A system for providing mechanical ventilation support to a patient and includes a mechanical ventilator (26). A breathing circuit (14) is pneumatically connected between the mechanical ventilator (26) and a patient connection (22). An inspiratory check valve (30) is disposed within an inspiratory limb (16) of the breathing circuit (14). A fresh gas manifold (38) provides fresh gas to the breathing circuit (14) for delivery to the patient. A fresh gas valve (52) is disposed between the fresh gas manifold (38) and the breathing circuit (14). The fresh gas valve (52) is operable between a first position which directs fresh gas upstream of the inspiratory check valve (30) and a second position that directs fresh gas downstream of the inspiratory check valve (30). A digital signal processor (44) operates the fresh gas valve (52) 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 (16) of the breathing circuit (14). A ventilatory support value is sensed with at least one sensor (62, 64) disposed within the breathing circuit (14). An operational condition of the breathing circuit (14) is identified with a digital signal processor (44). A fresh gas valve (52) is operated with the digital processor (44) between a first position that directs fresh gas to the inspiratory limb (16) upstream from the inspiratory check valve (30) and a second position that directs the fresh gas downstream from the inspiratory check valve (30).
