Non-invasive (transcutaneous) monitoring of PCO2 (TcPCO2) in older adults

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.

To analyse the agreement between transcutaneous and arterial measurement of PaO2 and PaCO2 in older adults.

Prospective descriptive study performed in the intermediate-care unit of a geriatric university hospital and a pulmonary rehabilitation centre.

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 degrees set at 43 degrees C.

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.

In older subjects, TcPCO2 (but not TcPO2) measurements are reliable when repeated assessment of ABG is warranted.