Transcutaneous Carbon Dioxide Pressure Monitoring in a Specialized Weaning Unit

OBJECTIVE: To evaluate transcutaneously measured P-CO2 (P-tcCO2) values during ventilator weaning and during bronchoscopies on ventilated patients, and to compare P-tcCO2, values to P-aCO2 values from arterial blood analysis and end-tidal P-CO2, (P-ETCO2) values from capnography. METHODS: In our specialized weaning unit we measured P-tcCO2 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 P-ETCO2, measurements (39 measurements in 31 patients). RESULTS: There were often large changes (> 10 mm Hg) in P-tcCO2 during daytime SBTs (23%) and the initial overnight off-the-ventilator periods (42%), which influenced the decisions of whether to continue the SBT. P-tcCO2 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. P-aCO2, closely matched P-tcCO2 (mean +/- SD difference of 0.5 +/- 4.1 mm Hg). There was a greater difference between P-aCo2 and P-ETCO2 (3.7 +/- 7.7 mm Hg during prolonged exhalation, and 6.8 +/- 7.2 mm Hg during tidal breathing). CONCLUSIONS: Monitoring P-tcCO2 is very helpful in assessing and managing patients undergoing SBTs, during the first night off the ventilator, and during bronchoscopy on ventilated patients. P-tcCO2, more closely matches P-aCO2 than does P-ETCO2.