What is the management of hyponatremia?

Management of Hyponatremia

Initial Assessment and Classification

Hyponatremia (serum sodium <135 mmol/L) requires systematic evaluation based on volume status, symptom severity, and chronicity to guide appropriate treatment and avoid life-threatening complications. 1

• Investigate and treat when serum sodium falls below 131 mmol/L, though even mild hyponatremia (130-135 mmol/L) warrants attention due to increased fall risk and mortality 1, 2
• Obtain initial workup including serum and urine osmolality, urine electrolytes (particularly urine sodium), uric acid, and assessment of extracellular fluid volume status 1, 2
• Classify patients by volume status: hypovolemic (orthostatic hypotension, dry mucous membranes, decreased skin turgor), euvolemic (no edema, normal blood pressure), or hypervolemic (peripheral edema, ascites, jugular venous distention) 1, 3
• Determine chronicity: acute (<48 hours) versus chronic (>48 hours), as this fundamentally changes correction rate limits 1, 4

Common pitfall: Physical examination alone has poor accuracy for volume assessment (sensitivity 41.1%, specificity 80%), so supplement with laboratory findings 1

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

For patients with severe symptoms (seizures, coma, altered mental status, cardiorespiratory distress), immediately administer 3% hypertonic saline with a target correction of 6 mmol/L over 6 hours or until symptoms resolve. 1, 3

• Administer 3% hypertonic saline as 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1, 4
• Critical safety limit: Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2, 3
• Monitor serum sodium every 2 hours during initial correction phase 1, 2
• Consider ICU admission for close monitoring during active treatment 1

High-risk populations requiring even slower correction (4-6 mmol/L per day): patients with advanced liver disease, alcoholism, malnutrition, severe hyponatremia, or prior encephalopathy 1, 2

Mild to Moderate Symptomatic or Asymptomatic Hyponatremia

Treatment depends on volume status and underlying etiology rather than immediate hypertonic saline 1, 5

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Restore intravascular volume with isotonic (0.9%) saline, as volume depletion is the primary problem. 1, 2

• Urine sodium <30 mmol/L predicts good response to saline infusion (positive predictive value 71-100%) 1, 2
• Discontinue diuretics that may be contributing 1, 2
• Once euvolemic, reassess sodium levels and adjust management accordingly 1

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment for SIADH. 1, 2, 3

• If no response to fluid restriction after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1, 2
• For resistant cases, consider pharmacological options: urea, demeclocycline, lithium, or loop diuretics 1, 2
• Vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) may be considered for persistent hyponatremia despite fluid restriction 1, 6, 3
• Monitor serum sodium every 24 hours initially when using vaptans to avoid overly rapid correction 6

Important distinction in neurosurgical patients: Cerebral salt wasting (CSW) mimics SIADH but requires opposite treatment—volume and sodium replacement, NOT fluid restriction 1, 2

• CSW characteristics: true hypovolemia (CVP <6 cm H₂O), high urine sodium >20 mmol/L despite volume depletion, evidence of extracellular volume depletion 1
• CSW treatment: isotonic or hypertonic saline plus fludrocortisone 0.1-0.2 mg daily for severe cases 1, 2
• Critical error: Using fluid restriction in CSW worsens outcomes and can be fatal 1, 2

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L. 1, 2, 5

• Temporarily discontinue diuretics if sodium <125 mmol/L 1, 2
• In cirrhotic patients, consider albumin infusion (6-8 g per liter of ascites drained) alongside fluid restriction 1, 2
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens ascites and edema 1, 2
• Vasopressin receptor antagonists may be considered for persistent severe hyponatremia despite fluid restriction and maximization of guideline-directed medical therapy 1, 6

Special consideration for cirrhosis: Tolvaptan carries higher risk of gastrointestinal bleeding (10% vs 2% placebo) and should be used with extreme caution 1, 6

Correction Rate Guidelines and Prevention of Osmotic Demyelination Syndrome

The maximum correction rate is 8 mmol/L in 24 hours for average-risk patients; 4-6 mmol/L per day for high-risk patients. 1, 2, 3

• Calculate sodium deficit: Desired increase in Na (mEq/L) × (0.5 × ideal body weight in kg) 1, 2
• Monitor sodium levels: every 2 hours for severe symptoms, every 4 hours after symptom resolution 1, 2
• Watch for osmotic demyelination syndrome signs (typically 2-7 days post-correction): dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 1, 2

If overcorrection occurs (>8 mmol/L in 24 hours):

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1, 2
• Consider administering desmopressin to slow or reverse the rapid rise 1, 2
• Goal: bring total 24-hour correction to no more than 8 mmol/L from starting point 1

Special Populations and Clinical Scenarios

Neurosurgical Patients (Subarachnoid Hemorrhage, Brain Injury)

• Cerebral salt wasting is more common than SIADH in this population 1, 2
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1, 2
• Consider fludrocortisone to prevent vasospasm and hydrocortisone to prevent natriuresis 1, 2

Cirrhotic Patients

• Hyponatremia (sodium <130 mmol/L) increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1, 2
• Require more cautious correction rates (4-6 mmol/L per day) due to higher osmotic demyelination risk 1, 2
• Sodium restriction (not fluid restriction) results in weight loss, as fluid passively follows sodium 1, 2

Patients on Diuretics

• For sodium 126-135 mmol/L with normal creatinine: continue diuretics with close electrolyte monitoring 1, 2
• For sodium <125 mmol/L: temporarily discontinue diuretics until sodium improves 1, 2

Common Pitfalls to Avoid

• Overly rapid correction (>8 mmol/L in 24 hours) causing osmotic demyelination syndrome 1, 2, 3
• Using fluid restriction in cerebral salt wasting, which worsens outcomes 1, 2
• Inadequate monitoring during active correction 1, 2
• Failing to recognize and treat the underlying cause 1, 2
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1, 2
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—it increases fall risk (21% vs 5%) and mortality (60-fold increase at <130 mmol/L) 1, 3
• Misdiagnosing volume status in heart failure patients, leading to inappropriate normal saline administration 1, 2