The transcutaneous measurement of oxygen (tcPO2) and carbon dioxide (tcPCO2) tensions may serve as a surrogate of arterial oxygen (PaO2) and carbon dioxide (PaCO2) tensions, respectively. We investigated the effects of the electrode temperature of a new device, TCM4, on the measurement of tcPO2 and tcPCO2. Twenty-five patients scheduled for major lower abdominal surgery were enrolled. The electrode of the TCM4 was attached to the chest, with its temperature set to 37°C, 40°C, 42°C, 43°C, or 44°C. tcPO2, tcPCO2, end-tidal carbon dioxide tension (EtCO2), PaO2, and PaCO2 were simultaneously measured at various EtCO2 levels and inhaled oxygen concentrations. The times required for stabilization of the tcPO2 and tcPCO2 values were measured. A Bland-Altman plot was used to compare the two measurements. The time required for stabilization was shorter with a higher electrode temperature, but the shortest time was still more than 150 s. TcPO2 correlated well with PaO2 at 43°C and 44°C. TcPCO2 correlated well with PaCO2 and EtCO2 at 43°C. The bias and limits of agreement were larger with lower electrode temperature for TcPO2—PaO2, tcPCO2—PaCO2, and tcPCO2—EtCO2. We concluded that the electrode of the TCM4 should be heated to at least 43°C to measure tcPO2 and tcPCO2. However, the absolute values of tcPO2 and tcPCO2 could not be used as surrogate measurements of PaO2 and PaCO2, respectively.
Transcutaneous oxygen tensionTranscutaneous carbon dioxide tensionElectrode temperature