Squadrone V, Coha M, Cerutti E, Schellino MM, Biolino P, Occella P, Belloni G, Vilianis G, Fiore G, Cavallo F, Ranieri VM. JAMA. 2005 Feb 2;293(5):589-95
Randomised, controlled, unblinded study on 209 patients randomyl assigned to receive oxygen or oxygen plus CPAP via helmet. Primary end point was incidence of endotracheal intubation. Authors conclude that CPAP via helmet 'may decrease the incidence of endotracheal intubation' in this scenario.
Link to abstract.