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Introduction Transcutaneous Carbon Dioxide monitors (tcpCO2) are used to assess nocturnal gas exchange efficiency in children with various sleep breathing disorders. The American Academy of Sleep Medicine (AASM) 2023 manual defines nocturnal hypoventilation in children when > 25% of the total sleep time is spent with pCO2 > 50 mmHg (6.7 kPa). Studies have shown discrepancies between tcCO2 and arterial pCO2, as well as technical challenges obtaining tcCO2 data overnight. We compared the performance of two different tcCO2 monitors in children in terms of quantity and quality of data collected and if the position of the sensor probe had any impact.Methods This was a prospective analysis of 57 children undergoing consecutive hospital-based cardio-respiratory polygraphy over a two-month period in our nurse led sleep lab. Patients attending hospital for cardiorespiratory sleep studies on PAP therapy were excluded from the audit.Results 29 patients underwent studies on TCM5 (Radiometer, UK) and 28 patients on Sentec TCM (Sentec, UK) over a period of two months. Data was analysed using Visi-Download (Stowood Scientific Instruments). Statistical significance between the data acquired across both monitors was calculated using paired t-tests. Mean age, sex, height, weight and AHI were not statistically different between both groups. CO2 mean was significantly different between Sentec and TCM5 (5.15 kPa vs 6.02 kPa), as was CO2 max (5.75 kPa vs 7.06 kPa). Four patients met hypoventilation criteria using TCM5 and only one using Sentec. Mean tcCO2 was higher in patients using TCM5, however time > 6.7 kPa was not significantly different between groups. There were 27 studies in the TCM5 group vs 19 studies in the Sentec group with recording > 6 hrs, however% artefact removed between both groups was not significant. Artefact was irrespective of site location on TCM5, however using Sentec was more common with the forehead. ( Table 1)Abstract P48 Table 1Summary demographic data and comparison of the quality/quantity of tcCO2 data acquired from groups. Data expressed as mean (M) and standard deviation (SD). NS = non-significant P value, * significant P value < 0.05, ** significant P value < 0.001Conclusions There appeared to be no significant difference in% artefact excluded from analysis time between either monitor. TCM5 group showed more studies recorded > 6 hrs and artefact was regardless of sensor probe position. Forehead site was used in younger patients and Sentec appeared to perform less well compared to other probe sites in terms of artefact.