Impact of a multifaceted early mobility intervention for critically ill children – the PICU Up! trial: study protocol for a multicenter stepped-wedge cluster randomized controlled trial Razvan AzamfireiColleen MennieVictor D. DinglasArooj FatimaElizabeth ColantuoniAyse P. GursesMichele C. BalasDale M. NeedhamSapna R. Kudchadkar Trials March 2023 DOI PDF URL