Objectives Continuous blood gas monitoring is frequently necessary in critically ill patients. Our aim was to assess the accuracy of transcutaneous CO₂ tension (PtcCO₂) monitoring in the emergency department (ED) assessment of hypotensive patients by comparing it with the gold standard of arterial blood gas analysis (ABGA).

Methods All patients receiving PtcCO₂ monitoring in the ED were included. We excluded paediatric patients, patients with no ABGA results during a hypotensive event, patients whose ABGA was not performed simultaneously with PtcCO₂ monitoring, and patients who received sodium bicarbonate for resuscitation. The included patients were classified into hypotensive patients and normotensive patients. A hypotensive patient was defined as a patient showing a mean arterial pressure under 60 mm Hg. The agreement in measurement between PaCO₂ tension (PaCO₂) and PtcCO₂ were investigated in both groups.

Results The mean difference between PaCO₂ and PtcCO₂ was 2.1 mm Hg, and the Bland–Altman limits of agreement (bias±1.96 SD) ranged from −15.6 to 19.7 mm Hg in the 28 normotensive patients. The mean difference between PaCO₂ and PtcCO₂ was 1.1 mm Hg, and the Bland–Altman limits of agreement (bias±1.96 SD) ranged from −19.5 to 21.7 mm Hg in the 26 hypotensive patients. The weighted κ values were 0.64 in the normotensive patients and 0.60 in the hypotensive patients.

Conclusions PtcCO₂ monitoring showed wider limits of agreement with PaCO₂ in urgent situations in the ED environment. However, acutely developed hypotension does not affect the accuracy of PtcCO₂ monitoring.