Association of helicopter transportation and improved mortality for patients with major trauma in the northern French Alps trauma system: an observational study based on the TRENAU registry. - Ageron FX; Debaty G; Savary D; Champly F; Albasini F; Usseglio P; Vallot C; Galvagno S; Bouzat P (Scandinavian journal of trauma, resuscitation and emergency medicine, 2020)