Hyponatremia Management: Step-by-Step Approach
Initial Assessment and Classification
Begin by confirming true hypotonic hyponatremia with serum osmolality <275 mOsm/kg and exclude pseudohyponatremia from hyperglycemia by adding 1.6 mEq/L to sodium for each 100 mg/dL glucose >100 mg/dL. 1
Determine Acuity and Severity
- Acute hyponatremia is defined as onset <48 hours; **chronic hyponatremia** is >48 hours duration 2
- Severity classification: mild (130-135 mEq/L), moderate (125-129 mEq/L), severe (<125 mEq/L) 3
- Acute hyponatremia causes more severe symptoms than chronic hyponatremia at the same sodium level 4
Assess Volume Status
- Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 2
- Euvolemic signs: normal volume status, no edema, no orthostatic changes 2
- Hypervolemic signs: peripheral edema, ascites, jugular venous distention, pulmonary congestion 2
Essential Laboratory Workup
- Serum and urine osmolality, urine sodium, urine electrolytes 2
- Serum creatinine, thyroid function (TSH), cortisol to exclude endocrine causes 1
- Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 2
Treatment Based on Symptom Severity
Severe Symptomatic Hyponatremia (Medical Emergency)
For patients with confusion, delirium, altered consciousness, seizures, or coma, immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve. 1
- Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals 1
- Total correction must never exceed 8 mmol/L in any 24-hour period to prevent osmotic demyelination syndrome 2, 1
- Monitor serum sodium every 2 hours during initial correction 2, 1
- Consider ICU admission for close monitoring 2
Moderate Symptomatic Hyponatremia
- Symptoms include nausea, vomiting, headache, weakness, gait instability 4
- Slower correction is appropriate: 4-8 mmol/L per day, not exceeding 8 mmol/L in 24 hours 2
- Monitor serum sodium every 4 hours after symptom resolution 1
Asymptomatic or Mild Hyponatremia
- Treatment focuses on addressing underlying cause and volume status 1
- Correction rate: 4-6 mmol/L per day for chronic cases 2
Treatment Based on Volume Status
Hypovolemic Hyponatremia
Discontinue diuretics immediately and administer isotonic (0.9%) saline for volume repletion. 1
- Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 2
- Urine sodium <30 mmol/L predicts good response to saline (71-100% positive predictive value) 2
- Continue until euvolemia achieved, then reassess 2
Euvolemic Hyponatremia (SIADH)
Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 2, 1
- If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 2
- For severe symptoms: 3% hypertonic saline with goal of 6 mmol/L correction over 6 hours 2
- Alternative pharmacological options for resistant cases:
Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)
Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L and treat the underlying condition. 1
- Discontinue diuretics temporarily if sodium <125 mmol/L 2
- For cirrhotic patients: consider albumin infusion (8 g per liter of ascites removed) alongside fluid restriction 2
- Avoid hypertonic saline unless life-threatening symptoms present, as it worsens ascites and edema 2
- Vasopressin receptor antagonists may be considered for persistent severe hyponatremia despite fluid restriction 1
Critical Correction Rate Guidelines
Standard-Risk Patients
- Maximum correction: 8 mmol/L in any 24-hour period 2, 1
- Target rate: 4-8 mmol/L per day, not exceeding 10-12 mmol/L in 24 hours 2
High-Risk Patients (Requires Slower Correction)
Patients with advanced liver disease, chronic alcoholism, malnutrition, or prior encephalopathy require correction of only 4-6 mmol/L per day, with an absolute maximum of 8 mmol/L in 24 hours. 2, 1
- These patients have 0.5-1.5% risk of osmotic demyelination syndrome even with careful correction 2
- Cirrhotic patients with sodium ≤130 mEq/L have increased risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 2
Management of Overcorrection
If sodium correction exceeds 8 mmol/L in 24 hours, immediately discontinue current fluids and switch to D5W (5% dextrose in water). 1
- Consider administering desmopressin to slow or reverse the rapid rise 2, 1
- Goal: bring total 24-hour correction back to ≤8 mmol/L from baseline 2
- Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 2
Special Considerations: Neurosurgical Patients
Distinguishing SIADH from Cerebral Salt Wasting (CSW)
- SIADH: euvolemic, treat with fluid restriction 2
- CSW: hypovolemic (CVP <6 cm H₂O), treat with volume and sodium replacement, never fluid restriction 2
- CSW requires isotonic or hypertonic saline, not fluid restriction 2
- For severe CSW: 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily 2
- In subarachnoid hemorrhage patients at risk of vasospasm: avoid fluid restriction and consider fludrocortisone or hydrocortisone 2
Common Pitfalls to Avoid
- Overly rapid correction exceeding 8 mmol/L in 24 hours causes osmotic demyelination syndrome 2
- Inadequate monitoring during active correction 2
- Using fluid restriction in CSW worsens outcomes 2
- Failing to recognize and treat the underlying cause 2
- Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 2
- Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—it increases fall risk (21% vs 5%) and mortality (60-fold increase with sodium <130 mmol/L) 2, 4
Monitoring Protocol
During Active Correction
- Severe symptoms: check sodium every 2 hours 2, 1
- Mild symptoms: check every 4 hours after symptom resolution 1
- Chronic hyponatremia: daily monitoring until target achieved 1