title: The measurement of hemodialysis access blood flow by a conductivity step method.
abstract: OBJECTIVE
  Measurement of blood flow rate (Qa) is used to monitor dialysis access, AV fistulas, and grafts. Indicator dilution measurements of the recirculation (R) induced by reversal of hemodialysis blood lines are commonly used. This plus the dialysis circuit flow (Qb) allows calculation of Qa. R also changes the conductivity, which can be measured by a conductivity cell in the spent dialysate. The change in conductivity caused by line reversal should vary with Qa. A methodology for Qa measurement utilizing this conductivity step is proposed. This study compares conductivity step methodology against the reference method of ultrasound dilution (Qa-Trans).
  
  
  METHODS
  This was an open diagnostic test study in a single academic hospital setting involving 15 hemodialysis-dependent patients. Each was studied over four hemodialysis treatments. During each treatment, two pairs of Qa measurements (conductivity step and Trans) were made. Pre- and postdialysis sodium levels were also measured.
  
  
  RESULTS
  Average Qa-conductivity step was 1040 ml/min. Average Qa-Trans was 1030 ml/min. The difference was NS. The data pairs showed mean difference of 1.3 +/- 17% (SD). The SD indicates a relatively large variation between data pairs. There was significant linear correlation between the Qa-conductivity step and Qa-Trans results (r = 0.91, P < 0.001). Serum sodium rose slightly but significantly over dialysis (P < 0.001).
  
  
  CONCLUSIONS
  Qa measurement by conductivity step may be an acceptable alternative to ultrasound dilution methodology. Care must be taken to prevent salt loading when the conductivity step is used.
authors.affiliation: London Health Sciences Centre and the University of Western Ontario, London, Ontario, Canada. robert.lindsay@lhsc.on.ca
authors.forename: Robert M
authors.initials: RM
authors.lastname: Lindsay
authors.forename: Shih-Han S
authors.initials: SH
authors.lastname: Huang
authors.forename: Jan
authors.initials: J
authors.lastname: Sternby
authors.forename: Thomas
authors.initials: T
authors.lastname: Hertz
mesh_terms: D001166:Arteriovenous Shunt, Surgical; D015415:Biomarkers / Q000097:blood; D001783:Blood Flow Velocity; D019917:Blood Vessel Prosthesis Implantation; D015314:Dialysis Solutions / Q000737:chemistry*; D004553:Electric Conductivity; D005260:Female; D006785:Hospitals, University; D006801:Humans; D007201:Indicator Dilution Techniques; D008297:Male; D009864:Ontario; D011237:Predictive Value of Tests; D012039:Regional Blood Flow; D006435:Renal Dialysis; D012964:Sodium / Q000097:blood; D014463:Ultrasonography
chemical_list: D015415:Biomarkers; D015314:Dialysis Solutions; D012964:Sodium