Transcutaneous PCO2(PTCCO2) and end-tidal PCO2(PETCO2) measurement methods serve as alternatives to arterial PCO2(PaCO2), providing continuous non-invasive monitoring. The objective of this study was to evaluate the P(TC)CO(2)and P(ET)CO(2)methods with actual PaCO(2)levels, and to assess the variability of measurements in relation to subject-related factors, such as skin and subcutaneous adipose tissue thickness and presence of pulmonary diseases. PTCCO2, P(ET)CO(2)and PaCO(2)were measured at the same time in intubated pediatric subjects. Subjects' demographic characteristics, clinical features, laboratory parameters, skin and subcutaneous adipose tissue thickness were identified. The study was carried out on 102 subjects with a total of 1118 values for each method. In patients with non-pulmonary disease, the mean difference between P(TC)CO(2)and PaCO(2)was - 0.29 mmHg (+/- 6.05), while it was 0.44 mmHg (+/- 6.83) bias between P(ET)CO(2)and PaCO2. In those with pulmonary diseases, the mean difference between P(TC)CO(2)and PaCO(2)was - 1.27 mmHg (+/- 8.32), while it was - 4.65 mmHg (+/- 9.01) between P(ET)CO(2)and PaCO2. Multiple linear regression demonstrated that increased subcutaneous adipose tissue thickness, core body temperature and inotropic index were related with higher P(TC)CO(2)values relative to the actual PCO(2)values. Other factors, such as skin tissue thickness, presence of pulmonary disease, measurement location and measurement times were non-significant. The P(TC)CO(2)method has higher reliability than the P(ET)CO(2)method, and P(TC)CO(2)measurements are not influenced by most subject-related factors; however, core body temperature, inotropic index and subcutaneous adipose tissue thickness can lead to significant differences in PCO(2)measurement.