For the evaluation of the correlation between the ETCO2 and the PaCO2 in post-extubated spontaneously breathing patients, we tested 30 patients in recovery room with Salter Divided Nasal Cannula, which have permanent bamer in the face piece and a dual tubing set that allows end tidal sampling from one nare and oxygen delivery to the other. When the wave form of capnogram looked regular and normal, the value of ETCO2 was recorded and the arterial blood was taken from the radial artery to analize blood gas immediately. The results were as following; 1. The mean value of PaCO2 was 42.0±4.8 mmHg. 2. The mean value of P(ET)CO2 was 39.3±5.1 mmHg. 3. The value of P(ET)CO2 acquired with Salter Divided Nasal Cannula hase close positive correlation with the values of the PaCO2. (PaCO2=0.75 x P(ET)CO2±12.64, r=0.79, p<0.001)