How to evaluate and treat hyponatremia?

Evaluation and Treatment of Hyponatremia

Initial Evaluation

Begin evaluation when serum sodium is <135 mmol/L, but active treatment should be initiated when sodium falls below 131 mmol/L. 1

Essential Laboratory Workup

• Measure serum osmolality to rule out pseudohyponatremia (normal: 275-290 mOsm/kg) 1
• Obtain urine osmolality and urine sodium concentration to determine the underlying mechanism 1, 2
• Check serum uric acid - levels <4 mg/dL have 73-100% positive predictive value for SIADH (though may also occur in cerebral salt wasting) 1, 2
• Assess thyroid function (TSH) and cortisol to exclude hypothyroidism and adrenal insufficiency 1
• Do NOT routinely measure ADH or natriuretic peptide levels - this is not supported by evidence and delays treatment 1

Volume Status Assessment

Physical examination alone is inadequate for determining volume status (sensitivity 41%, specificity 80%). 2 Look for:

• Hypovolemia: orthostatic hypotension, dry mucous membranes, decreased skin turgor, tachycardia 3, 1
• Euvolemia: absence of edema, normal blood pressure, moist mucous membranes 2
• Hypervolemia: jugular venous distention, peripheral edema, ascites, orthopnea 1

Urine sodium <30 mmol/L predicts response to normal saline with 71-100% positive predictive value. 1, 2

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Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Seizures, Coma, Altered Mental Status)

Administer 3% hypertonic saline immediately with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve. 1, 4

• Give 100-150 mL boluses of 3% saline over 10 minutes, repeatable up to 3 times at 10-minute intervals 1, 5
• Maximum correction: 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 3, 1, 6
• Monitor serum sodium every 2 hours during initial correction 1
• Requires ICU admission for close monitoring 1

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends on volume status:

Hypovolemic Hyponatremia

• Discontinue diuretics immediately 1
• Administer isotonic (0.9%) saline for volume repletion 1
• Correction rate: 4-8 mmol/L per day, not exceeding 8 mmol/L in 24 hours 1

Euvolemic Hyponatremia (SIADH)

• Fluid restriction to 1 L/day is the cornerstone of treatment 3, 1
• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
• Second-line options: urea (40 g every 8 hours), demeclocycline, lithium, or loop diuretics 3, 1, 5
• Tolvaptan 15 mg daily (titrate to 30-60 mg) for resistant cases, but requires hospital initiation and monitoring 6

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

• Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• In cirrhosis, consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present 1
• Sodium restriction (not fluid restriction) produces weight loss, as fluid follows sodium 1

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Special Populations and Considerations

Neurosurgical Patients: SIADH vs. Cerebral Salt Wasting (CSW)

Distinguishing between these conditions is critical as treatments are opposite. 3, 1

Cerebral Salt Wasting:

• Treat with volume and sodium replacement, NOT fluid restriction 3, 1
• For severe symptoms: 3% hypertonic saline plus fludrocortisone in ICU 3, 1
• Hydrocortisone may prevent natriuresis in subarachnoid hemorrhage patients 3, 1
• Never use fluid restriction in SAH patients at risk of vasospasm 3, 1

High-Risk Patients (Advanced Liver Disease, Alcoholism, Malnutrition)

These patients require more cautious correction at 4-6 mmol/L per day due to higher risk of osmotic demyelination syndrome. 1, 6

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Critical Correction Rate Guidelines

The maximum safe correction rate is 8 mmol/L in 24 hours. 3, 1, 6 Exceeding this risks osmotic demyelination syndrome, which manifests 2-7 days after rapid correction with dysarthria, dysphagia, oculomotor dysfunction, and quadriparesis. 1

If overcorrection occurs:

• Immediately discontinue current fluids and switch to D5W 1
• Consider desmopressin to slow or reverse the rapid rise 1

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Common Pitfalls to Avoid

• Ignoring mild hyponatremia (130-135 mmol/L) - even mild hyponatremia increases fall risk and mortality 1, 4
• Using fluid restriction in cerebral salt wasting - this worsens outcomes 3, 1
• Inadequate monitoring during active correction - check sodium every 2-4 hours initially 1
• Failing to recognize the underlying cause - treatment must address etiology 3, 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms - this worsens edema and ascites 1
• Relying solely on physical examination for volume status determination - use laboratory parameters 2

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Monitoring During Treatment

• Severe symptoms: monitor sodium every 2 hours during initial correction 1
• After symptom resolution: monitor every 4 hours, then daily 1
• Watch for osmotic demyelination syndrome signs (typically 2-7 days post-correction): dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 1
• After discontinuing tolvaptan, resume fluid restriction and monitor sodium levels 6