Use of end-tidal PCO2 and transcutaneous PCO2 as noninvasive measurement of arterial PCO2 in extubated patients recovering from general anesthesia.

This study was designed to assess the accuracy of end-tidal PCO2 and transcutaneous PCO2 as measurements of arterial PCO2 in extubated, spontaneously breathing patients recovering from general anesthesia. In 30 patients, measurement of arterial transcutaneous, and end-tidal PCO2 were taken simultaneously with body temperature approximately every 15 minutes over a 2-hour period. Arterial PCO2 values were corrected for body temperature. Values for PaCO2 were compared with those for PETCO2 and PsCO2 by linear regression analysis and by calculation of bias +/- precision. Thirty-six percent of the capnogram tracings obtained did not develop a plateau phase. We found poor correlation between end-tidal and arterial PCO2 regardless of the shape of the capnogram tracing, as well as poor correlation between transcutaneous and arterial PCO2. Although the measurements of bias and precision of noninvasive PCO2 monitors in this population are comparable to studies in other populations, we advise caution in relying on the routine use of PETCO2 or PsCO2 for the noninvasive assessment of respiratory depression in extubated, spontaneously breathing patients recovering from general anesthesia.