What is the appropriate hemodialysis prescription for a hyponatremic patient, including dialysate sodium concentration, ultrafiltration rate, and management of severe symptomatic hyponatremia?

Hemodialysis Prescription for Hyponatremic Patients

For hyponatremic patients requiring hemodialysis, use a reduced dialysate sodium concentration (130 mEq/L), limit blood flow rate to 50 mL/min, and target a sodium correction rate of no more than 6-8 mEq/L per 24 hours to prevent osmotic demyelination syndrome.

Dialysate Sodium Concentration

• Set dialysate sodium to 130 mEq/L for patients with severe hyponatremia (serum sodium <120 mEq/L) to prevent overly rapid correction during conventional hemodialysis 1
• Standard dialysate sodium (typically 140 mEq/L) will correct serum sodium too rapidly and risks osmotic demyelination syndrome in severely hyponatremic patients 2, 1
• The dialysate sodium concentration should be adjusted daily based on the patient's serum sodium response, gradually increasing toward standard concentrations as serum sodium normalizes 3

Blood Flow Rate and Treatment Duration

• Limit blood flow rate to 50 mL/min during initial hemodialysis sessions to control the rate of sodium correction, achieving approximately 2 mEq/L/hour rise in serum sodium 1
• This reduced blood flow rate allows for necessary volume removal and correction of uremia while maintaining safe sodium correction limits 1
• Monitor serum sodium every 2-4 hours during the initial dialysis treatment to ensure correction does not exceed 6-8 mEq/L in the first 24 hours 4, 1

Alternative: Continuous Venovenous Hemofiltration (CVVH)

• For patients with severe hyponatremia (serum sodium <100-112 mEq/L) and acute kidney injury, continuous venovenous hemofiltration with low-sodium replacement fluid is the preferred modality 2, 3
• CVVH allows precise control of sodium correction rate through adjustment of replacement fluid sodium concentration, which can be modified daily based on serum sodium response 2, 3
• Use single-pool sodium kinetic modeling during CVVH to calculate the exact replacement fluid sodium concentration needed to achieve the desired correction rate 2
• Two methods exist for adjusting replacement fluid: (1) diluting standard replacement fluid with sterile water, or (2) using custom-compounded low-sodium solutions 2

Correction Rate Guidelines

• The absolute maximum sodium correction is 8 mmol/L in any 24-hour period for standard-risk patients 4, 5, 6
• For high-risk patients (cirrhosis, alcoholism, malnutrition, severe hyponatremia), limit correction to 4-6 mmol/L per day with an absolute maximum of 8 mmol/L in 24 hours 4
• Initial target for the first 24 hours should be 6-8 mEq/L rise in serum sodium, not normalization 2, 1
• The goal is to raise sodium to 125-130 mEq/L, not to achieve normal sodium levels acutely 5

Management of Severe Symptomatic Hyponatremia

• For patients with severe neurological symptoms (seizures, altered mental status, coma) requiring urgent dialysis, consider a brief period of 3% hypertonic saline before initiating dialysis to achieve initial 4-6 mEq/L correction over 1-2 hours 4, 5, 6
• Once symptoms improve, transition to controlled hemodialysis or CVVH with low-sodium dialysate/replacement fluid 2, 3
• The combined correction from hypertonic saline plus dialysis must still not exceed 8 mmol/L in 24 hours 4, 6

Monitoring Protocol

• Check serum sodium every 2 hours during the first 6-8 hours of treatment, then every 4-6 hours for the first 24 hours 4, 5
• Monitor for signs of osmotic demyelination syndrome (dysarthria, dysphagia, oculomotor dysfunction, quadriparesis) which typically occur 2-7 days after rapid correction 4
• Track fluid removal carefully, as excessive ultrafiltration can concentrate serum sodium beyond the intended correction rate 2

Volume Status Considerations

• For hypervolemic hyponatremic patients (heart failure, cirrhosis), ultrafiltration goals should be modest initially to avoid concentrating serum sodium too rapidly 2
• Calculate expected sodium rise from ultrafiltration volume and adjust dialysate sodium accordingly to stay within correction limits 2
• In anuric patients, all sodium correction will occur through dialysis, requiring even more careful dialysate sodium selection 3

Critical Pitfalls to Avoid

• Never use standard dialysate sodium (140 mEq/L) in patients with serum sodium <120 mEq/L, as this will cause overly rapid correction and risk osmotic demyelination syndrome 2, 1, 3
• Do not rely on shortened dialysis time alone to limit sodium correction—this approach is unreliable and may leave the patient inadequately dialyzed 1
• Avoid aggressive ultrafiltration in the first dialysis session, as volume removal concentrates serum sodium independent of dialysate sodium concentration 2
• Do not delay necessary dialysis in severely uremic patients out of fear of correcting sodium—use modified dialysate and blood flow rates instead 1, 3