[1] Univ Copenhagen, Ctr Head & Orthopaed, Dept Anaesthesia, Rigshosp, Copenhagen, Denmark
[2] Nordsjaellands Hosp, Dept Anaesthesiol & Intens Care, Hillerod, Denmark
[3] Univ Copenhagen, Dept Clin Med, Copenhagen, Denmark
[4] Univ Hosp Bonn, Dept Anaesthesiol & Intens Care, Bonn, Germany
[5] Danish Air Ambulance, Aarhus, Denmark
[6] Univ Copenhagen, Ctr Head & Orthopaed, Dept Anaesthesia, Rigshosp, Inge Lehmanns Vej 6, DK-2100 Copenhagen, Denmark