Noninvasive monitoring of PaCO2 during one-lung ventilation and minimal access surgery in adults: End-tidal versus transcutaneous techniques

Background: Previous studies have suggested that end-tidal CO₂ (ET-CO₂ ) may be inaccurate during one-lung ventilation (OLV). This study was performed to compare the accuracy of the noninvasive monitoring of PCO₂ using transcutaneous CO₂ (TC-CO₂ ) with ET-CO₂ in patients undergoing video-assisted thoracoscopic surgery (VATS) during OLV.
Materials and Methods: In adult patients undergoing thoracoscopic surgical procedures, PCO₂ was simultaneously measured with TC-CO₂ and ET-CO₂ devices and compared with PaCO₂.
Results: The cohort for the study included 15 patients ranging in age from 19 to 71 years and in weight from 76 to 126 kg. During TLV, the difference between the TC-CO₂ and the PaCO₂ was 3.0 ± 1.8 mmHg and the difference between the ET-CO₂ and PaCO₂ was 6.2 ± 4.7 mmHg ( P =0.02). Linear regression analysis of TC-CO2 vs. PaCO₂ resulted in an r² = 0.6280 and a slope = 0.7650 ± 0.1428, while linear regression analysis of ET-CO₂ vs. PaCO₂ resulted in an r² = 0.05528 and a slope = 0.1986 ± 0.1883. During OLV, the difference between the TC-CO₂ and PaCO₂ was 3.5 ± 1.7 mmHg and the ET-CO₂ to PaCO₂ difference was 9.6 ± 3.6 mmHg (P =0.03 vs. ET-CO₂ to PaCO₂ difference during TLV; and P < 0.0001 vs. TC-CO₂ to PaCO₂ difference during OLV). In 13 of the 15 patients, the TC-CO₂ value was closer to the actual PaCO₂ than the ET-CO₂ value (P =0.0001). Linear regression analysis of TC-CO₂ vs. PaCO₂ resulted in an r² = 0.7827 and a slope = 0.8142 ± 0.0.07965, while linear regression analysis of ET-CO₂ vs. PaCO₂ resulted in an r² = 0.2989 and a slope = 0.3026 ± 0.08605.
Conclusions: During OLV, TC-CO₂ monitoring provides a better estimate of PaCO₂ than ET-CO2 in patients undergoing VATS.