Selecting a primary outcome when designing a randomised clinical trial is essential for comparing trials and interventions, yet studies within the field of peripheral nerve blocks have used various primary outcome, causing an outcome heterogeneity that may ultimately prevent meta-analyses and aggregated results from being performed. Previously used primary outcomes and their associated anticipated effect sizes remain unexamined, which may be of importance for future trials in this area. In this scoping review we aimed to portray the choice of primary outcome(s) and the corresponding anticipated effect size estimates in randomised clinical trials assessing ultrasound-guided peripheral nerve blocks published in major anaesthesia journals. Furthermore, we investigated how sample size calculations are reported. A prospective protocol was registered in the Open Science Framework database (https://osf.io/yntsx).