Transcutaneous Carbon Dioxide Pressure Monitoring in a Specialized Weaning Unit

Abstract

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.

Keywords

capnometry capnography carbon dioxide bronchoscopy physiologic monitoring weaning

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