Non-Invasive (Transcutaneous) Monitoring of PCO2 (TcPCO2) in Older Adults.

Background: Transcutaneous measurements of arterial blood gases (ABG) may decrease the need for repeated arterial puncture in older patients treated for acute cardiac or pulmonary disorders. However, age-related changes in skin perfusion, metabolism, or thickness may alter the validity of the technique. Objective: To analyse the agreement between transcutaneous and arterial measurement of PaO₂ and PaCO₂ in older adults. Design: Prospective descriptive study performed in the intermediate-care unit of a geriatric university hospital and a pulmonary rehabilitation centre. Methods: 40 patients, aged 82.5 ± 8 years (66–97), hemodynamically stable, without vasopressor treatment, underwent simultaneous measurement of arterial blood gases (ABG) and transcutaneous CO₂ (TcPCO₂) and O₂ (TcPO₂) with a Radiometer TINA TCM3^® capnograph, and a probe T° set at 43°C. Results: Correlation between PaCO₂ and TcPCO₂ was high (r² = 0.86) with a low bias (–0.1 mm Hg) and limits of agreement quite compatible with clinical use: (8.3; –8.5 mm Hg). The probe was well tolerated without any cutaneous lesion even after prolonged recordings (up to 8 h). Conversely, although TcPO₂ and PaO₂ were significantly correlated, the variability around the regression line precludes the use of transcutaneous measurements for monitoring PaO₂ in a clinical setting. Conclusion: In older subjects, TcPCO₂ (but not TcPO₂) measurements are reliable when repeated assessment of ABG is warranted. Copyright © 2005 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]