Management of Hyponatremia
Initial Assessment and Classification
Hyponatremia management is fundamentally determined by three critical factors: symptom severity, duration of onset (acute <48 hours vs chronic >48 hours), and volume status (hypovolemic, euvolemic, or hypervolemic). 1
The initial workup must include:
- Serum and urine osmolality 1
- Urine sodium concentration 1
- Uric acid level 1
- Assessment of extracellular fluid volume status through physical examination 1
Volume status assessment should identify:
- Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
- Euvolemic signs: absence of edema, normal blood pressure, normal skin turgor 1
- Hypervolemic signs: peripheral edema, ascites, jugular venous distention 1
Treatment Based on Symptom Severity
Severe Symptomatic Hyponatremia (Seizures, Coma, Altered Mental Status)
For patients with severe neurological symptoms, immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over the first 6 hours or until symptoms resolve. 1
- Administer 3% hypertonic saline as 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals 1
- Monitor serum sodium every 2 hours during initial correction 1
- The absolute maximum correction is 8 mmol/L in any 24-hour period to prevent osmotic demyelination syndrome 1
- Consider ICU admission for close monitoring 1
Mild to Moderate Symptomatic or Asymptomatic Hyponatremia
Treatment depends on volume status and underlying etiology rather than immediate hypertonic saline 1
Treatment Based on Volume Status
Hypovolemic Hyponatremia
Discontinue diuretics immediately and administer isotonic saline (0.9% NaCl) for volume repletion. 1
- Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
- Urine sodium <30 mmol/L predicts good response to saline (positive predictive value 71-100%) 1
- For severe dehydration with neurological symptoms, consider hypertonic saline with careful monitoring 1
- Maximum correction: 8 mmol/L in 24 hours 1
Euvolemic Hyponatremia (SIADH)
Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1
- If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
- For severe symptoms: 3% hypertonic saline with careful monitoring 1
- Pharmacological options for resistant cases:
Critical distinction: In neurosurgical patients, cerebral salt wasting (CSW) must be differentiated from SIADH 1:
- CSW: Treat with volume and sodium replacement (isotonic or hypertonic saline), NOT fluid restriction 1
- CSW with severe symptoms: 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily in ICU 1
- Never use fluid restriction in CSW as it worsens outcomes 1
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L. 1
- Discontinue diuretics temporarily if sodium <125 mmol/L 1
- For cirrhotic patients: consider albumin infusion (8 g per liter of ascites removed) 1
- Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens ascites and edema 1
- Sodium restriction (2-2.5 g/day) is more effective than fluid restriction for weight loss, as fluid follows sodium 1
- Vasopressin receptor antagonists may be considered for persistent severe hyponatremia despite fluid restriction and maximization of guideline-directed medical therapy 1
Critical Correction Rate Guidelines
The single most important safety principle is never exceeding 8 mmol/L correction in 24 hours. 1
Standard-Risk Patients
High-Risk Patients (Advanced Liver Disease, Alcoholism, Malnutrition, Prior Encephalopathy)
- Target: 4-6 mmol/L per day 1
- Absolute maximum: 8 mmol/L in 24 hours 1
- Risk of osmotic demyelination syndrome: 0.5-1.5% even with careful correction 1
Acute vs Chronic Hyponatremia
- Acute (<48 hours): Can be corrected more rapidly without risk of osmotic demyelination 1
- Chronic (>48 hours): Requires slower correction; maximum 1 mmol/L/hour only for severely symptomatic cases 1
Management of Overcorrection
If sodium correction exceeds 8 mmol/L in 24 hours, immediately intervene to prevent osmotic demyelination syndrome. 1
- Discontinue current fluids and switch to D5W (5% dextrose in water) 1
- Consider administering desmopressin to slow or reverse the rapid rise 1
- Target: bring total 24-hour correction back to ≤8 mmol/L from baseline 1
- Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1
Special Population Considerations
Cirrhotic Patients
- 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: 4-6 mmol/L per day maximum 1
- Albumin infusion should be tried before tolvaptan 1
- Tolvaptan carries higher risk of gastrointestinal bleeding in cirrhosis (10% vs 2% placebo) 1
- Use tolvaptan only for ≤30 days with monthly liver function monitoring 1
Neurosurgical Patients
- Cerebral salt wasting is more common than SIADH in this population 1
- Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1
- Consider fludrocortisone 0.1-0.2 mg daily to prevent vasospasm 1
- Hydrocortisone may be used to prevent natriuresis 1
Patients with Renal Failure
- For hypovolemic hyponatremia with elevated creatinine: isotonic saline for volume repletion 1
- Continuous venovenous hemofiltration (CVVH) with low-sodium replacement fluid may be necessary for controlled correction 1
- Limit correction to 4-6 mEq/L per day in high-risk patients with renal impairment 1
Common Pitfalls to Avoid
- Overly rapid correction exceeding 8 mmol/L in 24 hours leading to osmotic demyelination syndrome 1
- Inadequate monitoring during active correction 1
- Using fluid restriction in cerebral salt wasting, which worsens outcomes 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, particularly in high-risk populations 1
- Misdiagnosing volume status, leading to inappropriate treatment 2
- Using normal saline in SIADH, which can worsen hyponatremia 1
Monitoring Requirements
During Active Correction
- Severe symptoms: Check sodium every 2 hours 1
- Mild symptoms: Check sodium every 4 hours 1
- After symptom resolution: Check sodium every 4-6 hours, then daily 1