—it worsens fluid overload 1
• Inadequate monitoring during active correction is a common pitfall 1
• Failing to recognize and treat the underlying cause leads to recurrence 1
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—even mild hyponatremia increases fall risk and mortality 1, 2