The Copmparison of Accuracy of PtcCO2 and in PetCO2 in COPD Patients With NIV Treatment

The chronic obstructive pulmonary disease (COPD) patients with type II respiratory failure always needs PaCO2 test to monitor the changes of disease. Method used mostly nowadays to detect PaCO2 is arterial puncture which is accurate but is invasive, painful and non-dynamic. Noninvasive measurement methods includes end-tidal CO2 (PetCO2), transcutaneous CO2 (PtcCO2) which can monitor the PaCO2 dynamically and noninvasively, but their accuracy is in controversy. Common PetCO2 is especially inaccurate in COPD patients while our team find that the accuracy can be improved by prolong expiration method (PetCO2 (P)).So the investigators want to compare the accuracy of PtcCO2 and PetCO2(P) in AECOPD patients during noninvasive ventilation(NIV).