Initial Approach to Treating Hyponatremia
The initial approach to treating hyponatremia must be determined by assessing symptom severity, volume status (hypovolemic, euvolemic, or hypervolemic), and serum osmolality, with immediate hypertonic saline reserved for severe symptomatic cases and fluid restriction or volume repletion for asymptomatic patients based on their volume status. 1
Immediate Assessment Steps
Determine symptom severity first – this dictates urgency of treatment:
- Severe symptoms (seizures, coma, altered mental status, respiratory distress) require immediate intervention 1, 2
- Mild symptoms (nausea, headache, confusion, weakness) allow time for diagnostic workup 2, 3
- Asymptomatic patients can undergo full evaluation before treatment 1, 3
Obtain essential laboratory tests immediately:
- Serum sodium, serum osmolality, urine osmolality, and urine sodium concentration 1, 4
- Serum creatinine, glucose, thyroid function, and cortisol to exclude other causes 1
- Assess extracellular fluid volume status clinically (orthostatic vitals, skin turgor, edema, ascites) 1, 4
Treatment Algorithm Based on Symptom Severity
For Severe Symptomatic Hyponatremia (Medical Emergency)
Administer 3% hypertonic saline immediately with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve 1, 3, 5. This can be given as:
- 100-150 mL boluses over 10 minutes, repeated up to 3 times at 10-minute intervals 5
- Continuous infusion with rate calculated as: body weight (kg) × desired rate of increase (mmol/L/hour) 4
Critical safety limit: Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 3, 5. Monitor serum sodium every 2 hours during initial correction 1.
For Asymptomatic or Mildly Symptomatic Hyponatremia
Treatment depends on volume status:
Hypovolemic hyponatremia (orthostatic hypotension, dry mucous membranes, urine sodium <30 mmol/L):
- Discontinue diuretics immediately 1
- Administer isotonic saline (0.9% NaCl) for volume repletion 1, 4
- Correction rate should not exceed 8 mmol/L in 24 hours 1
Euvolemic hyponatremia (SIADH – normal volume status, urine sodium >20-40 mmol/L, urine osmolality >300 mOsm/kg):
- Fluid restriction to 1 L/day is the cornerstone of treatment 1, 4, 6
- Add oral sodium chloride 100 mEq three times daily if no response to fluid restriction 1
- Consider urea or vaptans (tolvaptan 15 mg daily) for resistant cases 1, 3, 5
Hypervolemic hyponatremia (heart failure, cirrhosis – edema, ascites, jugular venous distention):
- Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1, 4
- Discontinue diuretics temporarily 1
- Consider albumin infusion in cirrhotic patients 1
- Avoid hypertonic saline unless life-threatening symptoms present – it worsens fluid overload 1
High-Risk Populations Requiring Slower Correction
Patients with advanced liver disease, alcoholism, malnutrition, or prior encephalopathy require more cautious correction at 4-6 mmol/L per day (not exceeding 8 mmol/L in 24 hours) due to higher risk of osmotic demyelination syndrome 1, 3.
Special Consideration: Neurosurgical Patients
Distinguish between SIADH and cerebral salt wasting (CSW) – treatment approaches are opposite:
- SIADH: Euvolemic, treat with fluid restriction 1, 6
- CSW: Hypovolemic (low CVP, orthostatic hypotension despite high urine sodium), treat with volume and sodium replacement, NOT fluid restriction 1, 6
- Fludrocortisone may be considered for CSW in subarachnoid hemorrhage patients 1
Common Pitfalls to Avoid
- Never use fluid restriction in hypovolemic states or cerebral salt wasting – this worsens outcomes 1
- Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours – risk of osmotic demyelination syndrome 1, 3, 5
- Never ignore mild hyponatremia (130-135 mmol/L) – it increases fall risk (21% vs 5%) and mortality (60-fold increase) 1, 2, 3
- Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms – it worsens edema and ascites 1
- Inadequate monitoring during active correction leads to overcorrection 1