[1] Great Ormond St Hosp Children NHS Fdn Trust, Dept Anaesthesia, London WC1N 3JH, England
[2] Karolinska Univ Hosp, Dept Perioperat Med & Intens Care, Stockholm, Sweden
[3] Karolinska Inst, Dept Physiol & Pharmacol, Sect Anesthesiol & Intens Care Med, Stockholm, Sweden
[4] Univ Coll London Hosp NHS Fdn Trust, Dept Anaesthesia, London, England