Correlation and agreement of Transcutaneous capnography carbon dioxide (TcCO2) with arterial carbon dioxide pressure (PaCO2) have been studied before, mostly in neuromuscular, COPD or acute respiratory failure patients.

Aims and objectives

Our objective was to determine the correlation and agreement of nocturnal TcCO2 with gold standard in a real-world scenario.


Observational and prospective study of consecutive patients in stable and acute condition, from June of 2019 to November of 2023. A 7-hour record of TcCO2 was performed, with a temperature of 42ºC. Correlation was assessed by the Spearman statistics, while agreement by Intraclass correlation coefficients (ICC) in two factors, random events model. Furthermore, Bland-Altman plot analysis was also obtained, and regression linear analysis for ruling out proportional bias.  


Seventy-three patients were included, with a mean age of 62.3 ± 18.3 years, 44 were males (60.4%).  Mean TcCO2 was 45.9 ± 10.7 mmHg and mean PaCO2 47.6 ± 11.5 mmHg. Correlation of TcCO2 and PaCO2 was of 0,90 (CI95% 0.81 ? 0.95, p<0.001) and ICC of 0.92 (CI95% 0.86 - 0.95, p<0.05). Bland-Altman plot demonstrated a mean difference of 1,69 mmHg (limits of agreement -6,5 ? 9,9). Table 1 presents correlations and ICC according to aetiology of respiratory failure. As well, Graphic 1 shows Bland Altman plots according to respiratory failure aetiology.


Transcutaneous capnography presented an acceptable reliability when compared to arterial carbon dioxide. However, the agreement differed among the aetiology of respiratory failure: obesity hypoventilation syndrome presented the highest and the acute scenario the lowest.