P123 Accuracy and Reliability of the Transcutaneous Carbon Dioxide (TcCO2) Signal in the Sleep Laboratory

Carbon Dioxide (CO2) monitoring is an essential part of assessing and treating disorders of hypoventilation in the sleep laboratory. While reliablity issues have been previously reported with the Transcutaneous Carbon Dioxide (TcCO2) signal, there is limited data assessing the validity of this signal or its trend in the sleep laboratory context. Therefore, this study aimed to investigate the change in TcCO2 accuracy from the beginning to the end of the sleep study in real world conditions across two different Victorian public hospital sleep laboratories that used two different TcCO2 monitors. The sample included 13 consecutive patients from Monash Health and 44 consecutive patients from Alfred Health with an average age of 64 and 56 years respectively. Arterial Blood Gas (ABG) measurements were taken prior to and following each sleep study and compared concurrently with the TcCO2 value. Bland-Altman analysis revealed an average difference between TcCO2 and PaCO2 of 3.29mmHg with agreement between -11.44 and 16.64mmHg for the TCM4 device and 1.31mmHg with agreement between -7.64 and 9.05mmHg for the TCM5 device. When accuracy was compared across time points for each patient, 46% of patients had an overnight accuracy change of ≥ 8mmHg when using the TCM4 compared with 20% when using the TCM5. It was concluded that the TcCO2 signal was un-reliable across the different monitors and that the TcCO2 trend may be difficult to interpret with confidence without blood gas calibration at the commencement and conclusion of the sleep study.

Assessing Agreement of Transcutaneous Carbon Dioxide Monitoring and Blood Gas Analysis in a Neonatal Population

Objective: To assess agreement between transcutaneous carbon dioxide (TcCO2) monitoring and blood gas analysis in neonates. Study Design: This was a prospective observational study performed in a tertiary neonatal intensive care unit. 19 infants with a mean postmenstrual age of 35+3 weeks were included. Agreement was assessed by Bland-Altman analysis and concordance correlation coefficient. End-user feedback was collected from staff and infants were assessed for evidence of skin damage. Results: Overall bias from 698 paired samples was -0.30 (SD 1.21, p<0.0001) with good concordance (CCC 0.80). 69% (95% CI 65%-72%, p=0.0003) of samples fell within the predefined clinically acceptable difference of 1kPa. Agreement was more favorable for non-invasively ventilated infants (bias -0.11, CCC 0.91). Staff feedback was positive, and no infants suffered skin damage. Conclusion: TcCO2 monitoring is a reliable assessment tool for both invasively and non-invasively ventilated neonates. It can be used as an adjunct to blood gas analysis, reducing the frequency of invasive blood tests.

Validation of transcutaneous carbon dioxide monitoring using an artificial lung during adult pulsatile cardiopulmonary bypass

Measurements of transcutaneous carbon dioxide (tcCO2) have been used in multiple venues, such as during procedures utilizing jet ventilation, hyperbaric oxygen therapy, as well as both the adult and neo-natal ICUs. However, tcCO2 measurements have not been validated under conditions which utilize an artificial lung, such cardiopulmonary bypass (CPB). The purpose of this study was to (1) validate the use of tcCO2 using an artificial lung during CPB and (2) identify a location for the sensor that would optimize estimation of PaCO2 when compared to the gold standard of blood gas analysis. tcCO2 measurements ( N = 185) were collected every 30 min during 54 pulsatile CPB procedures. The agreement/differences between the tcCO2 and the PaCO2 were compared by three sensor locations. Compared to the earlobe or the forehead, the submandibular PtcCO2 values agreed best with the PaCO2 and with a median difference of –.03 mmHg (IQR = 5.4, p < 0.001). The small median difference and acceptable IQR support the validity of the tcCO2 measurement. The multiple linear regression model for predicting the agreement between the submandibular tcCO2 and PaCO2 included the SvO2, the oxygenator gas to blood flow ratio, and the native perfusion index ( R2 = 0.699, df = 1, 60; F = 19.1, p < 0.001). Our experience in utilizing tcCO2 during CPB has demonstrated accuracy in estimating PaCO2 when compared to the gold standard arterial blood gas analysis, even during CO2 flooding of the surgical field.