What is the initial approach to managing hyponatremia?

Initial Approach to Managing Hyponatremia

Begin by assessing volume status, symptom severity, and serum/urine osmolality to determine the underlying cause and guide treatment—this initial evaluation dictates whether you use hypertonic saline for emergencies, fluid restriction for SIADH, or isotonic saline for volume depletion. 1

Immediate Assessment Steps

Determine symptom severity first, as this drives urgency of intervention 1:

• Severe symptoms (seizures, coma, altered mental status, cardiorespiratory distress): Medical emergency requiring immediate hypertonic saline 1, 2
• Mild symptoms (nausea, headache, confusion): Less urgent, allows time for diagnostic workup 1
• Asymptomatic: Proceed with systematic evaluation 1

Obtain essential laboratory tests 1:

• Serum osmolality (to exclude pseudohyponatremia from hyperglycemia or hyperlipidemia) 3, 4
• Urine osmolality and urine sodium concentration 1, 3
• Serum uric acid (<4 mg/dL suggests SIADH with 73-100% positive predictive value) 1
• Assessment of extracellular fluid volume status 1

Volume Status Classification

Assess volume status through physical examination 1:

Hypovolemic signs (true volume depletion) 1, 3:

• Orthostatic hypotension, tachycardia
• Dry mucous membranes, decreased skin turgor
• Flat neck veins

Euvolemic signs (normal volume status) 1:

• No edema, no orthostatic hypotension
• Normal skin turgor, moist mucous membranes

Hypervolemic signs (volume overload) 1, 3:

• Peripheral edema, ascites
• Jugular venous distention
• Pulmonary congestion

Treatment Algorithm Based on Severity and Volume Status

For Severe Symptomatic Hyponatremia (Emergency)

Administer 3% hypertonic saline immediately 1, 2, 5:

• Give 100-150 mL bolus over 10 minutes, can repeat up to 3 times 1
• Target: Increase sodium by 6 mmol/L over first 6 hours or until symptoms resolve 1
• Critical safety limit: Do not exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 6, 2
• Monitor serum sodium every 2 hours during initial correction 1

For Hypovolemic Hyponatremia

Discontinue diuretics and administer isotonic saline (0.9% NaCl) for volume repletion 1:

• Urine sodium <30 mmol/L predicts good response to saline (71-100% positive predictive value) 1
• Continue until euvolemia achieved 1
• Still respect the 8 mmol/L/24-hour correction limit 1

For Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment 1, 2, 7:

• For mild/asymptomatic cases: Start with 1000 mL/day fluid restriction 1
• If no response to fluid restriction: Add oral sodium chloride 100 mEq three times daily 1
• For severe symptoms: Use 3% hypertonic saline with careful monitoring 1

For Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 1:

• Discontinue diuretics temporarily if sodium <125 mmol/L 1
• Consider albumin infusion in cirrhotic patients 1
• Avoid hypertonic saline unless life-threatening symptoms present, as it worsens edema and ascites 1

Critical Correction Rate Guidelines

Maximum correction rates to prevent osmotic demyelination syndrome 1, 6, 2:

• Standard patients: 8 mmol/L per 24 hours maximum 1
• High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): 4-6 mmol/L per day maximum 1
• For severe symptoms: Correct 6 mmol/L over 6 hours, then slow down 1

Special Considerations for Neurosurgical Patients

Distinguish between SIADH and Cerebral Salt Wasting (CSW), as treatments are opposite 1:

CSW characteristics 1:

• True hypovolemia with low central venous pressure
• High urine sodium >20 mmol/L despite volume depletion
• Treatment: Volume and sodium replacement, NOT fluid restriction 1
• Consider fludrocortisone for severe symptoms 1

SIADH characteristics 1:

• Euvolemia
• Urine sodium >20-40 mmol/L with urine osmolality >300 mOsm/kg
• Treatment: Fluid restriction 1

Common Pitfalls to Avoid

• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours—this causes osmotic demyelination syndrome 1, 2
• Never use fluid restriction in Cerebral Salt Wasting—this worsens outcomes 1
• Never ignore mild hyponatremia (130-135 mmol/L)—it increases fall risk (21% vs 5%) and mortality (60-fold increase) 1
• Never use hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms—it worsens fluid overload 1
• Inadequate monitoring during active correction leads to overcorrection 1

Monitoring Requirements

During active correction 1:

• Severe symptoms: Check sodium every 2 hours 1
• Mild symptoms: Check sodium every 4 hours 1
• Watch for osmotic demyelination syndrome signs (dysarthria, dysphagia, quadriparesis) typically 2-7 days after rapid correction 1