1 Paediatric Intensive Care Unit, Great Ormond Street Hospital for Children NHS Foundation Trust and NIHR Biomedical Research Centre, London WC1N 3JH, UK; University College London Great Ormond Street Institute of Child Health, London, UK; Children's Acute Transport Service, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK. Electronic address: mark.peters@ucl.ac.uk.
2 Clinical Trials Unit, Intensive Care National Audit & Research Centre, London, UK.