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. The present trial was designed to investigate the potential roles of end‐tidal partial pressure of carbon dioxide (PetCO2) and transcutaneous partial pressure of carbon dioxide (PtcCO2) monitoring in patients with prolonged weaning, especially in COPD patients. The present study showed that PtcCO2 monitoring reflects the gold standard method of arterial partial pressure of carbon dioxide (PaCO2) measurements within predefined clinically acceptable range, while PetCO2 showed a systematic underestimation of PaCO2.