Initial Approach to Treating Hyponatremia
The initial approach to treating hyponatremia must be guided by three critical factors: symptom severity, volume status (hypovolemic, euvolemic, or hypervolemic), and the rate of correction needed to prevent osmotic demyelination syndrome. 1
Immediate Assessment
Determine symptom severity first, as this dictates urgency of treatment:
- Severe symptoms (seizures, coma, altered mental status, cardiorespiratory distress) require immediate intervention with 3% hypertonic saline 1, 2
- Mild symptoms (nausea, headache, confusion) or asymptomatic cases allow for more measured approaches 1
- Symptom severity depends on rapidity of onset—acute hyponatremia (<48 hours) causes more severe symptoms than chronic 1, 3
Assess volume status through physical examination:
- Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, tachycardia 1
- Euvolemic signs: absence of edema, normal blood pressure, normal skin turgor 1
- Hypervolemic signs: peripheral edema, ascites, jugular venous distention, pulmonary congestion 1
Obtain essential laboratory tests:
Treatment Based on Symptom Severity
Severe Symptomatic Hyponatremia (Medical Emergency)
Administer 3% hypertonic saline immediately with the following parameters 1, 2:
- Initial goal: Increase sodium by 6 mmol/L over 6 hours or until severe symptoms resolve 1
- Bolus dosing: 100 mL of 3% saline over 10 minutes, can repeat up to 3 times at 10-minute intervals 1
- Maximum correction: Do not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2
- Monitoring: Check serum sodium every 2 hours during initial correction 1
Asymptomatic or Mildly Symptomatic Hyponatremia
Treatment depends on volume status:
For Hypovolemic Hyponatremia:
- Discontinue diuretics immediately 1
- Administer isotonic saline (0.9% NaCl) for volume repletion 1
- Urine sodium <30 mmol/L predicts response to saline with 71-100% positive predictive value 1
For Euvolemic Hyponatremia (SIADH):
- Fluid restriction to 1 L/day is the cornerstone of treatment 1, 2
- If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
- Consider vasopressin receptor antagonists (tolvaptan 15 mg once daily) for resistant cases 1, 4
For Hypervolemic Hyponatremia (heart failure, cirrhosis):
- Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
- Discontinue diuretics temporarily if sodium <125 mmol/L 1
- Consider albumin infusion in cirrhotic patients 1
- Avoid hypertonic saline unless life-threatening symptoms present, as it worsens edema and ascites 1
Critical Correction Rate Guidelines
Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 2, 3
High-risk patients require even slower correction (4-6 mmol/L per day):
- Advanced liver disease 1
- Alcoholism 1
- Malnutrition 1
- Prior encephalopathy 1
- Severe hyponatremia (<120 mmol/L) 1
Common Pitfalls to Avoid
- Overly rapid correction exceeding 8 mmol/L in 24 hours leads to osmotic demyelination syndrome 1
- Using fluid restriction in cerebral salt wasting (common in neurosurgical patients) worsens outcomes—these patients need volume and sodium replacement 1
- Inadequate monitoring during active correction 1
- Failing to recognize the underlying cause 1
- Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
- Ignoring mild hyponatremia (130-135 mmol/L)—even mild hyponatremia increases fall risk (21% vs 5%) and mortality (60-fold increase at <130 mmol/L) 1, 2
Special Considerations for Neurosurgical Patients
Distinguish between SIADH and cerebral salt wasting (CSW), as treatment differs fundamentally 1, 5: