Single needle hemodialysis: is the past the future?

Whereas the usual way to gain access to the vascular bed for hemodialysis is by inserting two needles, an alternative option based on the introduction of only one needle has been available for several decades. Although single needle hemodialysis gradually lost popularity in the early nineties of last century, this option now seems to make a come-back, with the current change in patient mix towards more elderly and cardio-vascular disease and the appearance of more flexible hardware. Single needle hemodialysis offers several advantages, such as the possibility to puncture small or maturing access systems, a decrease in number of punctures with less potential access damage and subsequent complications, the avoidance of central vein catheter use, and an improved quality of life by reducing puncture-related pain, stress and complications. The main drawback is recirculation which however can be overcome (if considered necessary) by making dialysis somewhat longer and in addition has more impact on removal of small water soluble compounds than on clearance of the more toxic difficult to remove solutes (middle molecules and protein bound compounds). Effective dialyzer blood flow with single needle dialysis cannot be much higher than 300 mL/min, which however also offers advantages by making short dialysis sessions less feasible and thus reducing the likelihood of intradialytic blood pressure falls, organ stunning and other negative outcomes of shorter dialysis. Direct outcome comparisons between single and double needle dialysis are not available but indirect data suggest no differences, in as far as efficient enough access perfusion can keep dialyzer blood flow adequate. The single needle method seems especially suited for the elderly and for home hemodialysis. Recent technological improvements have made the system more accessible and adequate, but further studies are needed to assess with modern methodologies the clearance kinetics of these systems, which could emanate in further technological fine-tuning.