We include adult patients aged 21 to 100 with difficult venous access (history of ≥3 consecutive attempts required for successful cannulation during the current admission) requiring non-emergent venepuncture in the RCT. Each patient undergoes venepuncture over the upper-limb using one of the following: Veinlite® EMS (TransLite®, Texas, USA) (Control), a commercial transillumination device; Prototype-1; Prototype-2; Conventional venepuncture without an assistive device. Outcome measures include: successful cannulation within 2 attempts; duration of venepuncture; subjective user feedback. Fisher's exact and Kruskal-Wallis tests will be performed.