A system for providing mechanical ventilation support to a patient and includes a mechanical ventilator. A breathing circuit is pneumatically connected between the mechanical ventilator and a patient connection. An inspiratory check valve is disposed within an inspiratory limb of the breathing circuit. A fresh gas manifold provides fresh gas to the breathing circuit for delivery to the patient. A fresh gas valve is disposed between the fresh gas manifold and the breathing circuit. The fresh gas valve is operable between a first position which directs fresh gas upstream of the inspiratory check valve and a second position that directs fresh gas downstream of the inspiratory check valve. A digital signal processor operates the fresh gas valve selectively between the first position and the second position. A method of ventilating a patient includes introducing a flow of fresh gas into an inspiratory limb of the breathing circuit. A ventilatory support value is sensed with at least one sensor disposed within the breathing circuit. An operational condition of the breathing circuit is identified with a digital signal processor. A fresh gas valve is operated with the digital processor between a first position that directs fresh gas to the inspiratory limb upstream from the inspiratory check valve and a second position that directs the fresh gas downstream from the inspiratory check valve.
