A ventilatory system for providing ventilatory support to a patient without the need for an external source of pressurized drive gas. The ventilatory system comprises a drive pump and a controller such that the drive pump collects ambient air and may pressurize it to a pressure determined by the controller. The controller may signal to the drive pump to pressurize the collected ambient air to a first pressure for delivering ventilatory support to a patient and a second pressure for providing PEEP support to a patient. The controller may signal to the drive pump to deliver a targeted flow and/or volume of collected ambient air to the bellows to provide volumetric ventilatory support during inhalation and a PEEP support during exhalation.