What are the steps for managing hyponatremia?

Hyponatremia Diagnosis and Management

Initial Diagnostic Workup

Begin by confirming true hyponatremia (serum sodium <135 mmol/L) and obtain serum osmolality, urine osmolality, urine sodium, and assess extracellular fluid volume status to determine the underlying cause. 1

• Check serum osmolality to exclude pseudohyponatremia (normal osmolality) or hyperglycemia-induced hyponatremia (high osmolality) 2
• Measure urine osmolality: <100 mOsm/kg suggests appropriate ADH suppression, while >100 mOsm/kg indicates impaired water excretion 1
• Obtain urine sodium concentration: <30 mmol/L suggests hypovolemia with 71-100% positive predictive value for saline responsiveness, while >20-40 mmol/L with high urine osmolality suggests SIADH 1
• Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 1

Volume Status Assessment

Physical examination alone has poor accuracy (sensitivity 41%, specificity 80%), so combine clinical findings with laboratory data 1:

• Hypovolemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
• Euvolemic signs: no edema, normal blood pressure, normal skin turgor, moist mucous membranes 1
• Hypervolemic signs: peripheral edema, ascites, jugular venous distention, pulmonary congestion 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Seizures, Coma, Altered Mental Status)

Administer 3% hypertonic saline immediately with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve, but never exceed 8 mmol/L total correction in 24 hours. 1, 3

• Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1
• Monitor serum sodium every 2 hours during initial correction 1
• Calculate sodium deficit: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1
• Critical safety limit: Maximum 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 3

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends on volume status:

Hypovolemic Hyponatremia

Discontinue diuretics and administer isotonic saline (0.9% NaCl) for volume repletion. 1

• Urine sodium <30 mmol/L predicts good response to saline with 71-100% positive predictive value 1
• Avoid hypotonic fluids as they worsen hyponatremia 1
• Once euvolemic, reassess and adjust therapy based on underlying cause 1

Euvolemic Hyponatremia (SIADH)

Implement fluid restriction to 1 L/day as first-line treatment. 1, 3

• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
• For persistent cases despite fluid restriction, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrating to 30-60 mg) 1, 4
• Alternative pharmacological options include urea, demeclocycline, or lithium (less commonly used due to side effects) 1, 3

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L. 1

• Temporarily discontinue diuretics if sodium <125 mmol/L 1
• In cirrhotic patients, consider albumin infusion alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens ascites and edema 1
• Tolvaptan may be considered for persistent severe hyponatremia despite fluid restriction, but use with extreme caution in cirrhosis due to 10% risk of gastrointestinal bleeding (vs. 2% with placebo) 4

Special Populations and High-Risk Considerations

Patients at High Risk for Osmotic Demyelination Syndrome

Use more conservative correction rates of 4-6 mmol/L per day (maximum 8 mmol/L in 24 hours) in patients with advanced liver disease, alcoholism, malnutrition, or prior encephalopathy. 1

• Risk of osmotic demyelination syndrome is 0.5-1.5% in liver transplant recipients 1
• If overcorrection occurs, immediately discontinue current fluids, switch to D5W, and consider desmopressin to slow or reverse the rapid rise 1

Neurosurgical Patients: SIADH vs. Cerebral Salt Wasting (CSW)

Distinguish between SIADH and CSW as treatment approaches are fundamentally opposite. 1

SIADH characteristics:

• Euvolemic state with normal to slightly elevated central venous pressure 1
• Urine sodium >20-40 mmol/L with urine osmolality >300 mOsm/kg 1
• Treatment: Fluid restriction to 1 L/day 1

CSW characteristics:

• True hypovolemia with CVP <6 cm H₂O, hypotension, tachycardia 1
• Urine sodium >20 mmol/L despite volume depletion 1
• Treatment: Volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1
• For severe symptoms, use 3% hypertonic saline plus fludrocortisone 0.1-0.2 mg daily 1
• In subarachnoid hemorrhage patients at risk for vasospasm, avoid fluid restriction and consider hydrocortisone to prevent natriuresis 1

Cirrhotic Patients

Hyponatremia in cirrhosis significantly increases risk of complications: spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36). 1

• Hyponatremia is mostly dilutional and defined at serum sodium <130 mmol/L 1
• Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1
• Albumin infusion may improve serum sodium levels 1
• Tolvaptan carries higher risk of gastrointestinal bleeding (10% vs. 2% placebo) and increased all-cause mortality with long-term use 4

Critical Safety Considerations and Common Pitfalls

Osmotic Demyelination Syndrome Prevention

Never exceed 8 mmol/L correction in 24 hours; symptoms typically occur 2-7 days after rapid correction and include dysarthria, dysphagia, oculomotor dysfunction, and quadriparesis. 1

• For average-risk patients: aim for 4-8 mmol/L per day, not exceeding 10-12 mmol/L in 24 hours 1
• For high-risk patients: aim for 4-6 mmol/L per day, not exceeding 8 mmol/L in 24 hours 1

Common Pitfalls to Avoid

• Ignoring mild hyponatremia (130-135 mmol/L): Even mild hyponatremia increases fall risk (21% vs. 5% in normonatremic patients) and mortality (60-fold increase with sodium <130 mmol/L) 1, 3
• Using fluid restriction in CSW: This worsens outcomes; CSW requires volume and sodium replacement 1
• Inadequate monitoring during active correction: Check sodium every 2 hours for severe symptoms, every 4 hours after symptom resolution 1
• Failing to recognize and treat the underlying cause: Always identify and address the primary etiology 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms: This worsens fluid overload 1

Monitoring During Treatment

• Severe symptoms: Monitor serum sodium every 2 hours during initial correction 1
• Mild symptoms: Monitor every 4 hours after resolution of severe symptoms 1
• Chronic management: Daily monitoring initially, then adjust frequency based on response 1
• Track daily weights, fluid balance, and watch for signs of overcorrection or osmotic demyelination syndrome 1