Speed of response and accuracy of two transcutaneous carbon dioxide monitors

Two instruments (Radiometer and Hewlett-Packard) for measuring transcutaneous carbon dioxide levels have been compared. Their warm-up times, speed of response and accuracy in predicting arterial PCO2have been assessed in six normal subjects and ten patients with respiratory problems. They both performed well with similar accuracy in predicting PaCO2[95% confidence limits ± 0.9 kPa (6.7 mmHg)]. The warm-up time following application depended on actual PaCO2but was approximately 10 min for normal subjects and 15 min in patients. Their response to step changes in PaCO2was complete in approximately 6 min. Prior skin abrasion (essential for the Hewlett-Packard) increased the speed of response of the Radiometer considerably and this is the faster instrument. The Hewlett-Packard proved easier to use. These instruments are a significant advance in non-invasive monitoring.