This German study, published in Resuscitation in 2011, collected data regarding prehospital endotracheal intubations performed by physicians from a variety of specialties in both helicopter and ground EMS.
Of 276 patients analyzed, 86.9% were intubated on the first pass, 9.8% required 2 attempts, 1.1% required 3 attempts, and 1.4% could not be intubated.
The factors most commonly associated with difficult intubation were obesity, short neck, and limited space on scene. Limited space on scene more than doubled the probability of difficult intubation.
Full-text pdf for this article is available here (secure area limited to ADHB staff only – ADHB has online subscription access to this journal via the Philson Library at The University of Auckland School of Medicine)