What is the approach to managing hyponatremia?

Hyponatremia Management

Initial Assessment and Classification

Confirm true hypotonic hyponatremia by checking serum osmolality (<275 mOsm/kg) and exclude pseudohyponatremia from hyperglycemia by correcting sodium (add 1.6 mEq/L for each 100 mg/dL glucose >100 mg/dL). 1

• Assess extracellular fluid volume status through physical examination, looking specifically for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemia), or jugular venous distention, peripheral edema, ascites, and pulmonary congestion (hypervolemia) 1, 2
• Check serum creatinine, thyroid function (TSH), and cortisol to exclude endocrine causes 1
• Measure urine sodium and osmolality: urine sodium <30 mmol/L suggests hypovolemia with 71-100% positive predictive value for response to saline, while >20 mEq/L with high urine osmolality (>500 mOsm/kg) suggests SIADH 1, 2

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (seizures, coma, altered mental status)

Administer 3% hypertonic saline immediately as 100 mL boluses over 10 minutes, repeatable up to three times at 10-minute intervals, with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve. 1, 2

• Never exceed 8 mmol/L total correction in 24 hours to prevent osmotic demyelination syndrome 1, 2
• Monitor serum sodium every 2 hours during initial correction 1
• Consider ICU admission for close monitoring during treatment 2

Mild to Moderate Symptomatic or Asymptomatic Hyponatremia

Treatment depends on volume status and underlying etiology 1, 2

Treatment Based on Volume Status

Hypovolemic Hyponatremia

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

• Once euvolemic, reassess and adjust management based on sodium response 1
• Avoid hypotonic fluids as they will worsen hyponatremia 2

Euvolemic Hyponatremia (SIADH)

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

• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1, 2
• For persistent cases despite fluid restriction, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrating to 30-60 mg as needed) 1, 3
• Alternative pharmacological options include urea, demeclocycline, or lithium for resistant cases 2

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, 2

• Discontinue diuretics temporarily if sodium <125 mmol/L 1, 2
• Consider albumin infusion in cirrhotic patients alongside fluid restriction 1, 2
• Avoid hypertonic saline unless life-threatening symptoms are present, as it may worsen edema and ascites 1, 2
• Vasopressin receptor antagonists may be considered for persistent severe hyponatremia despite fluid restriction and maximization of guideline-directed medical therapy, but use with extreme caution in cirrhosis due to 10% risk of gastrointestinal bleeding versus 2% with placebo 1, 3

Correction Rate Guidelines by Severity

Standard Correction Rates

• For serum sodium 126-135 mmol/L: Continue diuretic therapy with close electrolyte monitoring; water restriction is not recommended at this level 1
• For serum sodium 121-125 mmol/L: More cautious approach warranted; consider stopping diuretics 1
• For serum sodium <120 mmol/L: Stop diuretics immediately and consider severe fluid restriction plus albumin infusion or volume expansion 1

Maximum Correction Limits

The absolute maximum correction is 8 mmol/L per 24 hours for all patients to prevent osmotic demyelination syndrome. 1, 2, 4

Special Populations Requiring Slower Correction

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, 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) 1, 2
• Even mild hyponatremia (130-135 mmol/L) increases fall risk (21% vs 5% in normonatremic patients) and mortality (60-fold increase with sodium <130 mmol/L) 1, 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), and consider administering desmopressin to slow or reverse the rapid rise. 1, 2

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

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
• Continue daily monitoring until target sodium achieved 1

Special Considerations for Neurosurgical Patients

In neurosurgical patients, distinguish between SIADH and cerebral salt wasting (CSW), as treatment approaches differ fundamentally. 1, 2

• CSW requires volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1, 2
• For severe CSW symptoms, administer 3% hypertonic saline plus fludrocortisone in ICU 2
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 1, 2
• Consider fludrocortisone or hydrocortisone to prevent natriuresis in subarachnoid hemorrhage patients 1, 2

Common Pitfalls to Avoid

• Overly rapid correction exceeding 8 mmol/L in 24 hours leading to osmotic demyelination syndrome 1, 2
• Using fluid restriction in cerebral salt wasting, which worsens outcomes 1, 2
• Failing to recognize and treat the underlying cause 1, 2
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1, 2
• Inadequate monitoring during active correction 1, 2
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant 1, 2