Prolonged expiratory method and curve fitting method used in exploratory study of expiratory capnography in elderly patients with chronic obstructive pulmonary disease / 中华老年医学杂志

ABSTRACT

Objective To find noninvasive estimation of partial pressure of carbon dioxide in artery (PaCO2) by measuring the end-tidal CO2 partial pressure (PETCO2) in elderly patients with respiratory failure with chronic obstructive pulmonary disease (COPD). Methods All the 30 acutely exacerbated COPD subjects received routine clinical treatment including bronchodilators,mucolytics, glucocorticosteroid, antibiotics and oxygen therapy for 5-7 days, and part of them received noninvasive positive-pressure ventilation (NIPPV) treatment concurrently. They were both tested by eupnea method and prolonged expiratory method before and after treatment. Results Before treatment, PET CO2 (Q) (end-tidal CO2 pressure with eupnea, (50.72±8.93) mm Hg wassignificantly lower than PaCO2 (F=38.73, P＜0.01 ). Yet, PETCO2(P) (end-tidal CO2 pressure with prolong expiration) was (70.35±8.91) mm Hg and PaCO2 was (71.25±9.08) mm Hg. There was no significant difference between PETCO2 (P) and PaCO2 (P＞0.05). The similar results were found after treatment. By linear regression analysis, PetCO2(P) was remarkably positive correlated with PaCO2 before and after treatment (r=0.96 and 0.97, respectively, P＜0.01). According to TABG,PCO2(C) which was calculated by the average expiratory time of fitting curve was (71.78±9.04)mm Hg. And there was no significant difference between PCO2 (C) and PaCO2 (P＞0.05);Thesimilar results were founcl after treatment. By linear regression analysis, PCO2 (C) was remarkably positively correlated with PaCO2 (r=0.97 and 0.98, respectively, P＜0.01) before and after treatment. Conclusions In COPD patients with type Ⅱ respiratory failure, conventional PETCO2 (Q) is significantly lower than PaCO2. Yet, PETCO2 (P) could exactly estimate PaCO2 and is appropriate to its dynamic monitoring. And PCO2 (C) which is calculated by mode Boltzmann on eupnea curve also obtain similar results.