Comparison of prolonged exhalation end-tidal CO₂ and transcutaneous CO₂ monitoring in COPD patients.

BACKGROUND

Noninvasive evaluation of partial pressure of carbon dioxide (PCO2) is clinically important for screening and monitoring of hypercapnia, especially in patients with chronic obstructive pulmonary disease (COPD). However, the comparative accuracy of end-tidal PCO2 (PetCO2) and transcutaneous PCO2 (PtcCO2) monitoring in COPD remains uncertain. This study aimed to evaluate the agreement between PetCO2 obtained by using modified method of prolonged expiration with an integrated calculation algorithm (PetCO2-PA) and PtcCO2 with arterial PCO2 (PaCO2) in patients with COPD.

METHODS

In this single-center study, 83 patients with COPD (48 at stable phase and 35 during acute exacerbation) underwent arterial blood gas (ABG) analysis followed with simultaneous measurement of PetCO2-PA and PtcCO2. Agreement between different measurements was assessed using Bland-Altman analysis (bias and limits of agreement (LOA)), and intraclass correlation coefficients. The receiver operating characteristic curve was used for evaluation of ability to detect hypercapnia, defined as PaCO2 ≥ 45 mmHg and ≥ 50 mmHg.

RESULTS

Bland-Altman analysis revealed a small bias of - 1.7 mmHg but a relatively wide LOA of - 8.6 to 5.1 for PtcCO2 and - 2.4 mmHg (LOA: - 9.9 to 5.1) for PetCO2-PA. The similar results were observed across disease states (stable vs. exacerbation) and degrees of hypercapnia. PetCO2-PA and PtcCO2 exhibited comparably diagnostic accuracy for hypercapnia (PaCO2 ≥ 45 or 50 mmHg), each achieving an area under the curve (AUC) greater than 0.94, with no statistically significant inter-method differences. The proportions of measurements exceeding the clinical acceptability thresholds of ± 4 mmHg and ± 7 mmHg did not differ significantly between techniques.

CONCLUSION

PetCO2-PA demonstrated a small bias but a relatively wide LOA with PaCO2, non-inferior to PtcCO2, in patients with COPD. Owing to its cost-effectiveness, rapid operation, and portability, PetCO2-PA represented a practical alternative for screening and monitoring of hypercapnia in COPD patients.

CLINICAL TRIAL REGISTRATION: The trial was registered at ClinicalTrials.gov (identifier: NCT04051931).