1 Department of Anaesthesia, Great Ormond Street Hospital, London, UK. Electronic address: christa.morrison@doctors.org.uk.
2 Department of Anaesthesia, Great Ormond Street Hospital, London, UK.
3 Department of Anaesthesia, National Hospital for Neurology and Neurosurgery, London, UK.
4 Department of Anaesthesia and Perioperative Medicine, University College London Hospitals, London, UK; University College London Hospitals and Great Ormond Street Hospital National Institute of Health Research Biomedical Research Centres, London, UK.