Rob Mac Sweeney1, Daniel F McAuley2. 1. Regional Intensive Care Unit, Royal Victoria Hospital, Belfast, Northern Ireland, UK. 2. Regional Intensive Care Unit, Royal Victoria Hospital, Belfast, Northern Ireland, UK; Centre for Experimental Medicine, Queen's University Belfast, Wellcome-Wolfson Institute for Experimental Medicine, Belfast BT9 7AE, Northern Ireland, UK. Electronic address: d.f.mcauley@qub.ac.uk.