Transcutaneous CO₂ Measurement of COPD Patients in the Outpatient Setting

Abstract

Background: CO₂ is used in acute care settings to guide care for patients with exacerbations of COPD but less common in outpatient settings to evaluate hypercapnia in stable COPD. Transcutaneous CO₂ (PtcCO₂) monitoring may serve to assess hypercapnia during clinic visits. We previously published outcomes on 30 COPD patients seen in our clinic and found no correlation of PtcCO₂levels in GOLD classification, COPD stages, or other secondary findings. This study continues the evaluation of novel use of PtcCO₂measurement in patients referred to our COPD clinic.

Methods: A retrospective chart analysis was performed on 132 COPD patients with PtcCO₂measurements seen in the UC Davis Comprehensive COPD Clinic between November 2021 and February 2023. PtcCO₂monitoring was performed utilizing the Sentec Digital Monitoring System with the sensor application that uses a multi-site attachment ring. The sensor was placed on either the forehead or upper arm at 42°C per manufacturer guidelines. PtcCO₂levels were documented once stabilization of PCO₂ was reached. Our primary objective was correlation between PtcCO₂measurement and COPD stage and GOLD classification. Secondary assessments of BMI, exacerbation rates, %RV, symptomology scores, and oxygenation were evaluated. Descriptive statistical analysis was performed with Chi square and student t-test when appropriate.

Results: Of 132 COPD patients with spirometry 59% (n = 78) had PtcCO₂of ≤45 mm Hg and 41% (n = 54) had PtcCO₂>45 mm Hg. Of the patients with a PtcCO₂reading of ≤45 mm Hg, 44% (n = 11) had stage 1 COPD, 45% (n = 28) had stage 2, 24% (n = 15) had stage 3, and 13% (n = 8) had stage 4. In those with >45 mm Hg readings, 9% (n = 2) had stage 1 COPD, 36% (n = 16) were stage 2, 43% (n = 19) were stage 3, and 16% (n = 7) were stage 4. There were demonstrated differences between the two PtcCO₂groups and COPD stage (P = .042) but no correlation between PtcCO₂levels and GOLD classification of COPD (P = .45). Secondary outcomes for BMI (P = .19), exacerbation rates (P = .47), %RV (P = .24) and symptom scores (P = .93) did not show differences. Oxygen was utilized in 38% (n = 30) of patients with ≤45 mm Hg PtcCO₂and 57% (n = 31) of patients with >45 mm Hg readings (P = <.001).

Conclusions: There were statistically significant differences in COPD stages and supplemental oxygen use between the ≤45 mm Hg and >45 mm Hg PtcCO₂. No correlation was found in GOLD classification, BMI, exacerbation rates, %RV, symptomology scores in the two PtcCO₂cohorts.