Benger, Jonathan, Voss, Sarah, Coates, David, Greenwood, Rosemary, Nolan, Jerry, Rawstorne, Steven, Rhys, Megan, Thomas, Matthew, "Randomised comparison of the effectiveness of the laryngeal mask airway supreme, i-gel and current practice in the initial airway management of prehospital cardiac arrest (REVIVE-Airways): A feasibility study research protocol", BMJ Open, 2013