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

Abstract

Background: Non-invasive measurement of oxygenation is routine in adult clinical practice but transcutaneous monitoring of PCO(2) (PtcCO(2)) is used much less due to technical difficulties with earlier transcutaneous electrodes.

Objective: Our aim was to determine the reliability of estimating arterial PCO(2) (PaCO(2)) using a recently introduced combined SaO(2)/PtcCO(2) monitor ("TOSCA", Linde Medical Systems) in adult patients in routine clinical respiratory practice.

Methods: PtcCO(2) was measured in patients requiring arterial blood gases for clinical reasons. Ten minutes after the probe had been attached to an earlobe PtcCO(2) was recorded, immediately before arterial blood sampling. The PCO(2) values obtained were compared by Bland-Altman analysis.

Results: Samples 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 PaCO(2) and PtcCO(2) was -0.04kPa, sd of the difference 0.67kPa. Bland-Altman analysis showed generally good agreement between the two measurements across the range of PaCO(2) values (4-10.9kPa). Four of 48 measurements showed a PCO(2) difference >1kPa with no technical or clinical explanations apparent.

Conclusions: The accuracy of estimation of PaCO(2) by the TOSCA transcutaneous electrode was generally good and the device appears promising for use in routine clinical respiratory practice.