What is the appropriate acute management for a patient presenting with presyncope and severe hyponatremia (serum sodium 115 mmol/L)?

Acute Management of Severe Hyponatremia with Presyncope

This patient requires immediate administration of 3% hypertonic saline to prevent life-threatening complications, as a sodium level of 115 mmol/L with presyncope represents severe symptomatic hyponatremia that constitutes a medical emergency. 1

Immediate Emergency Treatment

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 The initial goal is to correct sodium by 6 mmol/L over the first 6 hours or until severe symptoms resolve—this rapid initial correction is critical to prevent seizures, coma, or death. 1, 2

• Start 3% hypertonic saline immediately without waiting for additional workup 1, 2
• Target correction: 6 mmol/L in first 6 hours 1, 3
• Critical safety limit: total correction must not exceed 8 mmol/L in any 24-hour period 1, 4
• After the initial 6 mmol/L correction, only 2 mmol/L additional correction is permitted in the remaining 18 hours 3

Intensive Monitoring Protocol

Check serum sodium every 2 hours during the initial correction phase to ensure you stay within safe limits and avoid osmotic demyelination syndrome. 1, 3

• Monitor for resolution of presyncope and other neurological symptoms 3
• Once severe symptoms resolve, transition to checking sodium every 4 hours 3
• Admit to ICU for close monitoring during active correction 1

Determining Volume Status and Underlying Cause

While treatment should not be delayed, rapidly assess volume status to guide subsequent management after the emergency phase:

Physical examination for volume status (though sensitivity is only 41% and specificity 80%): 1

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins
• Euvolemic signs: normal blood pressure, no edema, normal skin turgor
• Hypervolemic signs: peripheral edema, ascites, jugular venous distention

Obtain urine sodium and osmolality to differentiate causes: 1

• Urine sodium <30 mmol/L suggests hypovolemic hyponatremia (71-100% positive predictive value for saline responsiveness) 1
• Urine sodium >20-40 mmol/L with urine osmolality >300 mOsm/kg suggests SIADH 1
• Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 1

Transition After Symptom Resolution

Once presyncope and severe symptoms resolve, discontinue 3% saline and transition to management based on the underlying cause: 3

For SIADH (euvolemic): 1

• Implement fluid restriction to 1 L/day
• Add oral sodium chloride 100 mEq three times daily if no response to fluid restriction
• Continue monitoring sodium every 4 hours initially, then daily

For hypovolemic hyponatremia: 1

• Switch to isotonic saline (0.9% NaCl) for volume repletion
• Initial rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response
• Discontinue any diuretics

For hypervolemic hyponatremia (heart failure, cirrhosis): 1

• Implement fluid restriction to 1-1.5 L/day
• Temporarily discontinue diuretics if sodium <125 mmol/L
• Consider albumin infusion in cirrhotic patients

Critical Safety Considerations

The single most important principle: never exceed 8 mmol/L correction in 24 hours. 1, 4 Overcorrection causes osmotic demyelination syndrome, which manifests 2-7 days later with dysarthria, dysphagia, oculomotor dysfunction, and quadriparesis—a devastating and potentially irreversible complication. 1

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

• Advanced liver disease
• Chronic alcoholism
• Malnutrition
• Prior hepatic encephalopathy
• Severe hyponatremia (<120 mmol/L)

Management of Overcorrection

If sodium rises too rapidly (>8 mmol/L in 24 hours), immediately: 1

• Stop all hypertonic saline
• Switch to D5W (5% dextrose in water) to relower sodium
• Consider administering desmopressin to slow or reverse the rapid rise
• Target: bring total 24-hour correction back to ≤8 mmol/L from baseline

Common Pitfalls to Avoid

• Never delay treatment while pursuing a diagnosis—severe symptomatic hyponatremia is a medical emergency requiring immediate hypertonic saline 5, 2
• Never aim for normonatremia acutely—the therapeutic goal is 125-130 mmol/L, not normal range 6
• Never use fluid restriction as initial treatment for severe symptomatic hyponatremia—this requires hypertonic saline 1, 3
• Never ignore mild chronic hyponatremia (130-135 mmol/L) as clinically insignificant—it increases mortality 60-fold and significantly increases fall risk 7
• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—studies show no neurologic complications when correction stays below 12 mmol/L per 24 hours or 18 mmol/L per 48 hours 4