• Douglas C Johnson, Salma Batool, and Ronald Dalbec.
• Spaulding Rehabilitation Hospital, 125 Nashua Street, Boston MA 02114, USA. djohnson5@partners.org
• Resp Care. 2008 Aug 1;53(8):1042-7.

ObjectiveTo evaluate transcutaneously measured P(CO(2)) (P(tcCO(2))) values during ventilator weaning and during bronchoscopies on ventilated patients, and to compare P(tcCO(2)) values to P(aCO(2)) values from arterial blood analysis and end-tidal P(CO(2)) (P(ETCO(2))) values from capnography.MethodsIn our specialized weaning unit we measured P(tcCO(2)) 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(ETCO(2)) measurements (39 measurements in 31 patients).ResultsThere were often large changes (> 10 mm Hg) in P(tcCO(2)) during daytime SBTs (23%) and the initial overnight off-the-ventilator periods (42%), which influenced the decisions of whether to continue the SBT. P(tcCO(2)) 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(aCO(2)) closely matched P(tcCO(2)) (mean +/- SD difference of 0.5 +/- 4.1 mm Hg). There was a greater difference between P(aCO(2)) and P(ETCO(2)) (3.7 +/- 7.7 mm Hg during prolonged exhalation, and 6.8 +/- 7.2 mm Hg during tidal breathing).ConclusionsMonitoring P(tcCO(2)) is very helpful in assessing and managing patients undergoing SBTs, during the first night off the ventilator, and during bronchoscopy on ventilated patients. P(tcCO(2)) more closely matches P(aCO(2)) than does P(ETCO(2)).

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