aWarwick Medical School, University Hospitals Coventry and Warwickshire NHS Trust, Coventry, UK

bUniversity Hospitals Coventry and Warwick NHS Trust, Coventry, UK

cRoy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA

Correspondence to Dr Adam J. Boulton, Critical Care Unit, University Hospitals Coventry and Warwickshire NHS Trust, Coventry CV2 2DX, UK. E-mail: [email protected]