How to correct hyponatremia in patients with varying severity and underlying causes, including those with symptoms like seizures or severe hyponatremic encephalopathy, and those with conditions like Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) or heart failure?

Correcting Hyponatremia

For severe symptomatic hyponatremia (seizures, altered mental status, coma), immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until symptoms resolve, never exceeding 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1

Initial Assessment

Before initiating treatment, rapidly determine three critical factors:

• Symptom severity: Severe symptoms (seizures, coma, altered consciousness) versus mild symptoms (nausea, headache, weakness) versus asymptomatic 1, 2
• Volume status: Assess for hypovolemia (orthostatic hypotension, dry mucous membranes, decreased skin turgor), euvolemia (normal examination), or hypervolemia (edema, ascites, jugular venous distension) 1
• Acuity: Acute (<48 hours) versus chronic (>48 hours) onset, as acute hyponatremia causes more severe symptoms at the same sodium level 1, 2

Obtain serum and urine osmolality, urine sodium, and urine electrolytes to determine the underlying cause 1. A urine sodium <30 mmol/L predicts response to saline with 71-100% positive predictive value 1.

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

For patients with seizures, coma, confusion, or altered consciousness:

• Administer 3% hypertonic saline immediately as 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1, 3
• Target correction: 6 mmol/L increase over first 6 hours or until severe symptoms resolve 1
• Maximum correction limit: Never exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 3, 4
• Monitor serum sodium every 2 hours during initial correction phase 1
• ICU admission required for close monitoring during treatment 1

The correction formula is: Sodium deficit = Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1.

Mild to Moderate Symptomatic or Asymptomatic Hyponatremia

Treatment depends on volume status:

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics immediately if sodium <125 mmol/L 1. Administer isotonic saline (0.9% NaCl) for volume repletion:

• Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
• Continue until euvolemia achieved, monitoring for improvement in sodium levels 1
• Avoid hypotonic fluids (lactated Ringer's, 0.45% saline, D5W) as these worsen hyponatremia 1

For severe dehydration with neurological symptoms, consider hypertonic saline with careful monitoring 1.

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment 1, 3, 5:

• Implement strict fluid restriction as first-line therapy 1
• If no response after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1
• For persistent cases despite fluid restriction, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1, 6
• Alternative pharmacological options include urea, demeclocycline, or lithium for resistant cases 1, 3

For severe symptomatic SIADH, use 3% hypertonic saline as described above, then transition to fluid restriction once symptoms resolve 1.

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 5, 7:

• Temporarily discontinue diuretics if sodium <125 mmol/L 1
• For cirrhotic patients: Consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens edema and ascites 1
• Sodium restriction (2-2.5 g/day) is more effective than fluid restriction for weight loss, as fluid follows sodium 1

For persistent severe hyponatremia despite fluid restriction and maximized guideline-directed therapy, consider vasopressin antagonists (tolvaptan) in the short term 1, 6. However, use extreme caution in cirrhosis due to higher risk of gastrointestinal bleeding (10% vs 2% placebo) 1.

Special Populations Requiring Cautious Correction

High-risk patients require slower correction rates of 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 3:

• Advanced liver disease or cirrhosis 1
• Chronic alcoholism 1
• Malnutrition 1
• Prior encephalopathy 1
• Severe hyponatremia (<120 mmol/L) 1

These patients have significantly higher risk of osmotic demyelination syndrome 1, 8.

Neurosurgical Patients: Critical Distinction

Distinguish between SIADH and cerebral salt wasting (CSW), as they require opposite treatments 1:

SIADH characteristics:

• Euvolemic state (normal CVP) 1
• Urine sodium >20-40 mmol/L 1
• Urine osmolality >300 mOsm/kg 1
• Treatment: Fluid restriction to 1 L/day 1

Cerebral Salt Wasting characteristics:

• True hypovolemia (CVP <6 cm H₂O) 1
• Urine sodium >20 mmol/L despite volume depletion 1
• Clinical signs of volume depletion 1
• Treatment: Volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1

For severe CSW symptoms, administer 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily in ICU 1. Never use fluid restriction in CSW as this worsens outcomes 1.

For subarachnoid hemorrhage patients at risk of vasospasm, never use fluid restriction and consider fludrocortisone or hydrocortisone to prevent natriuresis 1.

Critical Safety Considerations

Preventing Osmotic Demyelination Syndrome

The single most important principle: Never exceed 8 mmol/L correction in 24 hours 1, 3, 4, 8:

• For average-risk patients: 4-8 mmol/L per day, maximum 10-12 mmol/L in 24 hours 1
• For high-risk patients: 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1
• Overly rapid correction can cause osmotic demyelination syndrome, presenting with dysarthria, dysphagia, oculomotor dysfunction, quadriparesis, or locked-in syndrome 2-7 days after rapid correction 1, 8

Managing Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours 1:

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Consider administering desmopressin to slow or reverse the rapid rise 1
• Target relowering to bring total 24-hour correction to no more than 8 mmol/L from starting point 1

Monitoring Requirements

• Severe symptoms: Check serum sodium every 2 hours during initial correction 1
• Mild symptoms: Check every 4 hours after symptom resolution 1
• Chronic correction: Monitor daily to ensure correction does not exceed 8 mmol/L in 24 hours 1
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Common Pitfalls to Avoid

• Never ignore mild hyponatremia (130-135 mmol/L) as it increases fall risk (21% vs 5%), mortality (60-fold increase with sodium <130 mmol/L), and cognitive impairment 1, 2, 3
• Never use fluid restriction as initial treatment for altered mental status from hyponatremia—this is a medical emergency requiring hypertonic saline 1
• Never use fluid restriction in cerebral salt wasting—this worsens outcomes 1
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—it worsens edema and ascites 1
• Never fail to monitor adequately during active correction—inadequate monitoring leads to overcorrection 1
• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—this causes osmotic demyelination syndrome 1, 8