1. Intensive Care Unit, Western General Hospital, Crewe Road South, Edinburgh EH4 2XU, UK
2. Intensive Care Unit, Royal Infirmary of Edinburgh, 51 Little France Crescent, Edinburgh EH16 4SA, UK
3. Edinburgh Critical Care Research Group (ECCRG), The University of Edinburgh, The Royal Infirmary of Edinburgh, 51 Little France Cres., Edinburgh EH16 4SA, UK