What are the steps for sodium replacement in patients with hyponatremia?

Sodium Replacement in Hyponatremia

For severe symptomatic hyponatremia (seizures, coma, altered mental status), immediately administer 3% hypertonic saline as 100-150 mL IV bolus over 10 minutes, repeatable up to three times at 10-minute intervals, targeting a 6 mmol/L increase over 6 hours or until symptoms resolve—never exceeding 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome. 1, 2, 3, 4

Initial Assessment and Classification

Before initiating sodium replacement, rapidly determine three critical factors 1:

• Volume status: Assess for orthostatic hypotension, dry mucous membranes, skin turgor (hypovolemic); jugular venous distention, peripheral edema, ascites (hypervolemic); or absence of both (euvolemic) 1, 4
• Symptom severity: Severe symptoms include seizures, coma, confusion, obtundation, cardiorespiratory distress; mild symptoms include nausea, vomiting, headache, weakness 1, 3, 4
• Chronicity: Acute (<48 hours) versus chronic (>48 hours)—this distinction is critical as chronic hyponatremia requires slower correction rates 1, 5

Obtain serum and urine osmolality, urine sodium, and uric acid immediately 1. A urine sodium <30 mmol/L predicts 71-100% response to normal saline, while >20 mmol/L with high urine osmolality (>500 mOsm/kg) suggests SIADH 1, 3.

Treatment Algorithm Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

Administer 3% hypertonic saline immediately 1, 2, 3, 4:

• Bolus method (preferred): Give 100-150 mL IV bolus over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1, 6
• Continuous infusion alternative: Calculate initial rate as body weight (kg) × desired sodium increase (1-2 mmol/L/hour) 7
• Target: Increase sodium by 6 mmol/L over first 6 hours or until severe symptoms resolve 1, 2
• Absolute limit: Never exceed 8 mmol/L correction in 24 hours 1, 2, 3, 4

Monitor serum sodium every 2 hours during initial correction 1. Once severe symptoms resolve, discontinue 3% saline and transition to protocols for mild symptoms 2. After initial 6 mmol/L correction, limit additional correction to only 2 mmol/L in the following 18 hours 2.

Mild Symptomatic or Asymptomatic Hyponatremia

Treatment depends on volume status 1, 3, 4:

Hypovolemic hyponatremia 1, 3:

• Discontinue diuretics immediately 1
• Administer isotonic (0.9%) saline for volume repletion 1, 3
• Correction rate: 4-8 mmol/L per day, not exceeding 8 mmol/L in 24 hours 1

Euvolemic hyponatremia (SIADH) 1, 3, 4:

• First-line: Fluid restriction to 1 L/day 1, 3, 4
• If no response: Add oral sodium chloride 100 mEq three times daily 1
• Second-line options: Urea (effective and safe) 1, 4, 6, vaptans (tolvaptan 15 mg daily, titrate to 30-60 mg) 1, 8, 4, or demeclocycline/lithium (less commonly used due to side effects) 1

Hypervolemic hyponatremia (heart failure, cirrhosis) 1, 3, 4:

• Primary treatment: Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 3
• Cirrhosis patients: Consider albumin infusion alongside fluid restriction 1, 4
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens edema and ascites 1
• Vaptans: May be considered for persistent severe hyponatremia despite fluid restriction and maximization of guideline-directed therapy 1, 8

Correction Rate Guidelines and High-Risk Populations

Standard correction rates 1, 4, 6:

• Average risk patients: 4-8 mmol/L per day, maximum 10-12 mmol/L in 24 hours 1
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 3, 4

Acute hyponatremia (<48 hours)** can be corrected more rapidly (1-2 mmol/L/hour) without risk of osmotic demyelination syndrome 1, 2. **Chronic hyponatremia (>48 hours) requires slower correction after initial symptom control 2, 6.

Special Considerations for Neurosurgical Patients

In neurosurgical patients, cerebral salt wasting (CSW) is more common than SIADH and requires fundamentally different treatment 1, 4:

CSW treatment 1:

• Volume and sodium replacement with isotonic or hypertonic saline (NOT fluid restriction) 1
• For severe symptoms: 3% hypertonic saline plus fludrocortisone in ICU 1
• Hydrocortisone may prevent natriuresis in subarachnoid hemorrhage patients 1
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1, 2

Managing Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours 1, 4:

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

Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1, 3, 4.

Monitoring During Treatment

Severe symptoms: Monitor serum sodium every 2 hours during initial correction 1. After severe symptoms resolve, monitor every 4 hours 1, 2.

Mild symptoms or asymptomatic: Monitor daily initially, then every 4 hours after resolution of symptoms 1.

Continue treatment until sodium reaches 131 mmol/L (exception: subarachnoid hemorrhage patients receive treatment even for sodium 131-135 mmol/L) 2.

Critical Pitfalls to Avoid

• Overly rapid correction exceeding 8 mmol/L in 24 hours causes osmotic demyelination syndrome 1, 3, 4
• Using fluid restriction in CSW worsens outcomes 1, 2
• Inadequate monitoring during active correction 1
• Ignoring mild hyponatremia (130-135 mmol/L) increases fall risk (21% vs 5%) and mortality (60-fold increase when <130 mmol/L) 1, 4
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms worsens fluid overload 1
• Failing to calculate corrected sodium in hyperglycemia: Add 1.6 mEq/L for every 100 mg/dL glucose above 100 mg/dL to avoid inappropriate fluid selection 9