Continuous non-invasive PCO2 monitoring in weaning patients: Transcutaneous is advantageous over end-tidal PCO2

Background and objective: Continuous partial pressure of carbon dioxide (PCO2) assessment is essential for the success of mechanical ventilation (MV). Non-invasive end-tidal PCO2 (PetCO(2)) and transcutaneous PCO2 (PtcCO(2)) measurements serve as alternatives to the gold standard arterial PCO2 (PaCO2) method, but their eligibility in critical care is unclear. Methods: The present study therefore performed methodological comparisons of PaCO2 versus PetCO(2) and PtcCO(2), respectively, in weaning patients receiving invasive MV via tracheal cannulas. PetCO(2) and PtcCO(2) were recorded continuously, while PaCO2 was analysed at baseline, and after 30 and 60 min. Using the BlandAltman analysis, a clinically acceptable range was defined as a mean difference of +/- 4 mm Hg between PaCO2 and non-invasive strategies. Results: A total of 60 patients (COPD (n = 30) and nonCOPD (n = 30)) completed the protocol. Mean PCO2 values were 42.4 +/- 8.6 mm Hg (PaCO2), 36.5 +/- 7.5 mm Hg (PetCO(2)) and 41.7 +/- 8.7 mm Hg (PtcCO(2)). Mean differences between PtcCO(2) and PaCO2 were -0.7 +/- 3.6 mm Hg (95% CI: -1.6/0.3 mm Hg; 95% limits of agreement: -7.8 to 6.4 mm Hg), and between PetCO(2) and PaCO2 -5.9 +/- 5.3 mm Hg (95% CI: -7.2/-4.5 mm Hg; 95% limits of agreement: -16.2 to 4.5 mm Hg). Underestimation of PaCO2 by PetCO(2) was most pronounced in COPD patients. Conclusion: Our data therefore support PtcCO(2) as a suitable means for monitoring PCO2 in patients undergoing invasive MV. This is in contrast to PetCO(2), which clearly underestimated PaCO2, especially in patients with COPD.