A system for providing mechanical ventilation support to a patient, the system comprising: a mechanical ventilator configured to pneumatically provide mechanical ventilation support to the patient; a breathing circuit pneumatically connected between the mechanical ventilator and a patient connection configured to deliver the mechanical ventilation support to the patient, wherein the breathing circuit comprises an inspiratory limb upstream of the patient connection and an expiratory limb downstream of the patient connection; an inspiratory check valve disposed within the inspiratory limb of the breathing circuit; a fresh gas manifold configured to provide fresh gas to the breathing circuit for delivery to the patient; at least one gas sensor (62, 64) disposed within the breathing circuit, the at least one gas sensor (62, 64) configured to measure a ventilation support value from the gases in the breathing circuit; a fresh gas valve disposed between the fresh gas manifold and the breathing circuit, the fresh gas valve being operable between at least two positions, wherein in a first position the fresh gas valve directs fresh gas through an upstream conduit that provides the fresh gas to the breathing circuit upstream of the inspiratory check valve, and in a second position the fresh gas valve directs the fresh gas through a downstream conduit that provides the fresh gas to the breathing circuit downstream of the inspiratory check valve, wherein when the fresh gas valve is in the second position, during expiration, expired gases combine with the fresh gas to recirculate expired gases to the patient; and a digital signal processor configured to receive the at least one ventilation support value from the at least one gas sensor (62, 64), determines an operational condition of the breathing circuit from at least one of the ventilation support values, and operate the fresh gas valve selectively between the first position and the second position based upon the determined operational condition to provide mechanical ventilation support to the patient. a mechanical ventilator configured to pneumatically provide mechanical ventilation support to the patient; a breathing circuit pneumatically connected between the mechanical ventilator and a patient connection configured to deliver the mechanical ventilation support to the patient, wherein the breathing circuit comprises an inspiratory limb upstream of the patient connection and an expiratory limb downstream of the patient connection; an inspiratory check valve disposed within the inspiratory limb of the breathing circuit; a fresh gas manifold configured to provide fresh gas to the breathing circuit for delivery to the patient; at least one gas sensor (62, 64) disposed within the breathing circuit, the at least one gas sensor (62, 64) configured to measure a ventilation support value from the gases in the breathing circuit; a fresh gas valve disposed between the fresh gas manifold and the breathing circuit, the fresh gas valve being operable between at least two positions, wherein in a first position the fresh gas valve directs fresh gas through an upstream conduit that provides the fresh gas to the breathing circuit upstream of the inspiratory check valve, and in a second position the fresh gas valve directs the fresh gas through a downstream conduit that provides the fresh gas to the breathing circuit downstream of the inspiratory check valve, wherein when the fresh gas valve is in the second position, during expiration, expired gases combine with the fresh gas to recirculate expired gases to the patient; and a digital signal processor configured to receive the at least one ventilation support value from the at least one gas sensor (62, 64), determines an operational condition of the breathing circuit from at least one of the ventilation support values, and operate the fresh gas valve selectively between the first position and the second position based upon the determined operational condition to provide mechanical ventilation support to the patient.