Management of Hyponatremia
Initial Assessment and Classification
The management of hyponatremia must be guided by three critical factors: symptom severity, volume status (hypovolemic, euvolemic, or hypervolemic), and chronicity (acute <48 hours vs. chronic >48 hours). 1
Initial workup should include:
- Serum and urine osmolality 1
- Urine sodium concentration 1
- Urine electrolytes 1
- Serum uric acid 1
- Assessment of extracellular fluid volume status (checking for orthostatic hypotension, dry mucous membranes, skin turgor, jugular venous distention, peripheral edema, ascites) 1
Hyponatremia severity classification: 1
- Mild: 130-135 mEq/L
- Moderate: 120-125 mEq/L
- Severe: <120 mEq/L
Treatment Based on Symptom Severity
Severe Symptomatic Hyponatremia (Medical Emergency)
For patients with severe symptoms (seizures, coma, confusion, obtundation, cardiorespiratory distress), immediately administer 3% hypertonic saline with a goal to correct sodium by 6 mmol/L over 6 hours or until symptoms resolve. 1
- Administer 3% hypertonic saline as 100 mL boluses over 10 minutes, which can be repeated up to three times at 10-minute intervals until symptoms improve 1
- Maximum correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1
- Monitor serum sodium every 2 hours during initial correction 1
- Consider ICU admission for close monitoring 1
Asymptomatic or Mildly Symptomatic Hyponatremia
Treatment depends on volume status (see below). 1
Treatment Based on Volume Status
Hypovolemic Hyponatremia
For hypovolemic hyponatremia, discontinue diuretics and administer isotonic saline (0.9% NaCl) for volume repletion. 1
- Urinary sodium <30 mmol/L has a positive predictive value of 71-100% for response to 0.9% saline infusion 1
- Once euvolemic, reassess and adjust treatment based on sodium levels 1
- Avoid exceeding correction of 8 mmol/L in 24 hours 1
Euvolemic Hyponatremia (SIADH)
For SIADH, fluid restriction to 1 L/day is the cornerstone of first-line treatment. 1
- If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
- For resistant cases, consider second-line therapies: 1
Important distinction: In neurosurgical patients, cerebral salt wasting (CSW) is more common than SIADH and requires fundamentally different treatment - volume and sodium replacement, NOT fluid restriction. 1
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
For hypervolemic hyponatremia with sodium <125 mmol/L, implement fluid restriction to 1-1.5 L/day. 1
- Discontinue diuretics temporarily if sodium <125 mmol/L 1
- For cirrhotic patients, consider albumin infusion alongside fluid restriction 1
- Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen ascites and edema 1
- Sodium restriction (not just fluid restriction) is more important for weight loss, as fluid passively follows sodium 1
For cirrhotic patients specifically:
- Tolvaptan carries a higher risk of gastrointestinal bleeding (10% vs. 2% placebo) 3
- Hyponatremia in cirrhosis increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1
Correction Rate Guidelines - Critical Safety Parameters
The single most important safety principle: Never exceed correction of 8 mmol/L in 24 hours for most patients. 1
- For severe symptoms: correct 6 mmol/L over 6 hours or until symptoms resolve, then slow correction 1
- For chronic hyponatremia: aim for 4-6 mmol/L per day 1
- For high-risk patients (advanced liver disease, alcoholism, malnutrition, severe hyponatremia, prior encephalopathy): limit to 4-6 mmol/L per day 1
Managing Overcorrection
If overcorrection occurs (>8 mmol/L in 24 hours): 1
- Immediately discontinue current fluids and switch to D5W (5% dextrose in water)
- Consider administering desmopressin to slow or reverse the rapid rise
- Target reduction to bring total 24-hour correction to no more than 8 mmol/L from starting point
Monitoring Requirements
- Severe symptoms: Monitor serum sodium every 2 hours during initial correction 1
- After resolution of severe symptoms: Monitor every 4 hours 1
- Chronic hyponatremia: Monitor daily to ensure correction does not exceed 8 mmol/L in 24 hours 1
- Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1
Common Pitfalls to Avoid
- Overly rapid correction exceeding 8 mmol/L in 24 hours leading to osmotic demyelination syndrome 1
- Using fluid restriction in cerebral salt wasting (CSW), which worsens outcomes 1
- Inadequate monitoring during active correction 1
- Failing to recognize and treat the underlying cause 1
- Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
- Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant - even mild hyponatremia increases fall risk (21% vs. 5%) and mortality 1, 4
Special Populations
Neurosurgical Patients
- Distinguish between SIADH and cerebral salt wasting (CSW) - treatment approaches differ fundamentally 1
- CSW requires volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1
- Consider fludrocortisone for hyponatremia in subarachnoid hemorrhage patients at risk of vasospasm 1
- Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1