Effects of dialysate flow configurations in continuous renal replacement therapy on solute removal: computational modeling.
OBJECTIVE
Continuous renal replacement therapy (CRRT) is commonly used for critically ill patients with acute kidney injury. During treatment, a slow dialysate flow rate can be applied to enhance diffusive solute removal. However, due to the lack of the rationale of the dialysate flow configuration (countercurrent or concurrent to blood flow), in clinical practice, the connection settings of a hemodiafilter are done depending on nurse preference or at random.


METHODS
In this study, we investigated the effects of flow configurations in a hemodiafilter during continuous venovenous hemodialysis on solute removal and fluid transport using computational fluid dynamic modeling. We solved the momentum equation coupling solute transport to predict quantitative diffusion and convection phenomena in a simplified hemodiafilter model.


RESULTS
Computational modeling results showed superior solute removal (clearance of urea: 67.8 vs. 45.1 ml/min) and convection (filtration volume: 29.0 vs. 25.7 ml/min) performances for the countercurrent flow configuration. Countercurrent flow configuration enhances convection and diffusion compared to concurrent flow configuration by increasing filtration volume and equilibrium concentration in the proximal part of a hemodiafilter and backfiltration of pure dialysate in the distal part. In clinical practice, the countercurrent dialysate flow configuration of a hemodiafilter could increase solute removal in CRRT. Nevertheless, while this configuration may become mandatory for high-efficiency treatments, the impact of differences in solute removal observed in slow continuous therapies may be less important. Under these circumstances, if continuous therapies are prescribed, some of the advantages of the concurrent configuration in terms of simpler circuit layout and simpler machine design may overcome the advantages in terms of solute clearance.


CONCLUSIONS
Different dialysate flow configurations influence solute clearance and change major solute removal mechanisms in the proximal and distal parts of a hemodiafilter. Advantages of each configuration should be balanced against the overall performance of the treatment and its simplicity in terms of treatment delivery and circuit handling procedures.
Department of Nephrology, Dialysis and Transplantation, San Bortolo Hospital, Vicenza, Italy.
Jeong Chul
JC
Kim
Dinna
D
Cruz
Francesco
F
Garzotto
Manish
M
Kaushik
Catarina
C
Teixeria
Marie
M
Baldwin
Ian
I
Baldwin
Federico
F
Nalesso
Ji Hyun
JH
Kim
Eungtaek
E
Kang
Hee Chan
HC
Kim
Claudio
C
Ronco
D058186:Acute Kidney Injury / Q000097:blood / Q000503:physiopathology / Q000628:therapy*; D003198:Computer Simulation; D018481:Convection; D016638:Critical Illness / Q000628:therapy*; D004058:Diffusion; D015312:Hemodialysis Solutions / Q000737:chemistry; D018056:Hemorheology; D006801:Humans; D008962:Models, Theoretical; D006435:Renal Dialysis / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data*; D013813:Therapy, Computer-Assisted; D014508:Urea / Q000097:blood; D014882:Water-Electrolyte Balance
D015312:Hemodialysis Solutions; D014508:Urea