needle direction and distance of arteriovenous fistula cannulation in hemodialysis adequacy; a systematic review and meta-analysis

Introduction: this systematic review and meta-analysis aimed to summarize the evidence regarding the impact of needle direction and distance of arteriovenous fistula (avf) cannulation on kt/v (where k is the dialyzer urea clearance, t, the duration of dialysis, and v, the volume of distribution of urea) and access recirculation (ar) as hemodialysis (hd) adequacy criteria. methods: a comprehensive systematic search was performed on international and domestic electronic databases from the earliest to june 4, 2022 using keywords. analysis was performed in stata software v.14. results: three randomized control trials (rcts) and four non-rct articles were included in the final review. six studies reported the effects of direction, while four mentioned the effects of distances of avf cannulation on outcomes of hd adequacy based on kt/v or ar. results of three non-rct studies showed that retrograde direction decreased kt/v more than antegrade direction (es: 0.44, 95% ci: -0.38 to 1.27). two non-rct studies showed that antegrade decreased ar compared to the retrograde direction (es: -0.64, 95%ci: -1.94 to 0.67). however, the results of two rcts indicated uncertainty about this issue. two of the four studies suggested that a distance of 5 cm or more in arterial and venous needles had greater adequacy than a distance of less than 5 cm. however, other studies did not confirm this finding. conclusion: overall comparison of the results qualitatively and quantitatively indicated uncertainty about the effects of direction and distance of avf cannulation on hd adequacy outcomes. more studies with high-quality designs, such as rcts, are required to better understand and adjudicate the effects of needle direction and distance of avf cannulation on hd adequacy outcomes.