[The comparison of the value of end-tidal partial pressure of carbon dioxide after eupnoea and prolonged expiratory method in Department of Respiratory Medicine].

OBJECTIVE: To compare and discuss the value of end-tidal partial pressure of carbon dioxide (PETCO2) using eupnoea or prolonged expiratory method, and explore their application value in department of respiratory medicine.

METHODS: One hundred and fourteen patients admitted to the Department of Respiratory Medicine of hospital received PETCO2 monitor, using either eupnoea or prolonged expiratory method, and blood gas analysis was performed thereafter. Then the patients were divided into different groups according to different arterial partial pressure of carbon dioxide (PaCO2) and diseases. PETCO2 using two methods were compared and performed correlation analysis with PaCO2 was performed. A group of 45 healthy volunteers were served as the control group.

RESULTS: (1) In healthy volunteers, PETCO2 using eupnoea or prolonged expiratory method was (39.68±5.07) mm Hg (1 mm Hg=0.133 kPa), (40.68±3.25) mm Hg, respectively, and they showed a good correlation with PaCO2 [(40.44±2.70) mm Hg, r1=0.79, P1=0.02; r2=0.91, P2=0.04). (2) In 114 patients group, PETCO2 using eupnoea and prolonged expiratory method was (35.93±8.19) mm Hg, (40.69±10.71) mm Hg, respectively, and they showed a good correlation with PaCO2 [(42.90±12.62) mm Hg, r1=0.80, r2=0.86, both P<0.01). (3) Subgroup analysis according to different levels of PaCO2: in normal PaCO2 group (35-45 mm Hg, n=49), PETCO2 using eupnoea or prolonged expiratory method was (37.64±4.67) mm Hg, (38.25±5.03) mm Hg, respectively, and they showed a good correlation with PaCO2 [(39.30±3.10) mm Hg, r1=0.76, P1=0.61; r2=0.82, P2=0.65]; in low PaCO2 group (<35 mm Hg, n=26), PETCO2 by using eupnoea or prolonged expiratory method was (28.4±5.63) mm Hg, (31.3±5.47) mm Hg, respectively, and they showed a good correlation with PaCO2 [(31.27±5.47) mm Hg, r1=0.68, r2=0.87, both P<0.01]; in high PaCO2 group (45-60 mm Hg, n=27), PETCO2 by using eupnoea expiratory method [(37.07±5.04) mm Hg] showed a poor correlation with PaCO2 [(49.51±5.18) mm Hg, r=0.42, P=0.02), while PETCO2 using prolonged expiratory method [(46.61±3.75) mm Hg] showed a good correlation with PaCO2 [(49.51±5.18) mm Hg, r=0.81, P=0.01). In extremely high PaCO2 group (>60 mm Hg, n=12), PETCO2 using eupnoea or prolonged expiratory method [(51.37±11.25) mm Hg, (62.57±16.24) mm Hg] showed a good correlation with PaCO2 [(74.63±12.20) mm Hg, r1=0.80, P1=0.09; r2=0.82, P2=0.11]. (4) Subgroup analysis according to different diseases: in chronic obstructive pulmonary disease (COPD) group (n=31), large pleural effusion group (n=21), and interstitial pneumonia group (n=15), PETCO2 using eupnoea expiratory method [(44.62±12.70), (34.89±3.26), (34.82±4.51) mm Hg] showed a poor correlation with PaCO2 [(60.18±17.38), (38.02±3.66), (38.70±4.08) mm Hg, r1=0.87, P1<0.01; r2=0.23, P2=0.03; r3=0.56, P3=0.02], while PETCO2 using prolonged expiratory method [(55.63±16.27), (38.59±4.23), (37.81±4.23) mm Hg] showed a good correlation with PaCO2 [(60.18±17.38), (38.02±3.66), (38.70±4.08) mm Hg, r1=0.89, P1<0.01; r2=0.66, P2=0.02; r3=0.87, P3=0.01]. In pulmonary embolism group (n=16), the results of PETCO2 using eupnoea and prolonged expiratory method [(30.57±9.49) mm Hg, (32.90±8.57) mm Hg] showed a good correlation with PaCO2 [(36.50±4.59) mm Hg, r1=0.75, r2=0.76, both P<0.01].

CONCLUSIONS: In Department of Respiratory Medicine, PETCO2 can replace PaCO2, but among the patients with COPD, interstitial pneumonia, large pleural effusion, the results of PETCO2 measured with prolonged expiratory method could be closer to that of PaCO2 as compared with that of using eupnoea expiratory method. In cases with high levels of PaCO2, blood gas analysis should be executed. In pulmonary embolism patients, there was no difference between eupnoea and prolonged expiratory method, and the results were lower than that of PaCO2.