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

Abstract

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 (PetCO₂ ) and transcutaneous PCO₂ (PtcCO₂ ) 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 PetCO₂ and PtcCO₂ , respectively, in weaning patients receiving invasive MV via tracheal cannulas. PetCO₂ and PtcCO₂ were recorded continuously, while PaCO₂ was analysed at baseline, and after 30 and 60 min. Using the Bland-Altman 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 non-COPD (n = 30)) completed the protocol. Mean PCO₂ values were 42.4 ± 8.6 mm Hg (PaCO₂ ), 36.5 ± 7.5 mm Hg (PetCO₂ ) and 41.7 ± 8.7 mm Hg (PtcCO₂ ). Mean differences between PtcCO₂ 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 PetCO₂ 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 PetCO₂ was most pronounced in COPD patients.

Conclusion: Our data therefore support PtcCO₂ as a suitable means for monitoring PCO₂ in patients undergoing invasive MV. This is in contrast to PetCO₂ , which clearly underestimated PaCO₂ , especially in patients with COPD.

Keywords: blood gas analysis; end-tidal; partial pressure of carbon dioxide; respiratory failure; transcutaneous.