OBJECTIVE: To evaluate transcutaneously measured PCO2(PtcCO2) values during ventilator weaning and during bronchoscopies on ventilated patients, and to compare PtcCO2 values to PaCO2 values from arterial blood analysis and end-tidal PCO2
(PETCO2) values from capnography. METHODS: In our specialized weaning unit we measured PtcCO2 in tracheostomized patients with prolonged weaning failure during daytime spontaneous breathing trials (SBTs) (23 measurement sessions in 15 patients), during their first nights
off the ventilator (12 measurement sessions in 12 patients), during bronchoscopy while ventilated (80 measurement sessions in 21 patients), simultaneous with arterial blood draw for blood gas analysis (48 measurements in 38 patients), and simultaneous with PETCO2 measurements (39
measurements in 31 patients). RESULTS: There were often large changes (> 10 mm Hg) in PtcCO2 during daytime SBTs (23%) and the initial overnight off-the-ventilator periods (42%), which influenced the decisions of whether to continue the SBT. PtcCO2 often rose during
bronchoscopy (mean ± SD increase of 10.7 ± 5.8 mm Hg), which influenced the physician to change the ventilator settings 44% of the time. PaCO2 closely matched PtcCO2 (mean ± SD difference of 0.5 ± 4.1 mm Hg). There was a greater difference
between PaCO2 and PETCO2 (3.7 ± 7.7 mm Hg during prolonged exhalation, and 6.8 ± 7.2 mm Hg during tidal breathing). CONCLUSIONS: Monitoring PtcCO2 is very helpful in assessing and managing patients undergoing SBTs, during the first night off the
ventilator, and during bronchoscopy on ventilated patients. PtcCO2 more closely matches PaCO2 than does PETCO2.