How should I acutely manage an unarousable adult with severe hyponatraemia (serum sodium 115 mmol/L) and blood urea nitrogen 11 mmol/L?

Acute Management of Severe Hyponatremia with Altered Mental Status

Administer 100 mL of 3% hypertonic saline intravenously over 10 minutes immediately, repeating every 10 minutes up to three total boluses if the patient remains unarousable, with a target correction of 6 mmol/L over the first 6 hours. 1, 2

Immediate Emergency Intervention

This patient presents with severe symptomatic hyponatremia (sodium 115 mmol/L) and altered consciousness—a life-threatening medical emergency requiring urgent hypertonic saline, not fluid restriction. 1, 2, 3

First-Line Treatment Protocol

• Give 100 mL boluses of 3% NaCl IV over 10 minutes, repeating at 10-minute intervals (maximum three boluses) until neurological symptoms improve 1, 2, 4
• Target an initial increase of 4-6 mmol/L in the first hour to reverse cerebral edema and restore consciousness 2, 4, 5
• Aim for 6 mmol/L correction over 6 hours or until the patient becomes arousable, whichever comes first 1, 2, 4

The BUN of 11 mmol/L (approximately 31 mg/dL) suggests possible volume depletion, making hypertonic saline even more appropriate as initial therapy. 1

Critical Correction Rate Limits

The absolute maximum correction is 8 mmol/L in any 24-hour period to prevent osmotic demyelination syndrome. 1, 2, 3, 4

Calculating Safe Correction

• If you achieve 6 mmol/L correction in the first 6 hours, allow only 2 mmol/L additional rise in the remaining 18 hours 1, 2
• Never aim for normonatremia acutely—the therapeutic goal is 125-130 mmol/L, not normal range 1, 5
• For patients with liver disease, alcoholism, or malnutrition, limit correction to 4-6 mmol/L per day maximum 1, 2

Intensive Monitoring Requirements

Laboratory Surveillance

• Check serum sodium every 2 hours during the initial correction phase 1, 2, 4
• After symptoms resolve, continue checking every 4 hours until stable 1, 2
• Monitor for signs of overcorrection throughout the first 24-48 hours 2, 3

Clinical Assessment

• Strict intake-output monitoring to track fluid balance 2
• Serial neurological examinations to assess mental status improvement 2, 3
• Watch for osmotic demyelination syndrome signs (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically appearing 2-7 days after rapid correction 1, 2

Determining the Underlying Cause

While treating the emergency, simultaneously assess:

• Volume status: Look for orthostatic hypotension, dry mucous membranes, skin turgor, jugular venous distention, peripheral edema 1, 2
• Urine studies: Obtain urine sodium and osmolality to distinguish SIADH from cerebral salt wasting or hypovolemic causes 1, 2
• Serum osmolality and uric acid: Serum uric acid <4 mg/dL suggests SIADH with 73-100% positive predictive value 1

The elevated BUN with severe hyponatremia raises concern for hypovolemic hyponatremia (from vomiting, diarrhea, diuretics) or cerebral salt wasting if there is CNS pathology. 1

Post-Acute Management Based on Etiology

If SIADH (Euvolemic)

• Implement fluid restriction to 1 L/day once symptoms resolve 1, 2
• Add oral sodium chloride 100 mEq three times daily if fluid restriction fails 1, 2
• Consider urea (0.5-1 g/kg/day) for resistant cases 1, 6

If Cerebral Salt Wasting (Hypovolemic)

• Continue volume and sodium replacement with isotonic or hypertonic saline—never use fluid restriction 1, 2
• Add fludrocortisone 0.1-0.2 mg daily for severe symptoms or subarachnoid hemorrhage patients 1, 2
• Target central venous pressure 8-12 cm H₂O to confirm adequate volume repletion 1

If 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 response 1
• Discontinue any diuretics immediately 1

Management of Overcorrection

If sodium rises >8 mmol/L in 24 hours:

• Immediately stop hypertonic saline and switch to D5W (5% dextrose in water) 1, 3, 4
• Administer desmopressin to slow or reverse the rapid rise 1, 3, 4
• Target relowering to bring total 24-hour correction back to ≤8 mmol/L from baseline 1

Critical Pitfalls to Avoid

• Never use fluid restriction as initial treatment for an unarousable patient—this is a hypertonic saline emergency 1, 2
• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—overcorrection causes irreversible osmotic demyelination 1, 2, 3, 4
• Never use fluid restriction in cerebral salt wasting—it worsens outcomes and can precipitate cerebral ischemia 1, 2
• Never delay treatment while awaiting ADH or natriuretic peptide levels—evidence does not support this delay 1

Why This Approach Prioritizes Outcomes

Severe symptomatic hyponatremia with altered consciousness carries 60-fold increased mortality risk (11.2% vs 0.19%) if untreated. 7 Immediate hypertonic saline reverses life-threatening cerebral edema within hours, while careful rate control prevents osmotic demyelination syndrome—the balance between these two neurological threats defines optimal management. 8, 3, 4, 5