How should I evaluate and treat a patient with a serum sodium of 132 mEq/L?

Evaluation and Management of Serum Sodium 132 mEq/L

Initial Assessment

A serum sodium of 132 mEq/L represents mild hyponatremia that warrants evaluation but typically does not require aggressive intervention unless symptoms are present. 1

Determine Clinical Context

• Assess symptom severity: Mild hyponatremia (130-135 mEq/L) may cause nausea, vomiting, weakness, headache, or mild cognitive deficits, though many patients remain asymptomatic 2, 3
• Establish chronicity: Determine whether onset is acute (<48 hours) or chronic (>48 hours), as acute hyponatremia causes more severe symptoms at the same sodium level 2, 4
• Evaluate volume status: Perform physical examination looking specifically for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemia), or peripheral edema, ascites, jugular venous distention (hypervolemia) 1

Essential Laboratory Workup

Order serum and urine osmolality, urine sodium concentration, serum creatinine, and thyroid-stimulating hormone to determine the underlying cause. 1

• Serum osmolality distinguishes true hypotonic hyponatremia from pseudohyponatremia 1
• Urine osmolality <100 mOsm/kg suggests appropriate ADH suppression; >100 mOsm/kg indicates impaired water excretion 1
• Urine sodium <30 mmol/L suggests hypovolemic hyponatremia with 71-100% positive predictive value for saline responsiveness 1
• Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 1

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Treatment Algorithm Based on Volume Status

For Hypovolemic Hyponatremia (Urine Na <30 mmol/L, signs of volume depletion)

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 contributing to sodium loss 1
• Target correction rate of 4-8 mEq/L per day, never exceeding 8 mEq/L in 24 hours 1
• Monitor serum sodium every 4-6 hours during active correction 1

For Euvolemic Hyponatremia (SIADH suspected)

Implement fluid restriction to 1 L/day as first-line therapy. 1, 5

• If no response to fluid restriction after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1
• Consider vasopressin receptor antagonists (tolvaptan 15 mg once daily) for resistant cases, though this is rarely needed at sodium 132 mEq/L 1, 6
• Avoid fluid restriction in neurosurgical patients where cerebral salt wasting is possible 1

For Hypervolemic Hyponatremia (Heart failure, cirrhosis)

At sodium 132 mEq/L in hypervolemic states, continue current diuretic therapy with close electrolyte monitoring; fluid restriction is not yet indicated. 1

• Fluid restriction to 1-1.5 L/day is reserved for sodium <125 mEq/L 1
• For cirrhotic patients, consider albumin infusion alongside fluid management 1
• Avoid hypertonic saline unless life-threatening symptoms develop 1

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Correction Rate Guidelines and Safety

The absolute maximum correction is 8 mmol/L in any 24-hour period to prevent osmotic demyelination syndrome. 1, 4

• Target 4-6 mEq/L per day for high-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy) 1
• Monitor for signs of osmotic demyelination syndrome 2-7 days after correction: dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 1
• If overcorrection occurs, immediately administer D5W or desmopressin to relower sodium 1

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Special Considerations

Medication Review

Evaluate all medications for potential causes, particularly SSRIs, carbamazepine, NSAIDs, diuretics, and chemotherapy agents. 1, 7

• Drug-induced hyponatremia often resolves with discontinuation and water restriction 7
• Trazodone and other antidepressants place patients at particularly high risk 1

High-Risk Populations

• Cirrhotic patients: Even mild hyponatremia indicates worsening hemodynamic status and increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• Elderly patients: Advanced age is associated with increased risk of hyponatremia and its complications 7
• Neurosurgical patients: Distinguish between SIADH and cerebral salt wasting, as treatments are opposite 1

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Common Pitfalls to Avoid

• Do not ignore mild hyponatremia (130-135 mEq/L) as clinically insignificant—it increases fall risk 4-fold (21% vs 5%) and mortality 60-fold (11.2% vs 0.19%) when sodium <130 mEq/L 1, 2
• Do not apply aggressive fluid restriction at sodium 132 mEq/L unless SIADH is confirmed and symptomatic 1
• Do not use hypertonic saline for asymptomatic mild hyponatremia—reserve for severe symptoms (seizures, coma, altered consciousness) 1, 3
• Do not correct faster than 8 mEq/L in 24 hours regardless of initial sodium level 1, 8