Effluent volume in continuous renal replacement therapy overestimates the delivered dose of dialysis.
OBJECTIVE
Studies examining dose of continuous renal replacement therapy (CRRT) and outcomes have yielded conflicting results. Most studies considered the prescribed dose as the effluent rate represented by ml/kg per hour and reported this volume as a surrogate of solute removal. Because filter fouling can reduce the efficacy of solute clearance, the actual delivered dose may be substantially lower than the observed effluent rate.


METHODS
Data were examined from 52 critically ill patients with acute kidney injury (AKI) requiring dialysis. All patients were treated with predilution continuous venovenous hemodiafiltration (CVVHDF) and regional citrate anticoagulation. Filter performance was monitored during the entire course of therapy by measuring blood urea nitrogen (BUN) and dialysis fluid urea nitrogen (FUN) at initiation and every 12 hours. Filter efficacy was assessed by calculating FUN/BUN ratios every 12 hours of filter use. Prescribed urea clearance (K, ml/min) was determined from the effluent rate. Actual delivered urea clearance was determined using dialysis-side measurements.


RESULTS
Median daily treatment time was 1413 minutes (1260 to 1440) with a total effluent volume of 46.4 ± 17.4 L and urea mass removal of 13.0 ± 7.6 mg/min. Prescribed clearance overestimated the actual delivered clearance by 23.8%. This gap between prescribed and delivered clearance was related to the decrease in filter function assessed by the FUN/BUN ratio.


CONCLUSIONS
Effluent volume significantly overestimates delivered dose of small solutes in CRRT. To assess adequacy of CRRT, solute clearance should be measured rather than estimated by the effluent volume.
Division of Nephrology and Hypertension, Department of Medicine, University of California-San Diego, San Diego, California, USA. rmehta@ucsd.edu
Rolando
R
Claure-Del Granado
Etienne
E
Macedo
Glenn M
GM
Chertow
Sharon
S
Soroko
Jonathan
J
Himmelfarb
T Alp
TA
Ikizler
Emil P
EP
Paganini
Ravindra L
RL
Mehta
D000046:Academic Medical Centers; D058186:Acute Kidney Injury / Q000097:blood / Q000628:therapy*; D000328:Adult; D000925:Anticoagulants / Q000627:therapeutic use; D001806:Blood Urea Nitrogen; D016009:Chi-Square Distribution; D002951:Citrates / Q000627:therapeutic use; D016638:Critical Illness; D005260:Female; D017583:Hemodiafiltration / Q000295:instrumentation; D015312:Hemodialysis Solutions / Q000737:chemistry / Q000627:therapeutic use*; D006801:Humans; D008297:Male; D008567:Membranes, Artificial; D008875:Middle Aged; D008954:Models, Biological; D013997:Time Factors; D016896:Treatment Outcome; D014481:United States
D000925:Anticoagulants; D002951:Citrates; D015312:Hemodialysis Solutions; D008567:Membranes, Artificial