Evaluation of the Relationship between Transcutaneous Carbondioxide Monitorization and End-tidal Carbondioxide and Partial Carbondioxide Monitorization

MonitorizationNon-invasive methods have replaced invasive methods in line with developments in pediatric intensive care units. (Especially methods that enable continuous monitoring) Although arterial carbon dioxide measurement is still the gold standard for the evaluation of alveolar ventilation, the need for continuous monitoring of PaCO2 and the invasive nature of this method have led to the investigation of alternative methods. To evaluate the correlation of transcutaneous CO2 (TcCO2) monitoring with PaCO2 and ETCO2 in mechanically ventilated patients in peditaric intensive care units. Single-center, prospective, observational cohort study. We enrolled 60 patients between the age of 1 month-18 years who were mechanically ventilated in pediatric intensive care unit for this single-center, prospective, observational cohort study from February 2019 through March 2019. Correlation analysis was performed for arterial PaCO2, end-tidal CO2, TcCO2 parameters. P<0.05 values were considered significant. The Bland-Altman plot was created for determining the agreement between the methods. The correlation of transcutaneous CO2 and end-tidal CO2 with arterial PaCO2 was evaluated, both parameters were found to be positively and highly correlated (r=0.864, p<0.001, r:0.962, p<0.001, respectively). The mean bias between the arterial carbondioxide mesaurement and transcutaneous measurement was 5.5, and limits of agreement (bias ±1.96 SD) ranged from -13.9 to 2.9. The mean bias between the arterial carbondioxide mesaurement and end-tidal carbondioxide measurement was 2.3, and limits of agreement (bias ±1.96 SD) ranged from -4.1 to 8.6. In 44 measurements (88%), the TcCO2 was ±7.5 mm Hg of the PaCO2. TcCO2 seems to be a good alternative for carbon dioxide measurement, as it is non-invasive and allows continuous monitoring in view of today's intensive care conditions, but arterial PaCO2 measurement is still the gold standard method. Continuous TcCO2 monitoring provides a promising alternative to repeated blood sampling in subjects requiring mechanical ventilation for critically ill children.

Effect of High Atmospheric Carbon Dioxide Concentrations on the Serum Total Carbon Dioxide Measurement

Background: Serum total carbon dioxide (TCO₂) measurements are easily affected by numerous factors. Whether an irregularly high atmospheric CO₂ concentration affects the TCO₂ measurement remains unclear. Materials and Methods: In Somdech Phra Debaratana Medical Center laboratory (SDMC) and the main building laboratory (Building 1) located within Ramathibodi Hospital, Mahidol University, Bangkok, Thailand, the repeated TCO₂ measurements using an enzymatic assay in three levels of human based control material were performed every two hours, over a one-day period. TCO₂ in a total of 150 patient sera were measured. Simultaneously, atmospheric CO₂ levels were determined. Results: Atmospheric CO₂ levels in SDMC and Building 1, ranged from 763 to 1,560 ppm and 602 to 787 ppm, respectively. Repeated TCO₂ measurements for SDMC, the measured TCO₂ concentrations of all control materials clearly increased between 10:00 a.m. and 4:00 p.m., with the peak at 2:00 p.m., which was related to an increase in the atmospheric CO₂ concentration. By contrast, in Building 1, the measurements were considerably stable. Moreover, considering patient data (n=12,042), the estimate median TCO₂ concentration in SDMC was likely to increase between 10:00 a.m. to 4:00 p.m. as well. The association between the bias (y), difference TCO₂ concentration obtained between the SDMC and the Building 1, and the increasing atmospheric CO₂ (x) was y = 0.0038x – 0.016, R²=0.6813. Using regression equations, TCO₂ level increased by approximately 0.4 mmol/L for every 100 ppm of CO₂ increase in atmosphere. Conclusion: High atmospheric CO₂ concentrations can result in falsely high TCO₂ values, which may lead to markedly wrong interpretations, especially in patients with a tendency to have low TCO₂ concentrations. Keywords: Serum total carbon dioxide, Atmospheric carbon dioxide, Acid-base disorder

Toward high precision XCO2 retrievals from TanSat observations

&lt;p&gt;TanSat is the 1&lt;sup&gt;st&lt;/sup&gt; Chinese carbon dioxide measurement satellite, launched in 2016. Preliminary TanSat XCO&lt;sub&gt;2&lt;/sub&gt; retrievals have been introduced in previous studies based on the 1.6 m weak CO&lt;sub&gt;2&lt;/sub&gt; band. In this study, the University of Leicester Full Physics (UoL-FP) algorithm is implemented for TanSat nadir mode XCO&lt;sub&gt;2&lt;/sub&gt; retrievals. We develop a spectrum correction method to reduce the retrieval errors by an online fitting of an 8&lt;sup&gt;th&lt;/sup&gt; order Fourier series. The model and a priori is developed by analyzing the solar calibration measurement. This correction provides a significant improvement to the O&lt;sub&gt;2&lt;/sub&gt; A band retrieval. Accordingly, we extend the previous TanSat single CO&lt;sub&gt;2&lt;/sub&gt; weak band retrieval to a combined O&lt;sub&gt;2&lt;/sub&gt; A and CO&lt;sub&gt;2&lt;/sub&gt; weak band retrieval. A Genetic Algorithm (GA) has been applied to determine the threshold values of post-screening filters. In total, 18.3% of the retrieved data is identified as high quality compared. The same quality control parameters have been used in the bias correction due to the stronger correlation with the XCO&lt;sub&gt;2&lt;/sub&gt; retrieval error. A footprint independent multiple linear regression is applied to determine the sounding XCO&lt;sub&gt;2&lt;/sub&gt; retrieval error and bias correction. Twenty sites of the Total Column Carbon Observing Network (TCCON) have been selected to validate our new approach of the TanSat XCO&lt;sub&gt;2&lt;/sub&gt; retrieval. We show that our new approach produces a significant improvement of the XCO&lt;sub&gt;2&lt;/sub&gt; retrieval accuracy and precision when compared with TCCON with an average bias and RMSE of -0.08 and 1.47 ppm respectively. The methods used in this study, such as continuum correction, can help to improve the XCO&lt;sub&gt;2&lt;/sub&gt; retrieval from TanSat and subsequently the Level-2 data production, and hence will be applied in the TanSat operational XCO&lt;sub&gt;2&lt;/sub&gt; processing.&lt;/p&gt;