References & Formulas

Teixeira JP, Neyra JA, Tolwani A. Continuous KRT: A Contemporary Review.  Clin J Am Soc Nephrol. 2023 Feb 1;18(2):256-269. 

PMID: 35981873

Griffin BR, Liu KD, Teixeira JP. Critical Care Nephrology: Core  Curriculum 2020. Am J Kidney Dis. 2020 Mar;75(3):435-452. 

PMID: 31982214

Tandukar S, Palevsky PM. Continuous Renal Replacement Therapy: Who,  When, Why, and How. Chest. 2019 Mar;155(3):626-638. 

PMID: 30266628

Ideal time, expected down time and measured effluent saturation are modifiable variables that affect delivered dose.

Claure-Del Granado R, et al. Toward the optimal dose metric in  continuous renal replacement therapy. Int J Artif Organs. 2012  Jun;35(6):413-24.

PMID: 22466995

Filtration Fraction (FF) = Total Ultrafiltration Rate / (Plasma Flow Rate + Pre-Filter Replacement Fluid Rate)  

Total Ultrafiltration Rate (ml/hr) = Pre-Filter Replacement Fluid Rate (ml/hr) + Post-Filter Replacement Fluid Rate (ml/hr) + Fluid Removal Rate (ml/hr) 

Plasma Flow Rate (ml/hr) = Blood Flow Rate (ml/min) X 60 (min/hr) X (1-HCT)

When using Pre-Filter Replacement Fluid the CRRT dose is diluted

Dilution Factor = Plasma Flow Rate (ml/hr) / [Plasma Flow Rate (ml/hr) + Pre-Filter Replacement Fluid Rate (ml/hr)] 

Plasma Flow Rate (ml/hr) = Blood Flow Rate (ml/min) X 60 (min/hr) X (1-HCT)

Flow fraction is a concept extrapolated from home hemodialysis literature and is simply the:  Dialysate flow (ml/hr)/ Blood flow (ml/hr) .  

When using diffusion the flow fraction will be the main determinant of the effluent saturation. A flow fraction of 0.4 or lower will saturate the effluent to a 100%

Theoretical  small solute effluent saturation with the given prescription: 

Convective effluent saturation= 100% 

Diffusive effluent saturation = (Calculated diffusive urea clearance  / prescribed diffusive urea clearance) * 100

Calculated diffusive urea clearance:  estimated as a function of blood flow, dialysate flow and a membrane permeability area coefficient (koA) of 500 ml/min  using the Michaels/Depner model.

Michaels AS. Operating parameters and performance criteria for  hemodialyzers and other membrane-separation devices. Trans Am Soc Artif  Intern Organs. 1966;12:387-92. 

PMID: 5960730.

Depner TA, et al.  Dialyzer performance in the HEMO Study: in vivo K0A and true blood flow  determined from a model of cross-dialyzer urea extraction. ASAIO J. 2004;50(1):85-93.

PMID: 14763497.

Prescribed dose = Total effluent volume / weight

Delivered dose =  (prescribed dose) x (dilution factor) x (expected time - downtime / expected time) x (theoretical OR measured effluent saturation) 

Delivered percentage = (delivered dose / prescribed dose ) x 100

Clark WR, Leblanc M, Ricci Z, Ronco C. Quantification and Dosing of  Renal Replacement Therapy in Acute Kidney Injury: A Reappraisal. Blood  Purif. 2017;44(2):140-155. 

PMID: 28586767.

Claure-Del Granado R, et al. Effluent volume in continuous renal  replacement therapy overestimates the delivered dose of dialysis. Clin J  Am Soc Nephrol. 2011 Mar;6(3):467-75. 

 PMID: 21115626

Claure-Del Granado R, et al. Toward the optimal dose metric in  continuous renal replacement therapy. Int J Artif Organs. 2012  Jun;35(6):413-24.

PMID: 22466995

Urea clearance = (delivered dose x weight) / 60 

Urea KT = urea clearance x ideal time

Urea KT/V = urea KT / (weight x 0.5 + excess volume)