Validation of a transcutaneous CO(2) monitor in adult patients with chronic respiratory failure.

BACKGROUND

Home mechanical ventilation is usually started in hospital as arterial blood gas sampling is deemed necessary to monitor CO(2) and O(2) adequately during institution of ventilatory support. A non-invasive device to reliably measure CO(2) transcutaneously would alleviate the need for high care settings for measurement and open the possibility for home registration.

OBJECTIVES

In this study we investigated whether the TOSCA® transcutaneous CO(2) (PtcCO(2)) measurements, performed continuously during the night, reliably reflect arterial CO(2) (PaCO(2)) measurements in adults with chronic respiratory failure.

METHODS

Paired measurements were taken in 15 patients hospitalised to evaluate their blood gas exchange. Outcomes were compared 30 min, 2, 4, 6 and 8 h after attaching the sensor to the earlobe. A maximum difference of 1.0 kPa and 95% limits of agreement (LOA) of 1 kPa between CO(2) pressure measurements, following the analysis by Bland and Altman, were determined as acceptable.

RESULTS

Mean PtcCO(2) was 0.4 kPa higher (LOA -0.48 to 1.27 kPa) than mean PaCO(2) after 30 min. These figures were 0.6 kPa higher (LOA -0.60 to 1.80 kPa) after 4 h, with a maximum of 0.72 kPa (LOA 0.35 to 1.79 kPa) after 8 h. The corresponding values for changes in PtcCO(2) versus PaCO(2) were not significant (ANOVA).

CONCLUSIONS

PtcCO(2) measurement, using TOSCA, is a valid method showing an acceptable agreement with PaCO(2) during 8 h of continuous measurement. Therefore, this device can be used to monitor CO(2) adequately during chronic ventilatory support.