Comparison of ear and chest probes in transcutaneous carbon dioxide pressure measurements during general anesthesia in adults
For transcutaneous carbon dioxide pressure (tcPCO2) measurement, the probe on the trunk or extremities has been used for many years. Our previous study showed that chest was better than arm for tcPCO2 monitoring. Recently, the ear probe has been developed. The accuracy of tcPCO2 as a surrogate measurement of arterial carbon dioxide pressure (PaCO2) has not been compared between the measurement with probe on the chest and measurement with probe on the earlobe. This study compared the accuracy of tcPCO2 measured on the chest and tcPCO2 measured on earlobe during general anesthesia in adults using linear regression analysis and Bland–Altman plot.
Ten patients aged 30–70 years scheduled for abdominal surgery under general anesthesia were enrolled. TcPCO2 by TCM4™ (Radiometer, Copenhagen, Denmark, TtcPCO2) with its probe on the chest, tcPCO2 by Sentec™ (Sentec AG, Therwil, Switzerland, StcPCO2) with ear probe, end-tidal carbon dioxide pressure (EtCO2), and PaCO2 were simultaneously measured at four different sets of EtCO2 levels in each patient. In total, 40 measurements were performed. The Scatter plot and Bland–Altman plot were obtained. Correlation coefficient (R2) ≥0.70 and limits of agreement ≤4 mmHg were judged as significant.
TtcPCO2 showed significant positive correlation with PaCO2 (R2 = 0.80) but StcPCO2 did not (R2 = 0.55). TtcPCO2 and PaCO2, and StcPCO2 and PaCO2 had large limits of agreement (−6.56 mmHg, 4.21 mmHg and −11.05 mmHg, 7.64 mmHg, respectively). TtcPCO2 and StcPCO2 had no significant correlation (R2 = 0.63) and large limits of agreement (−8.98 mmHg to 7.91 mmHg).
During general anesthesia in adults, both TtcPCO2 and StcPCO2 were not interchangeable with PaCO2, but only TtcPCO2 had good positive correlation with PaCO2.