On-airway sampling line is a kind of elongated sampling line, which is used to obtain sample gas in bronchia intubation occasions. One side of the sampling line connects to a T-fitting, and the T-fitting is in series with the anesthesia machine or breathing machine pipeline. Meanwhile, the other side of the sampling line is connected to a water trap, and the water trap is joined to the external sidestream ETCO2 module produced by our company. The on-airway sampling line is a special sampling line. It is invented by our company only for ETCO2 sampling. Compared with the conventional connection line, the inside diameter of our on-airway sampling line is much smaller. Because of this, people can quickly get CO2 waveform and data from the monitor, and also avoid the loss of CO2 waveform peak (ETCO2 values). Furthermore, the flexibility and elasticity of the on-airway sampling line are much stronger than any other conventional connection tubes.