Hemodialysis catheter lock therapy beyond composition: How tip design and fluid dynamics shape delivered exposure, efficacy, and safety.

Maintaining tunneled dialysis catheter patency while reducing catheter-related bloodstream infection, dysfunction, and unintended systemic exposure remains a persistent challenge in vascular-access care. Comparative studies have established that lock composition matters, particularly for infection prevention, yet they have largely evaluated lock therapy as a nominal formulation rather than as a delivered intraluminal intervention. This review argues that the biological effect ultimately achieved within the catheter may also be shaped by catheter architecture and lock-handling variables, including tip design, side-hole geometry, true luminal volume, fill ratio, lock density, interdialytic dwell, and aspiration practice. By integrating randomized trials, meta-analyses, spillage studies, fluid-dynamic data, biofilm observations, and contemporary vascular-access literature, we propose delivered exposure as a conceptual pharmacomechanical framework for interpreting why infection, patency, and systemic safety do not always move in parallel. Importantly, this framework does not contend that catheter design has already been proven to determine hard clinical outcomes independently of lock composition, nor that delivered exposure is a validated bedside metric. Rather, it offers a more explicit way to understand residual heterogeneity across studies, especially when formulation-level randomization leaves mechanically relevant descriptors unreported. Re-reading the lock literature through this lens suggests that future studies should better characterize the intervention actually delivered by reporting key device- and procedure-level variables, while clinicians should interpret lock performance within the broader catheter-care ecosystem that includes hub management, filling technique, and dysfunction phenotype. This perspective aims to refine, rather than overturn, current evidence and to support a more rigorous and clinically informative evaluation of lock therapy.