Loss of antimicrobial effect of trisodium citrate due to 'lock' spillage from haemodialysis catheters

Due to its reported antimicrobial effects, hypertonic citrate (46.7%) is a widely used catheter lock solution, but following instillation, citrate inevitably spills into the systemic circulation. This process is mainly driven by hydraulic effects during instillation and density differences between blood and lock solution. Hence, in haemodialysis catheters, intra-luminal citrate concentration ranges from 0% (at the tip in catheters with side holes), 3% (between the side holes and the highest point of the catheter) to 46.7% (at the Luer end) with possible differences in antimicrobial effects. We investigated in vitro the antimicrobial effect of pure citrate 46.7%, citrate 46.7% diluted with saline and blood to a net concentration of 3% (=citrate 3%), and of citrate-free blood, simulating in vivo conditions in different catheter sections.