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