Abstract: An improved system for the control of PEEP in a medical ventilator system having a ventilator and a bellows contained within a bellows canister. A pop-off valve that normally vents excess pressure within the bellows to atmosphere is modified such that its exhaust is vented to a predetermined pressure above atmospheric pressure, such as the PEEP pressure. In the preferred embodiment, that predetermined pressure is the pressure within the ventilator drive gas conduit that transmits the gas from the ventilator to drive the bellows and the exhaust from the pop-off is effectively isolated from that drive gas conduit to avoid contaminating the gas within that drive gas conduit.

Abstract: An all-pneumatic medical ventilator of the volume-limited type is provided with a pneumatically driven drug nebulizer for injecting medication into the patient's breathing circuit in response to a cyclic pressure signal from the ventilator. The nebulizer is driven either directly or indirectly, according to the desired mode of use, from the pressurized oxygen source of the ventilator. In a preferred mode, a given portion of the tidal volume of gas is temporarily withdrawn from the breathing circuit during inhalation and subsequently forcibly returned by way of the nebulizer to the breathing circuit. This takes place during the same inhalation period so that nebulized medication is added to the patient's breathing circuit without changing either the predetermined oxygen concentration or tidal volume of the breathing gas.