Accuracy of a transcutaneous carbon dioxide monitor during the 6-minute walk test in COPD patients - a pilot study

Background: Chronic respiratory failure can be associated with CO 2 retention and hypercapnia during exercise in COPD patients. A continuously monitoring of transcutaneous CO 2 levels (T c PCO 2 ) may be useful to screen CO 2 trends and to identify patients with exercise-induced hypercapnia (EIH). Objective: The aim of this study was to investigate the accuracy of the SenTec Digital Monitoring System (SDMS, SenTec AG, Therwil, Switzerland) during the 6-minute walk test (6MWT) in COPD patients. Methods: 10 COPD patients were enrolled in this prospective, pilot study. Capillary blood gases (CBG) from the earlobe were taken by the same investigator pre-6MWT and directly following 6MWT withT c PCO 2 levels recorded simultaneously. To ensure a valid comparison between CBG and T c PCO 2, values were taken at the same time point. An independent person set digital markers in the SenTec device concurrently with the taking of the CBG. Results: The agreement of PCO 2 recording between CBG and SenTec device showed a very strong intra-class correlation coefficient for pre-walk (ICC=0.98, 95%CI: 0.93-0.99) and post-walk (ICC=0.98, 95CI: 0.73-0.99) values of the 6MWT (see Figure). Conclusion: Transcutaneously measured PCO 2 values by the SDMS during 6MWT were highly accurate. The strong correlation with CBG and the continuous, non-invasive method could be advantageous to detect patients with EIH during the 6MWT.