Evaluation of correlation between end tidal carbondoxide levels and artery blood gas that diagnosed hyperventilation syndrome in patients with dyspnea in emergency room

Background and Aims: End-Tidal CO2 (ETCO2) measurement is a widely used non-invasive method in the emergency department and anesthesia service, which is proven reliable and supported by metaanalysis. In many diseases and healthy humans, ETCO2 and CO2 measured in arterial blood gas are correlated. In this study, we aimed to compare arterial blood gas sampling and blood partial carbon dioxide levels measured by capnography in patients with hyperventilation syndrome who were admitted with dyspnea and to demonstrate that a non-invasive procedure can be used to improve patient comfort. Materials and Methods: This prospective, observational study included patients who presented with dyspnea for a period of one year between 2018 – 2019 and were thought to have hyperventilation syndrome. ETCO2 measured from patients via an airway adapter attached to the capnometer. Arterial blood gas samples were obtained at the same time. Results: The study included 44 patients (female: 30 / %68.2). The results were found as mean blood gas PCO2 (female: 29.9 (10.7 - 46.3), male: 30.1 (18.1 - 39.3)) and mean ETCO2 (female: 28.1(16.0 - 45), male: 29.0 (15.0 - 38)) values of the patients, PCO2-ETCO2 difference (female: 1.82 (-17.4 - 18.5), male: 1.1 (-7.50 – 13.7)) and its mean values (female: 28.1 (16 - 45), male: 29.0 (15.0 – 38.0)). There was a moderate correlation (r: 0.531) between end-tidal and blood gas measurements totally, and a moderate correlation in women (pearson r: 0.49) and stronge correlation in men (pearson r: 0.65). The limits found in the Bland-Altman analysis were not clinically acceptable. Conclusion: In many studies, there was a correlation between CO2 levels measured by blood gas sampling method and ETCO2 levels. In some studies, ETCO2 measurement was used alone and reliable results were obtained. However, our study was performed in hyperventilation syndrome patients specifically and there was no clinically acceptable agreement between arterial blood gas method and ETCO2 method. Therefore, it was seen that ETCO2 measurement could not be used instead of blood gas sampling in patients with hypocapnia syndrome. Keywords: Hyperventilation, Hypocapnia, PCO2, Capnometer, ETCO2