[1] Curtin Univ, Fac Hlth Sci, Prehosp Resuscitat & Emergency Care Res Unit, Perth, WA 6845, Australia
[2] St John Ambulance WA, Perth, WA, Australia
[3] Univ Western Australia, Royal Perth Hosp, Emergency Med, Perth, WA 6009, Australia
[4] Harry Perkins Inst Med Res, Ctr Clin Res Emergency Med, Perth, WA, Australia
[5] Univ Warwick, Warwick Med Sch, Coventry CV4 7AL, W Midlands, England
[6] Heart England NHS Fdn Trust, Birmingham, W Midlands, England
[7] Royal Perth Hosp, Dept Resp & Sleep Med, Perth, WA 6001, Australia