Abstract
Introduction: Few studies have investigated the use of transcutaneous CO2 (PtcCO2) measurement in patients with severe COPD and chronic respiratory insufficiency. Here, changes in CO2 levels may have clinical implications but the ability of the technique to describe acute changes remains undescribed.
Aims:
Compare acute change in arterial CO2 (PaCO2) and PtcCO2
Assess practical problems using the transdermal CO2 monitor over time
Method: Twelve patients, with COPD all in need of long-term oxygen therapy were included. A transdermal CO2 probe (V-sign, SenTec AG) was placed at the earlobe of the patient 30 minutes before study start to secure steady state. In two blocks of 30 minutes, inspired oxygen level was initially lowered and following this increased. PtcCO2 was measured whilst PaCO2 was sampled from an arterial line. A total of 20 blood samples were obtained per patient.
Results: Acute fast changes in CO2 between samples, was calculated as absolute rate change (kPa/min). The mean rate of change (+/- SD) for PaCO2 was 0.15 kPa +/-0.45 and 0.05 kPa +/-0.14 for PtcCO2. The accuracy of the PtcCO2 measurement was -0.195 kPa, and precision 0.67 kPa, both consistent with previous studies. In one patient, the PtcCO2 measurements were not accomplished due to technical problems. There were no incidents of burns during the 90 minutes the ear probe was attached.
Conclusion: Fast acute changes in PaCO2 are only slowly followed by PtcCO2. Thus, a transcutaneous probe may not be optimal for tracking acute changes in CO2. There were no major practical problems utilizing the equipment.
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