Evaluation of a system for transcutaneous long-term capnometry

Background: The measurement of CO(2) partial pressure (PCO(2)) is of great importance. Former systems of transcutaneous capnometry combining the measurement of oxygen partial pressure (PO(2)) and PCO(2) had their limitations due to skin irritations caused by the heating-up of the sensor and a short application time of 4 h.

Objectives: To evaluate for the first time combined monitoring of transcutaneous PCO(2) (tcPCO(2)) and oxygen saturation applying a lower temperature (sensor temperature 42 degrees C) and a new sensor technology in healthy individuals during sleep.

Methods: 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). tcPCO(2) was continuously monitored and its correlation with selective measured capillary PCO(2) values (PcapCO(2)) was monitored at 0.00 and 4.00 h.

Results: At 0.00 h, PcapCO(2) was 37.1 +/- 5.1 mm Hg and tcPCO(2) was 43.4 +/- 6.6 mm Hg (p < 0.001). At 4.00 h, PcapCO(2) was 37.0 +/- 5.6 mm Hg and tcPCO(2) was 43.5 +/- 5.4 mm Hg (p < 0.001). PcapCO(2) and tcPCO(2) 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 tcPCO(2) values.

Conclusion: The investigated system enables stable measurement of tcPCO(2) without relevant drift in healthy individuals and does not require recalibration. tcPCO(2) is highly suitable as a measure of PcapCO(2) because the two parameters are highly correlated and there is no inconvenience to the patient.