Tonnelier JM, Prat G, Nowak E, Goetghebeur D, Renault A, Boles JM, L'her E. Intensive Care Med. 2003 Nov;29(11):2077-80
Prospective pilot study on 11 adult patients with acute hypoxemic respiratory failure, treated with helmet CPAP, matched with 11 control patients treated with standard face mask. Primary end points were improvements of gas exchanges and clinical parameters of respiratory distress. Authors conclude the helmet is an 'efficient alternative' to face mask treatment 'even in cases of severe respiratory acidosis and hypercapnia'.
Link to abstract.