The influence of between‐needle cannulation distance on the efficacy of hemodialysis treatments

Abstract

There is a belief that there should be a minimum of 5 cm between two cannulating needles of an arteriovenous fistula. This study examined the effect of reduction of space between needles from 5 cm to 2.5 cm on access recirculation, the measurement of access blood flow rate (by indicator dilution technology), and dialysis efficiency (by effective ionic dialysance). Twelve patients were studied, with half having their dialysis needles placed 2.5 cm apart for five consecutive dialysis treatments followed by placing needles 5 cm apart for a further five consecutive treatments. The other half initiated with 5 cm followed by 2.5 cm distance for a similar number of treatments. All 120 dialyses had successful cannulations with access recirculation excluded. Access blood flow (Qa mL/min) measurement was attempted for each patient twice, with each of the two needle positions. The Qa with needles 2.5 cm apart was 1310.95 ± 525.7 mL/min (M ± SD, n = 21) and was 1001.0 ± 240.4 mL/min when 5 cm apart (n = 22) (p = 0.014). There was a correlation between these two sets of Qa values (r = 0.554; p = 0.011). The effective ionic dialysance values obtained with needles 2.5 cm or 5 cm apart were similar and correlated strongly (r = 0.71; p = 0.000). Hemodialysis treatments using arteriovenous fistulae and two needles as close as 2.5 cm apart are possible without access recirculation and impairment of clearance. Indicator dilution access blood flow measurements are not recommended under these circumstances.