Evaluation of a transcutaneous carbon dioxide monitor (“TOSCA”) in adult patients in routine respiratory practice

SummaryBackgroundNon-invasive measurement of oxygenation is routine in adult clinical practice but transcutaneous monitoring of PCO2 (PtcCO2) is used much less due to technical difficulties with earlier transcutaneous electrodes.ObjectiveOur aim was to determine the reliability of estimating arterial PCO2 (PaCO2) using a recently introduced combined SaO2/PtcCO2 monitor (“TOSCA”, Linde Medical Systems) in adult patients in routine clinical respiratory practice.MethodsPtcCO2 was measured in patients requiring arterial blood gases for clinical reasons. Ten minutes after the probe had been attached to an earlobe PtcCO2 was recorded, immediately before arterial blood sampling. The PCO2 values obtained were compared by Bland–Altman analysis.ResultsSamples were taken from 48 unselected patients with varied pathology. There were no technical problems. Median age was 56 years (range 20–86 years). The mean difference between PaCO2 and PtcCO2 was −0.04 kPa, sd of the difference 0.67 kPa. Bland–Altman analysis showed generally good agreement between the two measurements across the range of PaCO2 values (4–10.9 kPa). Four of 48 measurements showed a PCO2 difference >1 kPa with no technical or clinical explanations apparent.ConclusionsThe accuracy of estimation of PaCO2 by the TOSCA transcutaneous electrode was generally good and the device appears promising for use in routine clinical respiratory practice.