aCentre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London

bIntensive Care Unit, Guy's and St Thomas’ NHS Foundation Trust

cDepartment of Anaesthetics, Royal Brompton and Harefield, part of Guy's and St. Thomas’ NHS Foundation Trust, London, UK

dDepartment of Anesthesiology, University Medical Center of Göttingen, Göttingen, Germany

eNuffield Division of Anaesthetics, University of Oxford, Oxford, UK

fDepartment of Biomechanics, University of Nebraska Omaha, Omaha, Nebraska, USA

Correspondence to Dr Luigi Camporota, Centre for Human and Applied Physiological Sciences, School of Basic and Medical Biosciences, King's College London, London SE1 1UL, UK. E-mail: [email protected]