How should I manage an adult with hyponatremia (serum sodium ≤125 mmol/L) who has mild to moderate symptoms?

Management of Hyponatremia (Serum Sodium ≤125 mmol/L) with Mild to Moderate Symptoms

For an adult with hyponatremia (serum sodium ≤125 mmol/L) and mild to moderate symptoms (nausea, vomiting, headache, confusion, weakness), you should initiate treatment based on volume status while ensuring sodium correction does not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1, 2

Initial Assessment and Volume Status Determination

Your first priority is determining the patient's volume status, as this dictates completely opposite treatment strategies 1:

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

Obtain urine sodium and osmolality immediately—urine sodium <30 mmol/L suggests hypovolemic hyponatremia responsive to saline, while >20 mmol/L with high urine osmolality (>300 mOsm/kg) suggests SIADH 1, 3

Treatment Algorithm Based on Volume Status

For Hypovolemic Hyponatremia

Administer isotonic saline (0.9% NaCl) for volume repletion at 15-20 mL/kg/h initially, then 4-14 mL/kg/h based on clinical response 1. Discontinue any diuretics immediately 1. In cirrhotic patients, consider albumin infusion (8 g per liter of ascites removed) alongside saline, and limit correction to 4-6 mmol/L per day due to higher osmotic demyelination risk 1.

For Euvolemic Hyponatremia (SIADH)

Implement fluid restriction to 1 L/day as first-line therapy 1, 2, 4. If fluid restriction fails after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1. For persistent cases despite these measures, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrated to 30-60 mg) 1, 2, though this requires hospital initiation with sodium monitoring every 2 hours for the first 8 hours 2.

For Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 5, 1, 4. Temporarily discontinue diuretics until sodium improves 5, 1. In cirrhotic patients, consider albumin infusion alongside fluid restriction 1. Avoid hypertonic saline unless life-threatening symptoms develop, as it worsens ascites and edema 1.

Critical Correction Rate Guidelines

The absolute maximum sodium correction is 8 mmol/L in any 24-hour period 1, 2, 4, 3. For standard-risk patients, target 4-8 mmol/L per day 1.

High-risk patients require even slower correction (4-6 mmol/L per day, maximum 8 mmol/L in 24 hours) 1, 2. High-risk features include:

• Advanced liver disease or cirrhosis 1, 2
• Chronic alcoholism 1, 2
• Severe malnutrition 1, 2
• Prior hepatic encephalopathy 1
• Serum sodium <120 mmol/L 1

The FDA label for tolvaptan explicitly warns that "too rapid correction of hyponatremia (e.g., >12 mEq/L/24 hours) can cause osmotic demyelination resulting in dysarthria, mutism, dysphagia, lethargy, affective changes, spastic quadriparesis, seizures, coma and death" 2.

When to Use Hypertonic Saline (3%)

Reserve 3% hypertonic saline only for severe symptomatic hyponatremia (seizures, coma, altered consciousness, respiratory distress) 1, 4, 3. For mild to moderate symptoms (your scenario), hypertonic saline is not indicated 1, 3. If severe symptoms develop, give 100 mL boluses over 10 minutes, repeatable up to three times, targeting 4-6 mmol/L increase over 6 hours or until symptoms resolve 1, 3.

Monitoring Requirements

• Check serum sodium every 4-6 hours during active correction 1
• Monitor for osmotic demyelination syndrome signs (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically appearing 2-7 days after rapid correction 1, 2
• Track daily weights, fluid balance, and clinical volume status 1
• Correct concurrent electrolyte abnormalities (potassium, magnesium) aggressively 1

Common Pitfalls to Avoid

Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—this is the single most important safety principle 1, 2, 4. Even mild chronic hyponatremia (130-135 mmol/L) is associated with 60-fold increased mortality risk and should not be dismissed as clinically insignificant 6, 4.

Do not use fluid restriction in hypovolemic patients—this worsens outcomes 1. Physical examination alone has poor accuracy (sensitivity 41%, specificity 80%) for volume assessment, so incorporate urine studies and clinical context 1.

Avoid hypotonic fluids (0.45% saline, lactated Ringer's, D5W) in any hyponatremic patient, as these worsen the sodium deficit 1, 3.

In cirrhotic patients, sodium restriction (not fluid restriction) drives weight loss, as fluid passively follows sodium 5, 1. Fluid restriction alone rarely improves sodium significantly and compliance is poor 5, 1.

Special Considerations

For neurosurgical patients, distinguish cerebral salt wasting (CSW) from SIADH—CSW requires volume and sodium replacement with isotonic or hypertonic saline plus fludrocortisone 0.1-0.2 mg daily, never fluid restriction 1. In subarachnoid hemorrhage patients at risk for vasospasm, fluid restriction is contraindicated 1.

Mild chronic hyponatremia is not benign—it causes cognitive impairment, gait instability, increased fall risk (23.8% vs 16.4%), and higher fracture rates (23.3% vs 17.3% over 7.4 years) 6, 4. Correction significantly improves cognitive function and quality of life 6.