Evaluation of a System for Transcutaneous Long-Term Capnometry

Abstract

<i>Background:</i> The measurement of CO<sub>2</sub> partial pressure (P<i>CO</i><sub>2</sub>) is of great importance. Former systems of transcutaneous capnometry combining the measurement of oxygen partial pressure (P<i>O</i><sub>2</sub>) and P<i>CO</i><sub>2</sub> had their limitations due to skin irritations caused by the heating-up of the sensor and a short application time of 4 h. <i>Objectives:</i> To evaluate for the first time combined monitoring of transcutaneous P<i>CO</i><sub>2</sub> (tcP<i>CO</i><sub>2</sub>) and oxygen saturation applying a lower temperature (sensor temperature 42°C) and a new sensor technology in healthy individuals during sleep. <i>Methods:</i> Twenty-nine healthy individuals [12 males, age 35.2 ± 17.0 years, body height: 170.2 ± 12.0 cm (mean ± SD), weight: 76.3 ± 15.8 kg, body mass index 26.5 ± 5.4] were monitored for more than 6 h at night with the TOSCA 500 instrument (Radiometer, Basel, Switzerland). tcP<i>CO</i><sub>2</sub> was continuously monitored and its correlation with selective measured capillary P<i>CO</i><sub>2</sub> values (Pcap<i>CO</i><sub>2</sub>) was monitored at 0.00 and 4.00 h. <i>Results:</i> At 0.00 h, Pcap<i>CO</i><sub>2</sub> was 37.1 ± 5.1 mm Hg and tcP<i>CO</i><sub>2</sub> was 43.4 ± 6.6 mm Hg (p < 0.001). At 4.00 h, Pcap<i>CO</i><sub>2</sub> was 37.0 ± 5.6 mm Hg and tcP<i>CO</i><sub>2</sub> was 43.5 ± 5.4 mm Hg (p < 0.001). Pcap<i>CO</i><sub>2</sub> and tcP<i>CO</i><sub>2</sub> were positively and significantly correlated (0.00 h: r = 0.5, p < 0.02 and 4.00 h: r = 0.72 and p < 0.001) at both time points. In the course of the night, there was no significant drift in the tcP<i>CO</i><sub>2</sub> values. <i>Conclusion:</i> The investigated system enables stable measurement of tcP<i>CO</i><sub>2</sub> without relevant drift in healthy individuals and does not require recalibration. tcP<i>CO</i><sub>2</sub> is highly suitable as a measure of Pcap<i>CO</i><sub>2</sub> because the two parameters are highly correlated and there is no inconvenience to the patient.