A system (100) for sampling exhaled breath and for supply of a gas, the system (100) comprising: a gas delivery cannula (102) comprising at least one nasal prong (108,110) for insertion into a nostril, the nasal prong (108,110) comprising a distal end (108a,110a) an exhaled breath sampling cannula (111) for insertion into the nostril, the exhaled breath sampling cannula (111) comprising a distal end (112) and a connector (122) for coupling the gas delivery cannula (102) to the exhaled breath sampling cannula (111), such that the distal end (112) of the exhaled breath sampling cannula (111) is disposed deeper in the nostril than the distal end (108a,110a) of the nasal prong (108,110), to reduce dilution of sampled exhaled breath by delivered gas. The connector is configured to facilitate adjustability of an insertion depth of the exhaled breath sampling cannula (111) into said nostril.
