Management of Hyponatremia with Sodium 128 mEq/L
For a patient with sodium 128 mEq/L, implement fluid restriction to 1-1.5 L/day if hypervolemic or euvolemic, or administer isotonic saline if hypovolemic, while ensuring correction does not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1
Initial Assessment
Determine volume status immediately by examining for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemic); peripheral edema, ascites, jugular venous distention (hypervolemic); or absence of these findings (euvolemic). 1 Physical examination alone has limited accuracy (sensitivity 41%, specificity 80%), so supplement with laboratory data. 1
Obtain essential laboratory tests:
- Serum and urine osmolality 1
- Urine sodium concentration 1
- Urine electrolytes 1
- Serum uric acid (levels <4 mg/dL suggest SIADH with 73-100% positive predictive value) 1
- Assess extracellular fluid volume status 1
Check for symptoms: At sodium 128 mEq/L, patients may experience nausea, vomiting, weakness, headache, mild confusion, or lack of concentration. 2, 3 This level represents moderate hyponatremia requiring treatment. 1, 2
Treatment Based on Volume Status
Hypovolemic Hyponatremia
Administer isotonic saline (0.9% NaCl) for volume repletion. 1 Urine sodium <30 mmol/L predicts good response to saline infusion (positive predictive value 71-100%). 1 Discontinue diuretics if contributing to hyponatremia. 1
Euvolemic Hyponatremia (SIADH)
Implement fluid restriction to 1 L/day as first-line treatment. 1, 4 If no response to fluid restriction after 24-48 hours, add oral sodium chloride 100 mEq three times daily. 1 For resistant cases, consider urea or vasopressin receptor antagonists (tolvaptan 15 mg once daily). 1, 4
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day. 1 Temporarily discontinue diuretics if sodium remains <125 mmol/L. 1 For cirrhotic patients, consider albumin infusion alongside fluid restriction. 1 Avoid hypertonic saline unless life-threatening symptoms develop, as it worsens ascites and edema. 1
Correction Rate Guidelines
Maximum correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1, 2, 4 Target correction rate of 4-6 mmol/L per day is safer for most patients. 1
Monitor serum sodium:
Special Populations Requiring Slower Correction (4-6 mmol/L per day)
Patients at higher risk for osmotic demyelination syndrome include those with: 1
- Advanced liver disease
- Alcoholism
- Malnutrition
- Prior encephalopathy
- Severe hyponatremia (<120 mmol/L)
Pharmacological Options
Vasopressin receptor antagonists (vaptans) can increase serum sodium significantly in euvolemic or hypervolemic hyponatremia, with effects seen as early as 8 hours after first dose. 5, 4 Tolvaptan starting dose is 15 mg once daily, titrated to 30-60 mg based on response. 1, 5 Use with caution due to risk of overly rapid correction and increased thirst. 4 In cirrhotic patients, tolvaptan carries higher risk of gastrointestinal bleeding (10% vs 2% placebo). 1
Critical Pitfalls to Avoid
- Never ignore mild hyponatremia (130-135 mmol/L) as it increases fall risk (21% vs 5% in normonatremic patients) and mortality (60-fold increase). 1, 4
- Never exceed 8 mmol/L correction in 24 hours - overcorrection causes osmotic demyelination syndrome with dysarthria, dysphagia, oculomotor dysfunction, or quadriparesis appearing 2-7 days later. 1, 6
- Never use fluid restriction in cerebral salt wasting - this worsens outcomes in neurosurgical patients. 1
- Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms. 1
If Overcorrection Occurs
Immediately discontinue current fluids and switch to D5W (5% dextrose in water). 1 Consider administering desmopressin to slow or reverse rapid sodium rise. 1, 6 Target relowering to bring total 24-hour correction to no more than 8 mmol/L from baseline. 1