How should hyponatraemia be treated based on severity, symptomatology, chronicity, and volume status?

Treatment of Hyponatremia

Hyponatremia treatment must be guided by symptom severity, chronicity, and volume status, with the overriding principle that correction should never exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome. 1

Immediate Assessment

Determine symptom severity first—this dictates urgency:

• Severe symptoms (seizures, coma, altered consciousness, respiratory distress) constitute a medical emergency requiring immediate hypertonic saline regardless of sodium level 1, 2, 3
• Mild-moderate symptoms include nausea, vomiting, headache, confusion, weakness, and gait instability 2, 3
• Asymptomatic patients can be managed more conservatively with slower correction 1, 3

Assess chronicity:

• Acute hyponatremia (<48 hours) causes more severe symptoms at the same sodium level and can be corrected more rapidly 2, 4
• Chronic hyponatremia (>48 hours) requires slower correction due to brain adaptation and higher risk of osmotic demyelination 1, 4

Determine volume status through physical examination (orthostatic hypotension, skin turgor, edema, ascites, jugular venous distension) to classify as hypovolemic, euvolemic, or hypervolemic 1, 3, 5

Treatment Based on Symptom Severity

Severe Symptomatic Hyponatremia (Medical Emergency)

Administer 3% hypertonic saline immediately with a target correction of 6 mmol/L over 6 hours or until severe symptoms resolve 1, 3, 6

• Give 100 mL boluses of 3% saline over 10 minutes, repeatable up to three times at 10-minute intervals until symptoms improve 3, 7
• Monitor serum sodium every 2 hours during initial correction 1, 3
• Total correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 1, 3, 6
• Once severe symptoms resolve, switch to slower correction strategy based on volume status 1, 3

Mild-Moderate Symptomatic or Asymptomatic Hyponatremia

Treatment depends on volume status and underlying cause 1, 3, 5

Treatment Based on Volume Status

Hypovolemic Hyponatremia

Discontinue diuretics immediately and administer isotonic (0.9%) saline for volume repletion 1, 3, 5

• Initial infusion rate: 15-20 mL/kg/h, then 4-14 mL/kg/h based on response 1
• Urine sodium <30 mmol/L predicts good response to saline (positive predictive value 71-100%) 1
• Continue until euvolemia achieved, then reassess sodium level 1
• Common causes: diuretics, gastrointestinal losses, third-spacing 1, 5

Euvolemic Hyponatremia (SIADH)

Fluid restriction to 1 L/day is the cornerstone of treatment 1, 3, 6

• If no response to fluid restriction, add oral sodium chloride 100 mEq three times daily 1
• For resistant cases, consider vasopressin receptor antagonists (tolvaptan 15 mg once daily, titrate to 30-60 mg) 1, 6
• Alternative options: urea, demeclocycline, lithium, loop diuretics 1, 6
• Monitor serum sodium every 24 hours initially to ensure safe correction 1, 3

Hypervolemic Hyponatremia (Heart Failure, Cirrhosis)

Implement fluid restriction to 1-1.5 L/day for serum sodium <125 mmol/L 1, 3, 5

• Treat the underlying condition (optimize heart failure therapy, manage cirrhosis) 1, 3, 5
• Discontinue or reduce diuretics temporarily if sodium <125 mmol/L 1, 3
• For cirrhotic patients, consider albumin infusion (8 g per liter of ascites removed) alongside fluid restriction 1
• Avoid hypertonic saline unless life-threatening symptoms are present, as it worsens edema and ascites 1
• Vasopressin receptor antagonists may be considered for persistent severe hyponatremia despite fluid restriction 1, 6

Correction Rate Guidelines by Severity

Standard Correction Rates

• Maximum correction: 8 mmol/L in 24 hours for all patients 1, 3, 6
• Target correction: 4-8 mmol/L per day, not exceeding 10-12 mmol/L in 24 hours 1
• For severe symptomatic hyponatremia: 6 mmol/L over first 6 hours, then slow to stay within 8 mmol/L/24h limit 1, 3

High-Risk Patients Requiring Slower Correction (4-6 mmol/L per day, maximum 8 mmol/L in 24 hours)

Patients with advanced liver disease, chronic alcoholism, malnutrition, or prior encephalopathy have exceptionally high risk of osmotic demyelination syndrome 1, 3

• These patients have a 0.5-1.5% risk of osmotic demyelination even with careful correction 1
• Never exceed 8 mmol/L in 24 hours in these populations 1, 3

Management by Sodium Level

• Sodium 126-135 mmol/L: Continue current therapy with close monitoring; no water restriction needed at this level 1, 3
• Sodium 121-125 mmol/L: Implement fluid restriction (hypervolemic/euvolemic) or volume expansion (hypovolemic); consider discontinuing diuretics 1, 3
• Sodium ≤120 mmol/L: Stop diuretics immediately; severe fluid restriction plus albumin (hypervolemic) or aggressive volume expansion (hypovolemic) 1, 3

Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours, this is a medical emergency requiring immediate intervention 1, 3

• Immediately discontinue current fluids and switch to D5W (5% dextrose in water) 1
• Consider administering desmopressin to slow or reverse the rapid rise 1
• Goal: bring total 24-hour correction back to ≤8 mmol/L from baseline 1
• Watch for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) typically occurring 2-7 days after rapid correction 1

Monitoring During Treatment

Severe Symptoms

• Check serum sodium every 2 hours during initial correction 1, 3
• Continue every 4 hours after resolution of severe symptoms 1, 3

Mild Symptoms or Asymptomatic

• Check every 4-6 hours while actively correcting 1, 3
• Daily monitoring until target sodium achieved 3

Special Populations

Cirrhotic Patients

• Sodium ≤130 mEq/L increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 1, 3
• Correction rate must be 4-6 mmol/L per day (maximum 8 mmol/L in 24 hours) 1
• Albumin infusion alongside fluid restriction is beneficial 1
• Hypertonic saline should be avoided unless life-threatening symptoms 1

Neurosurgical Patients

Distinguish between SIADH and cerebral salt wasting (CSW)—they require opposite treatments 1

• SIADH: euvolemic, treat with fluid restriction 1
• CSW: hypovolemic, treat with volume and sodium replacement (isotonic or hypertonic saline), never fluid restriction 1
• In subarachnoid hemorrhage at risk for vasospasm, fluid restriction is contraindicated 1
• Consider fludrocortisone 0.1-0.2 mg daily for severe CSW 1

Critical Pitfalls to Avoid

• Overly rapid correction (>8 mmol/L in 24 hours) causes osmotic demyelination syndrome 1, 3, 6
• Inadequate monitoring during active correction 1
• Using fluid restriction in cerebral salt wasting worsens outcomes 1
• Failing to recognize and treat the underlying cause 1
• Using hypertonic saline in hypervolemic hyponatremia without life-threatening symptoms 1
• Ignoring mild hyponatremia (130-135 mmol/L) as clinically insignificant—it increases mortality 60-fold and fall risk 1, 2, 3
• Delaying treatment while pursuing diagnostic workup in severely symptomatic patients 3, 7