Hyponatremia Management
Initial Assessment and Classification
Confirm true hyponatremia by checking serum osmolality (<275 mOsm/kg) and exclude pseudohyponatremia from hyperglycemia (correct sodium by adding 1.6 mEq/L for each 100 mg/dL glucose >100 mg/dL). 1 Obtain serum and urine osmolality, urine sodium, and urine electrolytes to determine the underlying cause 2. Assess volume status through physical examination looking for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemia), or peripheral edema, ascites, and jugular venous distention (hypervolemia) 2, 1.
Classify hyponatremia by severity:
Treatment Based on Symptom Severity
Severe Symptomatic Hyponatremia (Seizures, Coma, Altered Mental Status)
This is a medical emergency requiring immediate 3% hypertonic saline administration. 2, 1 Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1. Target correction of 6 mmol/L over the first 6 hours or until severe symptoms resolve 2, 1. Never exceed 8 mmol/L total correction in 24 hours to prevent osmotic demyelination syndrome. 2, 1
Monitor serum sodium every 2 hours during initial correction 2, 1. If overcorrection occurs (>8 mmol/L in 24 hours), immediately discontinue current fluids, switch to D5W (5% dextrose in water), and consider administering desmopressin 2, 1.
Asymptomatic or Mildly Symptomatic Hyponatremia
Treatment depends on volume status and underlying etiology 2, 1.
Treatment Based on Volume Status
Hypovolemic Hyponatremia
Discontinue diuretics immediately and administer isotonic (0.9%) saline for volume repletion. 2, 1 Urine sodium <30 mmol/L predicts good response to saline infusion with 71-100% positive predictive value 2. Continue isotonic fluids until euvolemia is achieved 2.
Euvolemic Hyponatremia (SIADH)
Fluid restriction to 1 L/day is the cornerstone of treatment. 2, 1 If no response to fluid restriction after 24-48 hours, add oral sodium chloride 100 mEq three times daily 2. For persistent cases despite fluid restriction, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrating to 30-60 mg as needed) 2, 3.
Tolvaptan increased serum sodium by 3.7 mEq/L at Day 4 and 4.6 mEq/L at Day 30 compared to placebo in clinical trials 3. However, use with extreme caution and avoid in cirrhotic patients due to 10% risk of gastrointestinal bleeding versus 2% with placebo 2, 3.
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L. 2, 1 Treat the underlying condition aggressively 1. In cirrhotic patients, consider albumin infusion alongside fluid restriction 2, 1. Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens ascites and edema. 2
Temporarily discontinue diuretics if sodium <125 mmol/L 2, 1. For heart failure patients with persistent severe hyponatremia despite fluid restriction and guideline-directed medical therapy, vasopressin antagonists may be considered short-term 2.
Critical Correction Rate Guidelines
Standard correction rate: 4-8 mmol/L per day, never exceeding 8 mmol/L in 24 hours. 2, 1 This limit is absolute to prevent osmotic demyelination syndrome 2, 1, 4, 5.
High-Risk Patients Requiring Slower Correction (4-6 mmol/L per day):
- Advanced liver disease 2, 1
- Alcoholism 2, 1
- Malnutrition 2, 1
- Prior encephalopathy 2, 1
- Severe hyponatremia (<120 mmol/L) 2
These patients have significantly higher risk of osmotic demyelination syndrome and require more cautious management 2, 1.
Management by Sodium Level
Sodium 126-135 mmol/L
Continue current therapy with close electrolyte monitoring 1. No water restriction needed at this level 2. If on diuretics, continue with monitoring 1.
Sodium 121-125 mmol/L
For hypervolemic patients, implement fluid restriction to 1-1.5 L/day 2, 1. Consider temporarily discontinuing diuretics 2. More cautious approach warranted 1.
Sodium ≤120 mmol/L
Stop diuretics immediately. 1 Implement severe fluid restriction plus albumin infusion (for cirrhosis) or volume expansion (for hypovolemia) 1. If symptomatic, use 3% hypertonic saline with careful monitoring 2, 1.
Special Population Considerations
Cirrhotic Patients
Hyponatremia ≤130 mEq/L increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 2. Require correction rate of 4-6 mmol/L per day 2, 1. Albumin infusion should be tried before vaptans 2.
Neurosurgical Patients
Distinguish between SIADH and cerebral salt wasting (CSW) 2. CSW requires volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 2. Consider fludrocortisone for subarachnoid hemorrhage patients at risk of vasospasm 2. Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm. 2
Monitoring Protocol
- Severe symptoms: Check serum sodium every 2 hours during initial correction 2, 1
- Mild symptoms: Check every 4 hours after symptom resolution 2
- Stable patients: Daily monitoring until target sodium achieved 1
Common Pitfalls to Avoid
- Overly rapid correction (>8 mmol/L in 24 hours) causes osmotic demyelination syndrome 2, 1, 5
- Using fluid restriction in cerebral salt wasting worsens outcomes 2
- Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms worsens edema 2
- Inadequate monitoring during active correction 2
- Failing to recognize and treat the underlying cause 2
- Ignoring mild hyponatremia (130-135 mmol/L) which increases fall risk (21% vs 5%) and mortality (60-fold increase) 2, 5