Background and Goal of Study: The purpose of this study is to determine the accuracy of end-tidal carbon dioxide (PETCO2) obtained at nose through the smart capnoline O2TM and at pharynx through the smart capnoline H with supplemental oxygen by five liters per minute in nonintubated patients undergoing digital subtraction cerebral angiography (DSA).
Materials and Methods: This is a prospective, observational study. Twenty unconscious patients undergoing DSA were included. PETCO2 was measured at nose sampled via the smart capnoline O2TM and at pharynx via the smart capnoline H which was placed at pharynx through nasopharynx airway. Oxygen was administered through smart capnoline O2TM at a rate of five liters per minute.
After PETCO2 stable for five minutes, arterial blood sample was drawn from an indwelling femoral catheter for analyzing arterial carbon dioxide partial pressure (PaCO2) and PETCO2 measured via nose and pharynx were simutaneously recorded. When DSA procedure was over, PaCO2 was analyzed again. Data were analyzed by Pearson correlation and Bland-Altman analysis.
Results and Discussion: Both PETCO2 sampled from the nose and the pharynx were highly correlated with PaCO2, and the correlation coefficients were approximate values, 0.832 (p< 0.0001) for PaCO2 with PETCO2 via nose and 0.836 (p< 0.0001) for PaCO2 with PETCO2 via pharynx. The mean bias ± SD between PETCO2 and PaCO2 was 4.53±2.76 mmHg (nose) and 3.22±2.86 mmHg (pharynx). The 95% limits of agreement between PETCO2 and PaCO2 ranged from -0.90 mmHg to 9.95 mmHg (nose), and ranged from -2.39 mmHg to 8.82 mmHg (pharynx). End tidal CO2 measurements via nose and pharynx had comparable performance. The correlation between PETCO2 measured via nose and pharynx was 0.971(p< 0.001). The difference between PETCO2 measured via nose and pharynx was 1.31 ± 1.25 mmHg.
Conclusion(s): This study demonstrated that a high correlation and good agreement between PETCO2 measured via nose and pharynx and PaCO2 was obtained. Therefore, PETCO2 derived from nose and pharynx was accurate and reliable in nonintubated patients during DSA.