What is the approach to managing hyponatremia?

Hyponatremia Management

Initial Assessment and Classification

Hyponatremia (serum sodium <135 mEq/L) requires immediate assessment of symptom severity, volume status, and serum/urine osmolality to guide treatment. 1

• Confirm true hypotonic 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, 2
• Measure urine osmolality and urine sodium concentration to determine the underlying mechanism 1, 2
• Assess extracellular fluid volume status through physical examination: look for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemia) versus peripheral edema, ascites, jugular venous distention (hypervolemia) 1, 2
• Check serum creatinine, thyroid function, and cortisol to exclude endocrine causes 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, 4

• 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, 4

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends on volume status classification:

Treatment Based on Volume Status

Hypovolemic Hyponatremia (Urine Na <30 mmol/L)

Discontinue diuretics and administer isotonic (0.9%) saline for volume repletion. 1, 4

• Causes include gastrointestinal losses, diuretic use, burns, or third-spacing 5, 2
• Restore intravascular volume with normal saline until euvolemia is achieved 1, 4
• Avoid hypotonic fluids as they worsen hyponatremia 2

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1, 3, 4

• Diagnostic criteria: urine osmolality >100 mOsm/kg, urine sodium >20-40 mmol/L, normal thyroid/adrenal function, no diuretic use 1, 6
• If fluid restriction fails after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1
• For resistant cases, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1, 7, 3
• Alternative agents include urea, demeclocycline, or loop diuretics 1, 3, 5

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. 8, 1, 4

• Temporarily discontinue diuretics if sodium <125 mmol/L 8, 1
• In cirrhotic patients, consider albumin infusion (6-8 g per liter of ascites drained) alongside fluid restriction 8, 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens ascites and edema 8, 1
• Sodium restriction (not fluid restriction) is more effective for weight loss in cirrhosis, as fluid follows sodium 8, 1
• Tolvaptan may be considered for persistent hyponatremia despite fluid restriction, but use with extreme caution in cirrhosis due to increased gastrointestinal bleeding risk (10% vs 2% placebo) 1, 7

Correction Rate Guidelines by Severity

Serum Sodium 126-135 mmol/L

• Continue diuretic therapy with close electrolyte monitoring 8, 1
• No water restriction needed at this level 8, 1

Serum Sodium 121-125 mmol/L

• Stop diuretics or adopt a more cautious approach 8, 1
• Implement fluid restriction to 1-1.5 L/day if hypervolemic 8, 1
• If serum creatinine is elevated (>150 mmol/L or >120 mmol/L and rising), stop diuretics and provide volume expansion 8

Serum Sodium <120 mmol/L

• Stop diuretics immediately 8, 1
• For asymptomatic patients: severe fluid restriction plus albumin infusion (cirrhosis) or volume expansion with colloid/saline 8, 1
• Avoid increasing serum sodium by >8 mmol/L per 24 hours 8, 1, 3

Special Populations Requiring Slower Correction (4-6 mmol/L per day)

Patients with advanced liver disease, alcoholism, malnutrition, or prior encephalopathy require more cautious correction at 4-6 mmol/L per day due to higher risk of osmotic demyelination syndrome. 1, 3, 2

• Liver transplant recipients have a 0.5-1.5% risk of osmotic demyelination syndrome 1
• 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) 1

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 1
• Monitor for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Common Pitfalls to Avoid

• Never ignore mild hyponatremia (130-135 mmol/L)—it increases fall risk (21% vs 5%) and mortality (60-fold increase at <130 mmol/L) 1, 3
• Never use fluid restriction in cerebral salt wasting (neurosurgical patients)—this requires volume and sodium replacement 1
• Never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 3, 4
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 8, 1
• Never use lactated Ringer's solution for hyponatremia treatment—it is hypotonic (130 mEq/L sodium) and can worsen hyponatremia 1

Monitoring During Treatment

• Severe symptoms: Check serum sodium every 2 hours during initial correction 1
• Mild symptoms: Check every 4 hours after resolution of severe symptoms 1
• Once stable: Daily monitoring until target sodium achieved 1, 7
• Track daily weights in hypervolemic patients (aim for 0.5 kg/day loss without peripheral edema) 1