Preventing adverse events during paediatric cancer treatment: protocol for a multi-site hybrid randomised controlled trial of catheter lock solutions (the CLOCK trial).

INTRODUCTION: Central venous access devices (CVADs) are commonly used for the treatment of paediatric cancer patients. Catheter locking is a routine intervention that prevents CVAD-associated adverse events, such as infection, occlusion and thrombosis. While laboratory and clinical data are promising, tetra-EDTA (T-EDTA) has yet to be rigorously evaluated or introduced in cancer care as a catheter lock. METHODS AND ANALYSIS: This is a protocol for a two-arm, superiority type 1 hybrid effectiveness-implementation randomised controlled trial conducted at seven hospitals across Australia and New Zealand. Randomisation will be in a 3:2 ratio between the saline (heparinised saline and normal saline) and T-EDTA groups, with randomly varied blocks of size 10 or 20 and stratification by (1) healthcare facility; (2) CVAD type and (3) duration of dwell since insertion. Within the saline group, there will be a random allocation between normal and heparin saline. Participants can be re-recruited and randomised on insertion of a new CVAD. Primary outcome for effectiveness will be a composite of CVAD-associated bloodstream infections (CABSI), CVAD-associated thrombosis or CVAD occlusion during CVAD dwell or at removal. Secondary outcomes will include CABSI, CVAD-associated-thrombosis, CVAD failure, incidental asymptomatic CVAD-associated-thrombosis, other adverse events, health-related quality of life, healthcare costs and mortality. To achieve 90% power (alpha=0.05) for the primary outcome, data from 720 recruitments are required. A mixed-methods approach will be employed to explore implementation contexts from the perspective of clinicians and healthcare purchasers. ETHICS AND DISSEMINATION: Ethics approval has been provided by Children's Health Queensland Hospital and Health Service Human Research Ethics Committee (HREC) (HREC/22/QCHQ/81744) and the University of Queensland HREC (2022/HE000196) with subsequent governance approval at all sites. Informed consent is required from