Methods, systems and devices are described for providing mechanical ventilation support of a patient using an open airway patient interface. The system includes gas delivery circuit and patient interface configurations to optimize performance and efficiency of the ventilation system. A ventilation system may include a ventilator for supplying ventilation gas. A patient interface may include distal end in communication with a patient airway, a proximal end in communication with ambient air, and an airflow channel between the distal end and the proximal end. A gas delivery circuit may be adapted to attach to the patient interface without occluding the patient interface to allow ambient air to flow from outside the patient interface to the patient airway. The ventilation gas may entrain air from ambient and from the patient airway.
