1. Department of Anaesthesia and Critical Care, Harefield Hospital, Royal Brompton and Harefield Hospitals, London UB9 6JH, UK
2. Harefield Hospital, Royal Brompton and Harefield Hospitals, London UB9 6JH, UK
3. School of Medicine, University of Zagreb, 10000 Zagreb, Croatia
4. Division of Anaesthetics, Pain Medicine and Intensive Care, Department of Surgery and Cancer, Imperial College London, London SW7 2BX, UK