What is the approach to managing hyponatremia?

Comprehensive Approach to Hyponatremia

Initial Assessment and Classification

Hyponatremia should be further investigated and treated when serum sodium is less than 131 mmol/L, though even mild hyponatremia (130-135 mmol/L) requires attention as it increases fall risk (21% vs 5%) and mortality. 1, 2

Essential Initial Workup

• Measure serum and urine osmolality, urine sodium, and uric acid 2
• Assess extracellular fluid volume status through physical examination: look for orthostatic hypotension, dry mucous membranes, skin turgor, jugular venous distention, peripheral edema, and ascites 1, 2
• Check serum creatinine, blood urea nitrogen, glucose, thyroid-stimulating hormone, and cortisol to rule out secondary causes 2
• Obtaining antidiuretic hormone and natriuretic peptide levels is not supported by evidence 1

Volume Status Classification

• Hypovolemic: orthostatic hypotension, dry mucous membranes, decreased skin turgor, urine sodium typically <30 mmol/L 2
• Euvolemic: no edema, normal blood pressure, normal skin turgor, moist mucous membranes 2
• Hypervolemic: peripheral edema, ascites, jugular venous distention, pulmonary congestion 2

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. 2, 3

• Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals 2
• Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 2
• Monitor serum sodium every 2 hours during initial correction 2
• ICU admission is recommended for close monitoring 2

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment depends on volume status and underlying etiology 2

Treatment Based on Volume Status and Etiology

Hypovolemic Hyponatremia

Discontinue diuretics and administer isotonic (0.9%) saline for volume repletion. 2

• Urine sodium <30 mmol/L has 71-100% positive predictive value for response to saline 2
• Once euvolemic, reassess and adjust treatment based on sodium response 2
• Avoid hypotonic fluids as they 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 2
• For resistant cases, consider:
  • Urea (40 g in 100-150 mL normal saline every 8 hours) 1, 2
  • Demeclocycline 1
  • Lithium 1
  • Loop diuretics 1
• Tolvaptan 15 mg once daily, titrated to 30-60 mg, may be used for clinically significant hyponatremia resistant to fluid restriction 2, 4
• Monitor for overly rapid correction with vaptans 2, 4

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

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

• Discontinue diuretics temporarily if sodium <125 mmol/L 2
• In cirrhotic patients, consider albumin infusion (6-8 g per liter of ascites drained) 2
• Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens edema and ascites 2
• Sodium restriction (2-2.5 g/day) is more effective than fluid restriction for weight loss, as fluid follows sodium 2
• Vaptans may be considered but carry higher risk of gastrointestinal bleeding in cirrhosis (10% vs 2%) 2, 4

Special Considerations for Neurosurgical Patients

Distinguishing SIADH from Cerebral Salt Wasting (CSW)

In neurosurgical patients, CSW is more common than SIADH and requires fundamentally different treatment. 1, 2

Cerebral Salt Wasting

• Evidence of volume depletion: hypotension, tachycardia, dry mucous membranes 2
• Urine sodium typically >20 mmol/L with high urine osmolality 2
• Treatment: volume and sodium replacement with isotonic or hypertonic saline, NOT fluid restriction 1, 2
• For severe symptoms: 3% hypertonic saline plus fludrocortisone 1, 2
• Hydrocortisone may prevent natriuresis in subarachnoid hemorrhage patients 1

Subarachnoid Hemorrhage Patients

• Hyponatremia should NOT be treated with fluid restriction in patients at risk of vasospasm 1
• Fludrocortisone may be considered to prevent vasospasm 1
• Aggressive volume resuscitation is appropriate 2

Correction Rate Guidelines and Osmotic Demyelination Prevention

The serum sodium level should not be corrected by more than 8 mmol/L in 24 hours. 1, 2

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

• Advanced liver disease 2
• Alcoholism 2
• Malnutrition 2
• Prior encephalopathy 2
• Severe hyponatremia (<120 mmol/L) 2

Managing Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, immediately discontinue current fluids and switch to D5W (5% dextrose in water). 2

• Consider administering desmopressin to slow or reverse the rapid rise 2
• Watch for signs of osmotic demyelination syndrome 2-7 days after rapid correction: dysarthria, dysphagia, oculomotor dysfunction, quadriparesis 2

Common Pitfalls to Avoid

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

Monitoring During Treatment

• Severe symptoms: check sodium every 2 hours during initial correction 2
• After symptom resolution: check sodium every 4 hours, then daily 2
• Monitor for signs of volume overload or depletion 2
• Assess for neurological changes suggesting osmotic demyelination 2