Conducting clinical trials in trauma care is challenging. As new treatments become available, we are faced with the dilemma of how to confirm their effectiveness, and strengthen the evidence base. Randomized controlled trials are the gold standard, but target groups in trauma care are often small and specialized, making the classical approach to trial design difficult. Bayesian designs represent an innovative means of increasing trial efficiency, and conducting trials with more realistic sample sizes. This article examines the design of such trials, using the UK-REBOA Trial as an example.