A nasal cannula assembly includes a breathing gas supply lumen assembly splitting into a first inspiratory gas lumen and a second inspiratory gas lumen. An inspiratory gas nasal end portion is in fluid communication with the first inspiratory gas lumen and a second inspiratory gas lumen. The inspiratory gas nasal end portion has a pair of nasal prongs extending outwardly therefrom. An expiratory gas assembly splits into a first expiratory gas lumen and a second expiratory gas lumen. An expiratory gas nasal end portion is in fluid communication with the first expiratory gas lumen and a second expiratory gas lumen. A passage is disposed across the inspiratory nasal end portion from the pair of nasal prongs. The passage provides fluid communication between the inspiratory nasal end portion and the expiratory nasal end portion.
