Hyponatremia Medication Dosing
For severe symptomatic hyponatremia (seizures, altered mental status, coma), immediately administer 3% hypertonic saline as 100-150 mL IV boluses to increase serum sodium by 4-6 mmol/L within 1-2 hours, but limit total correction to 8 mmol/L in the first 24 hours to prevent osmotic demyelination syndrome. 1, 2
Acute Severe/Symptomatic Hyponatremia
Hypertonic Saline (3% NaCl) Dosing
Initial Management:
- Bolus approach (preferred): 100-150 mL IV bolus of 3% saline over 10 minutes 2, 3
- Alternative continuous infusion: 1-2 mL/kg/hour for 2-3 hours 4
- Target: Increase serum sodium by 4-6 mmol/L within first 1-2 hours to reverse cerebral edema 1, 2
Calculation of sodium deficit:
- Na deficit (mEq) = Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1
Critical Correction Limits:
- First 24 hours: Maximum 8-10 mmol/L 1, 2
- 48 hours: Maximum 18 mmol/L 1, 5
- Never exceed: 10-12 mmol/L per 24 hours to avoid osmotic demyelination 1, 5
Monitoring:
- Check serum sodium every 2 hours during acute correction 1
- Monitor urine output closely for unexpected water diuresis 6, 5
Preventing Overcorrection
Desmopressin protocol:
- Administer desmopressin 1-2 mcg IV/SC every 6-8 hours concurrently with hypertonic saline 6
- This prevents unpredictable water diuresis and allows controlled, predictable correction 6
- If overcorrection occurs, give desmopressin immediately to terminate water diuresis 5
Chronic/Asymptomatic Hyponatremia
SIADH (Euvolemic)
First-line:
Second-line (for non-responders to fluid restriction):
Oral urea:
Vaptans (vasopressin receptor antagonists):
- Reserved for recurrent/refractory cases 7, 2
- Caution: Risk of overly rapid correction; requires close monitoring 2, 8
Oral sodium chloride:
- 100 mEq (salt tablets) three times daily if no response to fluid restriction 1
Cerebral Salt Wasting (Hypovolemic)
Severe symptoms:
- 3% hypertonic saline (same dosing as above) PLUS
- Fludrocortisone: 0.1 mg three times daily for 7 days 1
- Normal saline IV fluids for volume repletion 1
Mild symptoms or asymptomatic:
- Normal saline IV fluids 1
- Oral sodium chloride 100 mEq three times daily 1
- Monitor daily weights and intake/output 1
Alternative corticosteroid:
- Hydrocortisone 1200 mg/day to prevent natriuresis (particularly in SAH patients) 1
Hypervolemic Hyponatremia (Cirrhosis/Heart Failure)
Outpatient management:
- Sodium restriction AND water restriction (1-1.5 L/day) 7
- Modify or discontinue diuretics 7
- Increase laxatives to promote solute-free water loss 7
Inpatient management:
- Continue sodium and water restriction 7
- IV albumin 20-25% (6-8 g per liter of ascites removed if >5L) 7
- Consider oral vasoconstrictors (midodrine) 7
Refractory cases:
- Vaptans (tolvaptan) 7, 2
- IV vasoconstrictor therapy 7
- Hypertonic saline (only if severely symptomatic) 7
- TIPS referral for appropriate candidates 7
Special Populations
Subarachnoid Hemorrhage (SAH)
- Treat even mild hyponatremia (Na 131-135 mmol/L) 1
- Never use fluid restriction - increases risk of cerebral infarction 1
- Maintain hypervolemia for vasospasm prevention 1
Neurosurgical Patients
- Threshold for treatment: Na <131 mmol/L 1
- Check sodium every 4 hours for mild symptoms, every 2 hours for severe 1
Critical Pitfalls to Avoid
Overcorrection is the most dangerous complication - causes permanent neurological damage from osmotic demyelination 1, 2, 9
Unexpected water diuresis - most common cause of inadvertent overcorrection; prevented by concurrent desmopressin 6, 5
Fluid restriction in CSW or SAH - worsens outcomes and increases cerebral infarction risk 1
Rapid correction of chronic hyponatremia - brain has adapted; rapid correction causes more harm than the hyponatremia itself 1
Inadequate monitoring - serum sodium must be checked frequently (every 2-4 hours initially) during active correction 1, 5