Abstract

Objectives: Patients arriving in the emergency department (ED) need rapid and reliable evaluation of their respiratory status. Mainstream end tidal carbon dioxide (ETCO₂) is one of the methods used for this purpose during general anaesthesia of intubated patients in the operating theatre. Sidestream ETCO₂ (SSETCO₂) might be a non-invasive, rapid, and reliable predictor of arterial Pco₂ in non-intubated patients in respiratory distress. The aim of this study was to verify whether SSETCO₂ can accurately predict the arterial Pco₂ and to detect variables that may affect this correlation.

Methods: A prospective semi-blind study. The participants were 73 patients (47 men, 26 women) referred to the ED for respiratory distress. Arterial blood gas pressures and SSETCO₂ measurements were performed and recorded for all patients. Other parameters recorded were: age; body temperature; respiratory rate; blood pressure; pulse rate; and medical diagnosis.

Results: A significant correlation was found between SSETCO₂ and arterial Pco₂ (r = 0.792). Compared with the correlation curve of the whole group, age under 50 years deflected the correlation curve to the left, while temperature above 37.6°C deflected it to the right. The rest of the parameters had no clear influence on the SSETCO₂/Pco₂ correlation curve.

Conclusions: There is a good correlation between SSETCO₂ and arterial Pco₂ in the ED setting. Young age may increase the arterial Pco₂/SSETCO₂ gradient while raised temperature may decrease this gradient. Further studies are needed to confirm these findings in the normal healthy population.