How to manage hyponatremia in patients undergoing dialysis?

Management of Hyponatremia in Dialysis Patients

Critical Safety Principle

In dialysis patients with severe hyponatremia, the primary goal is preventing osmotic demyelination syndrome by limiting sodium correction to ≤8 mmol/L per 24 hours, regardless of the dialysis modality used. 1

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Initial Assessment

Before initiating dialysis in hyponatremic patients, determine:

• Severity of hyponatremia: Mild (130-135 mmol/L), moderate (120-129 mmol/L), or severe (<120 mmol/L) 1
• Symptom severity: Severe symptoms (seizures, altered mental status, coma) require immediate intervention; asymptomatic or mild symptoms allow for controlled correction 1
• Chronicity: Chronic hyponatremia (>48 hours) requires slower correction than acute (<48 hours) 1
• Volume status: Hypovolemic, euvolemic, or hypervolemic—this guides fluid management alongside dialysis 1
• High-risk features: Advanced liver disease, alcoholism, malnutrition, or prior encephalopathy require even more cautious correction (4-6 mmol/L per day maximum) 1

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Dialysis Prescription Modifications for Severe Hyponatremia

For Conventional Hemodialysis

The key strategy is using low dialysate sodium concentration combined with reduced blood flow rates to control the rate of sodium correction. 2, 3

• Dialysate sodium: Set to 128-130 mEq/L (the lowest permissible level on most conventional HD machines) 2, 3
• Blood flow rate: Start at 50 mL/min for the first session, which typically achieves sodium correction of approximately 1-2 mEq/L per hour 2, 3
• Subsequent sessions: If tolerated, blood flow can be increased to 100 mL/min, achieving approximately 2 mEq/L per hour correction 2
• Monitoring: Check serum sodium every 2 hours during the initial dialysis session, then adjust the prescription to ensure total correction does not exceed 8 mmol/L in 24 hours 1, 2

This approach successfully corrects uremia and volume overload while preventing overly rapid sodium correction, even in resource-limited settings without CRRT availability 2, 3

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For Continuous Renal Replacement Therapy (CRRT)

CRRT is the ideal modality for managing severe hyponatremia in dialysis-dependent patients, but requires specific modifications to prevent overcorrection. 4

Standard CRRT with D5W Prefilter Method

When standard effluent volumes (20-25 mL/kg/hr) are required for metabolic control but would cause excessive sodium correction:

• Infuse calculated amounts of D5W (5% dextrose in water) prefilter as pre-blood pump to dilute the sodium concentration entering the filter 4
• Calculate D5W rate based on prescribed effluent volume using simplified equations to achieve target sodium correction rate 4
• Monitor sodium levels every 2-4 hours initially to ensure correction does not exceed 8 mEq/L per 24 hours 4
• Adjust D5W rate if initial correction is too rapid—this method can even reverse overcorrection by decreasing sodium levels back down 4

Alternative CRRT Approach

• Reduce effluent volume if metabolic derangements allow, though this may not be feasible when aggressive clearance is needed 4
• Use custom dialysate/replacement fluids with lower sodium concentrations if available, though this is often not practical 4

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Correction Rate Guidelines by Risk Category

Standard Risk Patients

• Target: 4-8 mmol/L per day 1
• Maximum: Never exceed 8 mmol/L in 24 hours 1

High-Risk Patients (cirrhosis, alcoholism, malnutrition, prior encephalopathy)

• Target: 4-6 mmol/L per day 1
• Maximum: Never exceed 8 mmol/L in 24 hours 1

Severe Symptomatic Hyponatremia

• Initial correction: 6 mmol/L over first 6 hours or until symptoms resolve 1
• Subsequent correction: Slow to ensure total does not exceed 8 mmol/L in 24 hours 1

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Management of Overcorrection

If sodium correction exceeds 8 mmol/L in 24 hours during dialysis:

• Immediately stop or modify dialysis prescription (reduce blood flow, change dialysate sodium) 1
• For CRRT patients: Increase D5W prefilter rate to actively lower sodium 4
• Consider desmopressin to promote water retention and slow sodium rise 1
• Switch to D5W infusion if not on dialysis to relower sodium levels 1

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Special Considerations

Uremia as Potential Protection

There is theoretical evidence that uremia may provide some protection against osmotic demyelination during rapid sodium correction, as urea acts as an effective osmole that diffuses slowly across the blood-brain barrier, potentially counteracting fluid shifts out of the brain 5. However, this should never be relied upon as justification for rapid correction—the standard 8 mmol/L per 24-hour limit must still be observed 1, 5

Volume Status Management

• Hypovolemic hyponatremia: May require isotonic saline before or between dialysis sessions, with careful monitoring to avoid excessive sodium correction 1
• Hypervolemic hyponatremia (heart failure, cirrhosis): Fluid restriction to 1-1.5 L/day alongside dialysis; avoid hypertonic saline unless life-threatening symptoms present 1
• Euvolemic hyponatremia (SIADH): Fluid restriction to 1 L/day as adjunct to dialysis 1

Pharmacologic Adjuncts

Tolvaptan should generally be avoided in dialysis patients with severe hyponatremia due to:

• Risk of overly rapid correction (hypernatremia occurred in 1.7% of tolvaptan patients vs 0.8% placebo) 6
• Increased mortality risk in cirrhotic patients (42% vs 38% placebo in heart failure subgroup) 6
• Higher gastrointestinal bleeding risk in cirrhosis (10% vs 2% placebo) 6
• Difficulty controlling correction rate when combined with dialysis 6

If tolvaptan is considered for persistent hyponatremia despite dialysis optimization, start at 15 mg daily with extremely close sodium monitoring (every 2-4 hours initially) 6

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Monitoring Protocol

During Dialysis Session

• Severe symptoms: Check sodium every 2 hours 1
• Mild/no symptoms: Check sodium every 4 hours 1

Between Sessions

• Daily sodium checks until stable in target range 1
• Watch for osmotic demyelination syndrome signs: Dysarthria, dysphagia, oculomotor dysfunction, quadriparesis (typically 2-7 days after rapid correction) 1

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Common Pitfalls to Avoid

• Using standard dialysate sodium (140 mEq/L) in severely hyponatremic patients—this will cause excessive correction 2, 3
• Assuming uremia provides complete protection against osmotic demyelination—it does not 5
• Failing to reduce blood flow rates in conventional HD when managing severe hyponatremia 2, 3
• Not using D5W prefilter in CRRT when standard effluent volumes are needed but would overcorrect sodium 4
• Inadequate monitoring frequency during active correction phase 1
• Ignoring high-risk features (cirrhosis, alcoholism, malnutrition) that require slower correction rates 1