1 *Department of Military Anaesthesia and Critical Care, Royal Centre for Defence Medicine, Birmingham, UK †Department of Anaesthesia, Aintree University Hospital NHS Foundation Trust, Liverpool, UK ‡Department of Anaesthesia, Queen Elizabeth Hospitals, Birmingham, UK. §Military Anaesthesia, Academic Department of Military Anaesthesia, Royal Centre for Defence Medicine, Birmingham, UK ∥Department of Anaesthesia, Derriford Hospital, Plymouth Hospitals NHS Trust, Plymouth, UK.