A gas flow-focusing device (FFD) may include a cylindrical body that may include a funneling part to receive exhaled CO2-enriched air, and a CO2 sampling part. The CO2 sampling part and the funneling part are in fluid flow communication. The CO2 sampling part may include a CO2 sampling chamber to accept the CO2-enriched air, and a CO2 sampling tube to sample the CO2-enriched air. The funneling part and the CO2 sampling part may structurally form between them a ring-shaped gas chamber to contain a pressurized propellant gas, and a hollow channel in order to channel the pressurized propellant gas from the gas chamber to the CO2 sampling chamber. The gas chamber may include a gas intake opening through which propellant gas may fill the gas chamber. A prong-free cannula (PFC) may include two FFDs for sampling CO2, and a plurality of apertures for providing, there through, oxygen.