Clinical usefulness of end-tidal CO₂ measured using a portable capnometer in patients with respiratory disease

Introduction: This study aimed to evaluate the correlation and agreement between end-tidal CO₂ (EtCO₂) measured with the novel portable capnometer (CapnoEye®) and partial pressure of arterial carbon dioxide (PaCO₂) levels in patients with respiratory diseases and to compare the efficacy of EtCO₂ and PvCO₂ in predicting PaCO₂ levels. Methods: We analyzed the correlation and the agreement between EtCO₂ and PaCO₂ and between PvCO₂ and PaCO₂ using Pearson's moment correlation coefficient in patients with type 1 and type 2 respiratory failure and both groups overall. Results: A total of 100 samples were included that comprised 67 men (67%). The mean age of the subjects was 77 ± 13 years. Chronic obstructive pulmonary disease (COPD) (43%) was the most common disease. There was a high correlation between EtCO₂ and PaCO₂ (r = 0.88; p < 0.0001). Sixty-six PvCO₂ samples were obtained, and there was a high correlation between PvCO₂ and PaCO₂ (r = 0.81; p < 0.0001). Regarding type 2 respiratory failure, there was a high correlation between EtCO₂ and PaCO₂ (r = 0.81). The Bland–Altman analysis between PaCO₂ and EtCO₂ revealed a bias of 5.7 mmHg, with limits of agreement ranging from −5.1 mmHg to 16.5 mmHg. In contrast, the analysis between PaCO₂ and PvCO₂ revealed a bias of −6.8 mmHg, and the limits of agreement ranged from −22.13 mmHg to 8.53 mmHg. Conclusion: EtCO₂ measured by CapnoEye® was significantly correlated to PaCO₂ levels in patients with respiratory diseases. Moreover, CapnoEye® may be more useful for predicting hypercapnia conditions in which respiratory diseases are compared with measure PvCO₂.