How should a patient with a serum sodium of 115 mEq/L be evaluated and treated?

Management of Serum Sodium 115 mEq/L

A patient with serum sodium of 115 mEq/L requires immediate assessment of symptom severity and volume status, followed by urgent treatment with 3% hypertonic saline if symptomatic or careful correction with isotonic fluids if asymptomatic, never exceeding 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome.

Immediate Assessment

Determine symptom severity first—this dictates urgency of intervention:

• Severe symptoms (seizures, coma, altered mental status, confusion) require immediate 3% hypertonic saline regardless of chronicity 1, 2
• Moderate symptoms (nausea, vomiting, headache, weakness) warrant hospital admission with monitored correction 2, 3
• Asymptomatic patients can be managed more conservatively based on underlying cause 1, 2

Assess volume status through physical examination:

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
• Euvolemic: normal volume status, no edema, normal blood pressure 1
• Hypervolemic signs: peripheral edema, ascites, jugular venous distention 1

Obtain critical laboratory workup:

• Serum and urine osmolality 1, 2
• Urine sodium concentration 1, 2
• Serum creatinine, glucose, thyroid function 4, 3

Treatment Based on Symptom Severity

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

Administer 3% hypertonic saline immediately:

• Give 100 mL boluses over 10 minutes, repeating up to three times at 10-minute intervals 1
• Target correction of 6 mmol/L over first 6 hours or until symptoms resolve 1, 2
• Absolute maximum: 8 mmol/L in any 24-hour period 1, 2, 5, 6
• Check serum sodium every 2 hours during active correction 1, 2
• Admit to ICU for close monitoring 1, 2

Asymptomatic or Mildly Symptomatic

Treatment depends on volume status:

Hypovolemic hyponatremia:

• Administer isotonic saline (0.9% NaCl) for volume repletion 1, 3
• Initial rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
• Discontinue diuretics immediately 1

Euvolemic hyponatremia (SIADH):

• Fluid restriction to 1 L/day as first-line treatment 1, 2
• Add oral sodium chloride 100 mEq three times daily if no response to fluid restriction 1
• Consider vasopressin receptor antagonists (tolvaptan 15 mg daily) for resistant cases 1

Hypervolemic hyponatremia (heart failure, cirrhosis):

• Fluid restriction to 1-1.5 L/day 1, 2
• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• Consider albumin infusion in cirrhotic patients 1
• Avoid hypertonic saline unless life-threatening symptoms present 1

Critical Correction Rate Guidelines

Standard correction limits for all patients:

• Maximum 8 mmol/L in any 24-hour period 1, 2, 5, 6
• Target rate: 4-8 mmol/L per day 1
• Do not exceed 10-12 mmol/L in 24 hours under any circumstances 1, 6

High-risk patients require even slower correction (4-6 mmol/L per day maximum):

• Advanced liver disease 1, 2
• Chronic alcoholism 1, 2
• Malnutrition 1, 2
• Serum sodium <115 mEq/L 7
• Prior hepatic encephalopathy 1

For patients with sodium <115 mEq/L specifically:

• Limit correction to <8 mmol/L in 24 hours due to exceptionally high risk of osmotic demyelination 7
• Consider thiamine supplementation (500 mg IV three times daily) before any glucose-containing fluids 7

Special Considerations for Neurosurgical Patients

Distinguish SIADH from cerebral salt wasting (CSW)—they require opposite treatments:

SIADH characteristics:

• Euvolemic state 1, 2
• Urine sodium >20-40 mmol/L 1
• Urine osmolality >300 mOsm/kg 1
• Treatment: fluid restriction 1, 2

Cerebral salt wasting characteristics:

• True hypovolemia with CVP <6 cm H₂O 1, 2
• Urine sodium >20 mmol/L despite volume depletion 1
• Clinical signs: orthostatic hypotension, tachycardia, dry mucous membranes 1
• Treatment: volume and sodium replacement with isotonic or hypertonic saline 1, 2
• Add fludrocortisone 0.1-0.2 mg daily for severe symptoms 1, 2
• Never use fluid restriction—this worsens outcomes 1, 2

Monitoring Protocol

During active correction:

• Check serum sodium every 2 hours for severe symptoms 1, 2
• Check every 4 hours after symptom resolution 1
• Continue daily monitoring for at least 7-10 days 2

Watch for signs of osmotic demyelination syndrome (typically 2-7 days after correction):

• Dysarthria, dysphagia 1
• Oculomotor dysfunction 1
• Quadriparesis 1
• Altered mental status 1

Management of Overcorrection

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

• Immediately discontinue current fluids 1
• Switch to D5W (5% dextrose in water) 1
• Consider administering desmopressin to slow or reverse the rapid rise 1
• Target: bring total 24-hour correction back to ≤8 mmol/L from baseline 1

Common Pitfalls to Avoid

• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—this causes osmotic demyelination syndrome 1, 2, 5, 6
• Never use fluid restriction in cerebral salt wasting—this worsens outcomes and can precipitate cerebral ischemia 1, 2
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—this worsens edema and ascites 1
• Never fail to identify high-risk patients (liver disease, alcoholism, malnutrition, sodium <115 mEq/L) who require slower correction 1, 2, 7
• Never delay treatment while pursuing a complete diagnostic workup—treat based on symptom severity first 3