References & formulas

TARGET SODIUM IN CRRT:  The sodium concentration in the CRRT fluids required to achieve the desired correction. To reach this concentration, fluids should be adjusted either by adding/exchanging free water or by adding/exchanging hypertonic sodium, depending on the objective.  

This value represents the net sodium concentration in CRRT, and it is used in the post-filter infusion equation.

Target sodium in bags = (Desired change in [Na] / 1- [e (-Kt/V)] ) + plasma [Na] 

POST FILTER INFUSION RATE : Volume to be infused in post-filter to achieve a new net sodium concentration in the effluent, targeting the desired correction. The infusion may be sodium-free or hypertonic, depending on the clinical objective.  

Post filter Infusion rate =  (([Na] in bags - Target net [Na]  in CRRT ) /  (Target net [Na] in CRRT - [Na] in post filter infusion))  x Total Effluent rate (ml/min) 

• When hyperosmolar citrate is used, the target net [Na] in CRRT is adjusted and applied in the previous formula to account for citrate infusion.
• The post-filter infusion rate should be added to the total effluent volume for the result to be accurate. For example, if 2000 ml/hr is the input for total effluent volume and the result for post-filter infusion is 300 ml/hr, the total effluent to achieve the result should be 2300 ml/hr. 
• Citrate infusion rate is already included in the total effluent volume.

*This formula differs from the original published by Yessayan et al. in that the target net sodium in  CRRT is used instead of the target plasma sodium, which can account for the 10% adjustment mentioned by the original authors.

Yessayan LT, Szamosfalvi B, Rosner MH. Management of dysnatremias with continuous renal replacement therapy. Semin Dial. 2021 Nov;34(6):472-479. 

PMID: 34218456.

Yessayan L, Yee J, Frinak S, Szamosfalvi B. Treatment of severe hyponatremia in patients with kidney failure: role of continuous venovenous hemofiltration with low-sodium replacement fluid. Am J Kidney Dis. 2014 Aug;64(2):305-10. 

PMID: 24792353.

Yessayan L, Yee J, Frinak S, Szamosfalvi B. Continuous Renal Replacement Therapy for the Management of Acid-Base and Electrolyte Imbalances in Acute Kidney Injury. Adv Chronic Kidney Dis. 2016 May;23(3):203-10. 

PMID: 27113697.

Rosner MH, Connor MJ Jr. Management of Severe Hyponatremia with Continuous Renal Replacement Therapies. Clin J Am Soc Nephrol. 2018 May 7;13(5):787-789. 

 PMID: 29463598; 

Neyra JA, Ortiz-Soriano VM, Ali D, Morris PE, Johnston CM. A Multidisciplinary Approach for the Management of Severe Hyponatremia in Patients Requiring Continuous Renal Replacement Therapy. Kidney Int Rep. 2018 Sep 13;4(1):59-66. 

PMID: 30596169;