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 O-2 (TcPO2) with a Radiometer TINA TCM3(R) capnograph, and a probe T degrees set at 43 degrees C. Results: Correlation between PaCO2 and TcPCO2 was high (r(2) = 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 (C) 2005 S. Karger AG, Basel.