Following sample size estimation, we plan to recruit at least 25 000 children over a period of two consecutive weeks including weekends and after-hours across the 30 European countries represented at the European Society of Anaesthesiology Council or part of geographical Europe. The 2-week recruitment period will be chosen by each site commencing on 15 March 2014.The last possible inclusion date will be decided by the Study Steering Committee depending on the recruitment rate. Participating hospitals will be provided with data acquisition sheets that enable anonymous standardized recording of all patients' parameters, which will be used by the local institution to fill in the electronic case report form (eCRF).