How is hyponatremia (low sodium levels) managed and corrected?

Management and Correction of Hyponatremia

Hyponatremia management depends critically on symptom severity and volume status, with correction rates strictly limited to prevent osmotic demyelination syndrome—never exceed 8 mmol/L in 24 hours for most patients, and only 4-6 mmol/L per day in high-risk populations.

Initial Assessment and Classification

Hyponatremia is defined as serum sodium <135 mmol/L and warrants full investigation when <131 mmol/L 1. The initial workup must include:

• Serum and urine osmolality to confirm hypotonic hyponatremia 1
• Urine sodium concentration (spot urine sodium <30 mmol/L predicts 71-100% response to saline; >20 mmol/L with high urine osmolality suggests SIADH) 1, 2
• Serum uric acid (<4 mg/dL has 73-100% positive predictive value for SIADH or cerebral salt wasting) 1
• Extracellular fluid volume status through physical examination (orthostatic hypotension, skin turgor, edema, ascites, jugular venous distention) 1, 3

Severity classification: Mild (130-135 mmol/L), moderate (125-129 mmol/L), severe (<125 mmol/L) 1, 3. Even mild hyponatremia increases fall risk (21% vs 5% in normonatremic patients) and mortality (60-fold increase with sodium <130 mmol/L) 1, 2.

Emergency Management: Severe Symptomatic Hyponatremia

For patients with severe symptoms (seizures, coma, confusion, obtundation, cardiorespiratory distress), immediately administer 3% hypertonic saline 1, 4, 2:

• Initial bolus: 100 mL of 3% saline IV over 10 minutes 4, 3
• Repeat boluses: Can repeat every 10 minutes up to three times if symptoms persist 4
• Target correction: Increase sodium by 4-6 mmol/L over the first 1-2 hours OR until symptoms resolve 1, 4, 2
• 24-hour limit: Maximum 8 mmol/L total correction in 24 hours (10 mmol/L absolute maximum per some guidelines, but 8 mmol/L is safer) 1, 4, 2

Monitoring during acute correction:

• Check serum sodium every 2 hours during initial correction phase 1, 4
• After symptom resolution, check every 4 hours 1
• Monitor strict intake/output and daily weights 4

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Characterized by: True volume depletion, orthostatic hypotension, dry mucous membranes, urine sodium typically <30 mmol/L 1, 3

Treatment approach:

• Discontinue diuretics immediately 1
• Administer isotonic (0.9%) saline for volume repletion 1, 3, 5
• Correction rate still limited to 8 mmol/L per 24 hours 1
• Once euvolemic, reassess if sodium normalizes with volume alone 1

Euvolemic Hyponatremia (SIADH)

Diagnostic criteria: Hypotonic hyponatremia with inappropriately concentrated urine (>100 mOsm/kg), urine sodium >20-40 mmol/L, euvolemic state (no edema, normal blood pressure, normal skin turgor) 1, 5

Treatment hierarchy:

1. Fluid restriction to 1 L/day is the cornerstone of treatment 1, 4, 3
2. If no response: Add oral sodium chloride 100 mEq three times daily 1
3. Pharmacological options for resistant cases:
   • Urea (40 g in 100-150 mL normal saline every 8 hours) 1
   • Vaptans (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1, 6, 2
   • Demeclocycline or lithium (less commonly used due to side effects) 1

Important distinction: In neurosurgical patients, cerebral salt wasting (CSW) is more common than SIADH 1, 4. CSW requires volume and sodium replacement, NOT fluid restriction 1, 4. Distinguishing features of CSW include evidence of volume depletion (hypotension, tachycardia) despite high urine sodium 1.

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Pathophysiology: Non-osmotic vasopressin hypersecretion, enhanced proximal sodium reabsorption, impaired free water clearance 1

Treatment approach:

• Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 3, 7
• Temporarily discontinue diuretics if sodium <125 mmol/L 1
• For cirrhosis: Consider albumin infusion (6-8 g per liter of ascites drained) 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 important than fluid restriction for weight loss, as fluid follows sodium 1

Vaptans in hypervolemic hyponatremia: Tolvaptan may be considered for persistent severe hyponatremia despite fluid restriction and maximized medical therapy 1, 6. However, in cirrhosis, tolvaptan carries higher risk of gastrointestinal bleeding (10% vs 2% placebo) 1, 6.

Calculating Sodium Deficit and Correction

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

Initial 3% saline infusion rate: Body weight (kg) × desired rate of increase (mmol/L per hour) = mL/kg per hour 5

Example: For a 70 kg patient wanting 1 mmol/L/hour increase: 70 × 1 = 70 mL/hour of 3% saline 5

Critical Correction Rate Guidelines

Standard patients: Maximum 8 mmol/L in 24 hours 1, 4, 2, 3

High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy, severe hyponatremia, hypokalemia): Maximum 4-6 mmol/L per day 1, 4

Chronic hyponatremia (>48 hours): Never correct faster than 1 mmol/L/hour 1

If 6 mmol/L corrected in first 6 hours: Limit to only 2 mmol/L in following 18 hours to avoid exceeding 8 mmol/L total 4

Management of Overcorrection

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

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Consider desmopressin to slow or reverse the rapid rise 1
• Target relowering to bring total 24-hour correction to ≤8 mmol/L from starting point 1

Watch for osmotic demyelination syndrome (typically 2-7 days post-correction): dysarthria, dysphagia, oculomotor dysfunction, quadriparesis, parkinsonism 1, 2. Risk is 0.5-1.5% in liver transplant recipients 1.

Special Populations and Considerations

Neurosurgical patients with subarachnoid hemorrhage:

• Never use fluid restriction in patients at risk for vasospasm 1, 4
• Consider fludrocortisone or hydrocortisone to prevent natriuresis 1, 4
• Distinguish CSW from SIADH—CSW requires aggressive volume resuscitation 1

Cirrhotic patients:

• Hyponatremia ≤130 mmol/L increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
• More cautious correction rates (4-6 mmol/L per day) mandatory 1

Patients on diuretics with mild hyponatremia (126-135 mmol/L):

• Can continue diuretics with close electrolyte monitoring if sodium >126 mmol/L and normal creatinine 1
• Stop diuretics if sodium ≤120 mmol/L 1

Common Pitfalls to Avoid

• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—it increases falls and mortality 1, 2
• Using fluid restriction in cerebral salt wasting—this worsens outcomes 1, 4
• Administering hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—worsens fluid overload 1
• Inadequate monitoring during active correction—check sodium every 2 hours initially 1, 4
• Failing to identify and treat underlying cause—leads to recurrence 1
• Overly rapid correction exceeding 8 mmol/L in 24 hours—causes osmotic demyelination syndrome 1, 4, 2