[1] Univ Glasgow, Sch Med Dent & Nursing, Glasgow, Lanark, Scotland
[2] Univ Glasgow, Sch Med Dent & Nursing, Acad Unit Anaesthesia Pain & Crit Care Med, Glasgow, Lanark, Scotland
[3] Golden Jubilee Natl Hosp, Cardiothorac Crit Care, Glasgow, Lanark, Scotland
[4] Glasgow Royal Infirm, Intens Care Unit, Glasgow, Lanark, Scotland
[5] NHS Greater Glasgow & Clyde, Carers Ctr, Glasgow, Lanark, Scotland
[6] NHS Greater Glasgow & Clyde, Clin Phys, Glasgow, Lanark, Scotland
[7] VA Ann Arbor Hlth Syst, Ctr Clin Management Res, Ann Arbor, MI USA
[8] Univ Michigan, Dept Internal Med, Div Pulm & Crit Care, Ann Arbor, MI 48109 USA