1 Department of Anaesthesia, Critical Care and Pain Medicine, University of Edinburgh, Chancellor's Building, Little France, Edinburgh, United Kingdom.
2 Department of Neurosurgery & Centre for Clinical Brain Sciences, University of Edinburgh & NHS Lothian, Western General Hospital, Edinburgh EH4 2XU, United Kingdom.
3 Centre for Clinical Brain Sciences, University of Edinburgh & NHS Lothian, Western General Hospital, Edinburgh EH4 2XU, United Kingdom.