What is the best between needles distance and direction for arteriovenous fistula cannulation in hemodialysis patients? An important yet challenging issue

Arteriovenous fistula (AVF) is the most common and preferred vascular access in patients undergoing hemodialysis (HD), which has revolutionized the prognosis and treatment of HD patients. ¹ Obviously, high quality dialysis is directly associated with lower morbidity, and mortality and improved health and clinical outcomes in HD patients. Although it is clear that incorrect AVF puncture technique is a major factor in developing access recirculation and reducing the adequacy of HD, there is currently no consensus on the best technique for the distance and direction of the needles for AVF cannulation.^1,2

In a study by Dias et al. ¹ has been shown that unidirectional needles placement, with a distance of less than 5 cm, is associated with greater access recirculation and lower dialysis adequacy. They suggested that the best technique is apply needles with a distance of 5 cm or more in opposite directions. This finding was supported by another study. ³ Also, the results of a study by Vahedi et al. ⁴ indicated that with placing AVF needles at a distance of 6 cm in the opposite direction, the lowest access recirculation can be occurred. Contrary to previous findings, a study by Elias et al. ⁵ showed that there is no relationship between needle distance and direction with occurrence of access recirculation and quality of HD. They suggested that the direction of the needles should be decided from case to case, depending on the anatomy of the AVF and the possibility of puncture. On the other hand, another study showed that if needles are placed 2.5 cm apart and unidirectional, HD adequacy will not be affected. They suggested that AVFs can be cannulated with needles at a 2.5 cm distance, without creating access recirculation and impaired effective clearance. ⁶ Reyes ⁷ showed that antegrade placement of arterial needles was associated with better HD adequacy than retrograde placement of vascular needles, however the differences were not statistically significant. Additionally, a study by Parisotto et al. ⁸ found that retrograde positioning of the arterial needle with bevel down orientation is associated with significantly increased failure risk than antegrade positioning with bevel-up. However, another study revealed that there is no significant relationship in terms of HD adequacy between needles at 5 and 7 cm distances as well as anterograde and retrograde directions. ⁹

In sum, considering the importance of using appropriate technique for AVF puncture and also the inconsistency in available evidence regarding the best the needles’ direction and between distance for AVF cannulation, future well designed studies are warranted to establish a widely accepted practice standard for AVF cannulation, with substantial and reliable evidence.