title: Con-Current versus Counter-Current Dialysate Flow during CVVHD. A Comparative Study for Creatinine and Urea Removal.
abstract: BACKGROUND
  Dialysate fluid connection to the membrane in continuous dialysis may affect solute clearance. Although circuit connections are routinely made counter-current to blood flow in intermittent dialysis, no study has assessed the effect of this dialysate fluid flow direction on removal of small solutes creatinine and urea during treatment using continuous veno-venous haemodialysis (CVVHD).
  
  
  OBJECTIVE
  To assess if dialysate flow direction during CVVHD affects small solute removal.
  
  
  METHODS
  This ethics-approved study recruited a convenience sample of 26 adult ICU patients requiring continuous dialysis to assess urea and creatinine removal for con-current vs. counter-current dialysate flow direction. The circuit was adjusted from continuous veno-venous haemodiafiltration to CVVHD 20 min prior to sampling with no fluid removal. Blood (b) and spent dialysate fluid (f) were taken in both concurrent and counter-current fluid flow at 1 (T1) and 4 (T4) hours with a new treatment. Blood flow was 200 ml/min. Dialysate flow 33 ml/min. Removal of urea and creatinine was expressed as the diafiltrate/plasma concentration ratio: Uf/b and Cf/b respectively. Data lacking normal distribution are presented as median with 25th and 75th interquartile ranges (IQR), otherwise as mean with SD and assessed with the independent t test for paired data. p < 0.5 was considered significant.
  
  
  RESULTS
  Fifteen male patients were included with a median (IQR) age of 67 years (52-75), and APACHE x0399;x0399; score 17 (14-19) with all patients meeting RIFLE criteria 'F'. At both times, the counter-current dialysate flow was associated with higher mean (SD) diafiltrate/plasma concentration ratios: T1 0.87 (0.16) vs. 0.77 (0.10), p = 0.006; T2 0.96 (0.16) vs. 0.76 (0.09), p < 0.001 for creatinine and T1 0.98 (0.09) vs. 0.81 (0.09), p < 0.001; T2 0.99 (0.07) vs. 0.82 (0.08), p < 0.001 for urea.
  
  
  CONCLUSIONS
  Counter-current dialysate flow during CVVHD for ICU patients is associated with an approximately 20% increase in removal of small solutes creatinine and urea. Video Journal Club 'Cappuccino with Claudio Ronco' at http://www.karger.com/?doi=441270.
authors.affiliation: Department of Intensive Care, Austin Hospital, Melbourne Australia and Department of Nephrology and IRRIV, St. Bortolo Hospital, Vicenza, Italy.
authors.forename: Ian
authors.initials: I
authors.lastname: Baldwin
authors.forename: Marie
authors.initials: M
authors.lastname: Baldwin
authors.forename: Nigel
authors.initials: N
authors.lastname: Fealy
authors.forename: Mauro
authors.initials: M
authors.lastname: Neri
authors.forename: Francesco
authors.initials: F
authors.lastname: Garzotto
authors.forename: Jeong Chul
authors.initials: JC
authors.lastname: Kim
authors.forename: Anna
authors.initials: A
authors.lastname: Giuliani
authors.forename: Flavio
authors.initials: F
authors.lastname: Basso
authors.forename: Federico
authors.initials: F
authors.lastname: Nalesso
authors.forename: Alessandra
authors.initials: A
authors.lastname: Brendolan
authors.forename: Claudio
authors.initials: C
authors.lastname: Ronco
mesh_terms: D058186:Acute Kidney Injury / Q000097:blood / Q000473:pathology / Q000628:therapy*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003404:Creatinine / Q000097:blood; D015314:Dialysis Solutions / Q000627:therapeutic use*; D005260:Female; D017583:Hemodiafiltration / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D051436:Renal Insufficiency, Chronic / Q000097:blood / Q000473:pathology / Q000628:therapy*; D016896:Treatment Outcome; D014508:Urea / Q000097:blood
chemical_list: D015314:Dialysis Solutions; D014508:Urea; D003404:Creatinine