Extreme hyponatremia poses a management challenge when performing hemodialysis. Most conventional dialysis machines have a lower limit for sodium concentration of 130 mml/L. Continuous renal replacement therapy (CRRT) solutions on the other hand, generally contain 140 mmol/L. When performing CRRT in cases of extreme hyponatremia, a lower dialysate sodium is desired to prevent inappropriately rapid rises in serum sodium. The following calculators provides some guidance on the selecting a replacement fluid volume and sodium composition based in part from this publication.
Example: A 50 year-old woman presents with severe AKI and sodium 100 mmol/L. It was desirable to reduce the blood returning to the patient to maximum sodium concentratrion of 108 mmol/L. If 1L/hour of dilaysate was chosen for CRRT containing 140 mmol/L of sodium, then the calculator below suggests that 0.97L/hour of 1/2NS (sodium concentration 75 mmol/L) would be required. If D5W was selected (sodium concentration 0 mmol/L), then 0.296L would be required.
Reference: Management of Severe Hyponatremia with Continuous Renal Replacement Therapies. Clin J Am Soc Nephrol. 2018 May 7;13(5):787-789. doi: 10.2215/CJN.13281117.