What is the approach to managing hyponatremia?

Approach to Hyponatremia

Initial Assessment and Classification

Begin by confirming true hypotonic hyponatremia through 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

The diagnostic workup should include:

• Serum and urine osmolality to confirm hypotonic hyponatremia and assess water excretion capacity 2
• Urine sodium concentration to differentiate between causes (>20-40 mmol/L suggests SIADH or renal losses; <30 mmol/L suggests extrarenal losses) 2, 3
• Serum creatinine, thyroid function (TSH), and cortisol to exclude endocrine causes 1
• Assessment of extracellular fluid volume status through physical examination, looking for orthostatic hypotension, dry mucous membranes (hypovolemia), or peripheral edema, ascites, jugular venous distention (hypervolemia) 2, 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. 2, 1

• Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 1, 4
• Never exceed 8 mmol/L total correction in 24 hours to prevent osmotic demyelination syndrome 2, 1, 3
• Monitor serum sodium every 2 hours during initial correction 2, 1

Asymptomatic or Mildly Symptomatic Hyponatremia

Treatment is based on volume status and underlying etiology, with slower correction rates 2, 1

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics immediately and administer isotonic (0.9%) saline for volume repletion. 2, 1

• Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 2
• Urine sodium <30 mmol/L predicts good response to saline (positive predictive value 71-100%) 2
• Once euvolemic, reassess and adjust treatment based on sodium response 2

Euvolemic Hyponatremia (SIADH)

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

• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 2
• For persistent cases, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily) with careful monitoring 2, 5
• Alternative 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. 2, 1

• Temporarily discontinue diuretics if sodium <125 mmol/L 2, 1
• For cirrhotic patients, consider albumin infusion alongside fluid restriction 2, 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens ascites and edema 2
• 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% placebo) 2, 5

Correction Rate Guidelines by Severity

The single most critical principle: never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome. 2, 1, 3

Standard Correction Rates

• Serum sodium 126-135 mmol/L: Continue current therapy with close electrolyte monitoring; no water restriction needed 1
• Serum sodium 121-125 mmol/L: More cautious approach; consider stopping diuretics 1
• Serum sodium <120 mmol/L: Stop diuretics immediately; implement severe fluid restriction plus albumin infusion or volume expansion 1

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

Patients with advanced liver disease, alcoholism, malnutrition, or prior encephalopathy require even more cautious correction due to dramatically higher risk of osmotic demyelination syndrome. 2, 1, 3

Additional high-risk factors include:

• Severe hyponatremia (<120 mmol/L) 2
• Hypophosphatemia, hypokalemia, hypoglycemia 2
• Low cholesterol 2

Special Considerations for Neurosurgical Patients

In neurosurgical patients, distinguishing between SIADH and cerebral salt wasting (CSW) is critical, as treatments are opposite. 2

SIADH Characteristics

• Euvolemic state with normal to slightly elevated central venous pressure 2
• Urine sodium >20-40 mmol/L with urine osmolality >300 mOsm/kg 2
• Treatment: Fluid restriction to 1 L/day 2

Cerebral Salt Wasting Characteristics

• True hypovolemia with CVP <6 cm H₂O 2
• Urine sodium >20 mmol/L despite volume depletion 2
• Clinical signs: orthostatic hypotension, dry mucous membranes 2
• Treatment: Volume and sodium replacement with isotonic or hypertonic saline, NEVER fluid restriction 2
• For severe symptoms, add fludrocortisone 0.1-0.2 mg daily 2
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 2

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, this is a medical emergency requiring immediate intervention. 2, 1

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

Monitoring During Treatment

Severe Symptoms

• Check serum sodium every 2 hours during initial correction 2, 1
• After symptom resolution, check every 4 hours 2

Mild Symptoms or Asymptomatic

• Check every 4 hours initially, then daily until target sodium achieved 1
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 2

Common Pitfalls to Avoid

• Never ignore mild hyponatremia (130-135 mmol/L) as it increases fall risk (21% vs. 5%) and mortality (60-fold increase with sodium <130 mmol/L) 2, 3
• Never use fluid restriction in cerebral salt wasting as this worsens outcomes 2
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms as it worsens fluid overload 2
• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours to avoid osmotic demyelination syndrome 2, 1, 3
• Never delay treatment while pursuing diagnosis in severely symptomatic patients 4
• Inadequate monitoring during active correction can lead to overcorrection 2