Noninvasive carbon dioxide monitoring during one-lung ventilation: End-tidal versus transcutaneous techniques

Objective: To compare transcutaneous CO2 (TCCO2) and end-tidal CO2 (ETCO2) monitoring during one-lung ventilation (OLV). Design: Prospective study. Setting: Operating room of a University Hospital. Participants: Fifteen patients undergoing thoracic surgical procedures in whom one-lung ventilation was deemed necessary. Intervention: TC and ETCO2 monitors were used simultaneously in the patients and compared with arterial blood gases (ABGs) during 2-lung ventilation and OLV. Measurements and Main Results: During 2-lung ventilation (TLV), the ET to PaCO2 difference was 3.9 +/- 1.6 mmHg, whereas the TC to PaCO2 difference was 2.5 +/- 0.8 mmHg (p = 0.0049). During OLV, the ET to PaCO2 difference increased to 5.8 +/- 2.3 mmHg, whereas the TC to PaCO2 difference was 2.7 +/- 1.4 mmHg (p = 0.0049 for ET to PaCO2 difference during OLV v TLV and p = 0.0004 for ET to PaCO2 gradient v TC to PaCO2 gradient during OLV). During TLV, the difference between the ET and PaCO2 was less than or equal to5 mmHg in 13 of 15 patients, whereas the difference between the TC and PaCO2 was less than or equal to5 mmHg in 15 of 15 patients (p = not significant). During OLV, the difference between the ET and the PaCO2 was less than or equal to5 mmHg in 6 of 15 patients, whereas the difference between the TC and PaCO2 was:55 mmHg in 14 of 15 patients (p = 0.0052, odds ratio 21.0 for ET v TC techniques and p = 0.02, odds ratio 9.75 for ET to PaCO2 during TLV v OLV). Conclusions: During OLV, TCCO2 monitoring provides a more accurate estimate of PaCO2 than ET techniques. (C) 2003 Elsevier Inc. All rights reserved.