What is the initial approach to treating hyponatraemia?

Initial Approach to Treating Hyponatraemia

The initial approach to treating hyponatraemia depends critically on symptom severity and volume status: severely symptomatic patients require immediate 3% hypertonic saline to correct sodium by 6 mmol/L over 6 hours, while asymptomatic patients should be managed based on their volume status with fluid restriction for euvolaemic/hypervolaemic states or isotonic saline for hypovolaemic states. 1

Immediate Assessment

Determine symptom severity first - this dictates urgency of treatment 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, guided by volume status 1
• Asymptomatic = treat underlying cause, avoid rapid correction 1, 3

Assess volume status through physical examination 1:

• Hypovolaemic signs: orthostatic hypotension, dry mucous membranes, decreased skin turgor, flat neck veins 1
• Euvolaemic: no edema, normal blood pressure, normal skin turgor 1
• Hypervolaemic signs: peripheral edema, ascites, jugular venous distention, pulmonary congestion 1

Treatment Algorithm Based on Symptom Severity

For Severe Symptomatic Hyponatraemia (Medical Emergency)

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

• Give as 100-150 mL IV bolus over 10 minutes, can repeat up to 3 times at 10-minute intervals 1
• Target: increase sodium by 6 mmol/L over first 6 hours OR until symptoms resolve 1
• Critical safety limit: never exceed 8 mmol/L correction in 24 hours to prevent osmotic demyelination syndrome 1, 2
• Monitor serum sodium every 2 hours during initial correction 1

For Asymptomatic or Mildly Symptomatic Hyponatraemia

Treatment is determined by volume status 1:

Hypovolaemic hyponatraemia 1:

• Discontinue diuretics immediately 1
• Administer isotonic saline (0.9% NaCl) for volume repletion 1
• Urine sodium <30 mmol/L predicts good response to saline (positive predictive value 71-100%) 1

Euvolaemic hyponatraemia (SIADH) 1, 3:

• First-line: Fluid restriction to 1 L/day 1
• If no response after 24-48 hours, add oral sodium chloride 100 mEq three times daily 1
• Second-line options if resistant: urea or tolvaptan 3
• Note: Almost half of SIADH patients do not respond to fluid restriction alone 3

Hypervolaemic hyponatraemia (heart failure, cirrhosis) 1:

• 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 - it worsens edema and ascites 1

Specific Sodium Level Thresholds

Sodium 126-135 mmol/L 4:

• Continue diuretic therapy with close electrolyte monitoring 4
• Do NOT water restrict 4

Sodium 121-125 mmol/L 4:

• International opinion: continue diuretics 4
• More cautious approach: stop or reduce diuretics 4
• If creatinine elevated: stop diuretics and give volume expansion 4

Sodium ≤120 mmol/L 4:

• Stop diuretics immediately 4
• Most patients should undergo volume expansion with colloid (haemaccel, gelofusine, voluven) or saline 4
• Critical: avoid increasing sodium by >12 mmol/L per 24 hours 4

Essential Initial Workup

Obtain these tests immediately 1:

• Serum osmolality (to exclude pseudohyponatraemia) 1
• Urine osmolality and urine sodium concentration 1
• Serum creatinine and electrolytes 1
• Thyroid-stimulating hormone (to exclude hypothyroidism) 1
• Serum uric acid (<4 mg/dL suggests SIADH with 73-100% positive predictive value) 1

Critical Correction Rate Guidelines

Standard patients: 4-8 mmol/L per day, maximum 8 mmol/L in 24 hours 1

High-risk patients (advanced liver disease, alcoholism, malnutrition, prior encephalopathy): 4-6 mmol/L per day, maximum 8 mmol/L in 24 hours 1, 2

Exceeding these limits risks osmotic demyelination syndrome - a devastating neurological complication causing dysarthria, dysphagia, quadriparesis, or death 1, 2

Common Pitfalls to Avoid

• Never use fluid restriction in hypovolaemic hyponatraemia - this worsens the condition 1
• Never use hypertonic saline in hypervolaemic hyponatraemia without severe symptoms - worsens fluid overload 1
• Never correct chronic hyponatraemia faster than 8 mmol/L in 24 hours - risks osmotic demyelination 1, 2
• Never ignore mild hyponatraemia (130-135 mmol/L) - associated with increased falls, fractures, and mortality 1, 2
• In neurosurgical patients, distinguish SIADH from cerebral salt wasting - they require opposite treatments (fluid restriction vs. volume replacement) 1

Special Consideration: Cirrhotic Patients

Hyponatraemia in cirrhosis requires particularly cautious management 4, 1:

• Water restriction has controversial benefit and may worsen effective hypovolaemia 4
• Some experts advocate plasma expansion rather than water restriction 4
• Hyponatraemia increases risk of hepatorenal syndrome, spontaneous bacterial peritonitis, and hepatic encephalopathy 1
• Avoid rapid correction - these patients are at highest risk for osmotic demyelination 1