Validation of a Transcutaneous CO2 Monitor in Adult Patients with Chronic Respiratory Failure

Abstract

Background: Home mechanical ventilation is usually started in hospital as arterial blood gas sampling is deemed necessary to monitor CO₂ and O₂ adequately during institution of ventilatory support. A non-invasive device to reliably measure CO₂ transcutaneously would alleviate the need for high care settings for measurement and open the possibility for home registration. Objectives: In this study we investigated whether the TOSCA® transcutaneous CO₂ (PtcCO₂) measurements, performed continuously during the night, reliably reflect arterial CO₂ (PaCO₂) measurements in adults with chronic respiratory failure. Methods: Paired measurements were taken in 15 patients hospitalised to evaluate their blood gas exchange. Outcomes were compared 30 min, 2, 4, 6 and 8 h after attaching the sensor to the earlobe. A maximum difference of 1.0 kPa and 95% limits of agreement (LOA) of 1 kPa between CO₂ pressure measurements, following the analysis by Bland and Altman, were determined as acceptable. Results: Mean PtcCO₂ was 0.4 kPa higher (LOA –0.48 to 1.27 kPa) than mean PaCO₂ after 30 min. These figures were 0.6 kPa higher (LOA –0.60 to 1.80 kPa) after 4 h, with a maximum of 0.72 kPa (LOA 0.35 to 1.79 kPa) after 8 h. The corresponding values for changes in PtcCO₂ versus PaCO₂ were not significant (ANOVA). Conclusions: PtcCO₂ measurement, using TOSCA, is a valid method showing an acceptable agreement with PaCO₂ during 8 h of continuous measurement. Therefore, this device can be used to monitor CO₂ adequately during chronic ventilatory support.