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

OBJECTIVE: To compare transcutaneous CO(2) (TCCO(2)) and end-tidal CO(2) (ETCO(2)) 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 ETCO(2) 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 PaCO(2) difference was 3.9 +/- 1.6 mmHg, whereas the TC to PaCO(2) difference was 2.5 +/- 0.8 mmHg (p = 0.0049). During OLV, the ET to PaCO(2) difference increased to 5.8 +/- 2.3 mmHg, whereas the TC to PaCO(2) difference was 2.7 +/- 1.4 mmHg (p = 0.0049 for ET to PaCO(2) difference during OLV v TLV and p = 0.0004 for ET to PaCO(2) gradient v TC to PaCO(2) gradient during OLV). During TLV, the difference between the ET and PaCO(2) was < or = 5 mmHg in 13 of 15 patients, whereas the difference between the TC and PaCO(2) was < or = 5 mmHg in 15 of 15 patients (p = not significant). During OLV, the difference between the ET and the PaCO(2) was < or = 5 mmHg in 6 of 15 patients, whereas the difference between the TC and PaCO(2) was < or = 5 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 PaCO(2) during TLV v OLV). CONCLUSIONS: During OLV, TCCO(2) monitoring provides a more accurate estimate of PaCO(2) than ET techniques.