"Ventilators are positive pressure devices that deliver regulated volumes of air and supplemental oxygen to patients requiring respiratory support. The concentration of air and oxygen can be adjusted as needed with each breath and with the number of breaths per minute. Pre-hospital ventilators are used during emergency response operations and for ground or air transport. In order to provide responders with information on currently available pre-hospital ventilators, Science Applications International Corporation conducted a comparative assessment of these devices for the System Assessment and Validation for Emergency Responders (SAVER) Program in May 2012."
Department of Homeland Security: https://www.dhs.gov/