[1] Birmingham Childrens Hosp, Paediat Intens Care Unit, Birmingham B4 6NH, W Midlands, England
[2] Univ Birmingham, Sch Clin & Expt Med, Coll Med & Dent Sci, Birmingham B15 2TT, W Midlands, England
[3] Boston Childrens Hosp, Dept Neurol, Boston, MA 02115 USA
[4] Boston Childrens Hosp, Dept Anaesthesia, Boston, MA 02115 USA
[5] Harvard Univ, Sch Med, Boston, MA 02115 USA
[6] Univ Leeds, Sch Med, Leeds Inst Cardiovasc & Metab Med, Epidemiol, Leeds LS2 9JT, W Yorkshire, England
[7] Univ Leicester, Perinatal & Paediat Epidemiol Dept Hlth Sci, Coll Med Biol Sci & Psychol, Leicester LE1 6TP, Leics, England
[8] Univ Leeds, Leeds Inst Cardiovasc & Metab Med, Sch Med, Leeds LS2 9JT, W Yorkshire, England
[9] Birmingham Childrens Hosp, Res & Dev, Birmingham B4 6NH, W Midlands, England