Transcutaneous Measuring PCO 2 in COPD Patients in the Outpatient Setting

Abstract

Background:

Invasive measurement of PCO₂ is frequently obtained and necessary in guiding care in patients presenting with an exacerbation of COPD but rare in the outpatient setting to evaluate hypercapnia in stable COPD patients. Transcutaneous CO₂ monitoring (TcPCO₂) in the clinic setting for COPD patients is often measured when evaluating those using NIV during sleep but may also serve as a viable alternative to assess hypercapnia in stable patients with COPD. We aim to evaluate the novel use of TcPCO₂ measurement during COPD clinic visits.

Methods:

A retrospective chart analysis was performed on 30 COPD patients with TcPCO₂ measurements seen in the UC Davis COPD Clinic between November 2021 and May 2022. TcPCO₂ monitoring was performed with the Sentec Digital Monitoring System with the sensor application using a multi-site attachment ring. The sensor was placed on either the forehead or upper arm at 42 degrees Celsius per manufacturer guidelines. TcPCO₂ levels were documented once stabilization of PCO₂ was reached. Our primary objective was correlation between TcPCO₂ measurement and COPD stage or classification. Secondary assessments were differences in BMI, sex, %RV, symptomology scores, and exacerbation rates. Descriptive statistical analysis was performed with Chi square, Student t-test, and 95% confidence intervals when appropriate.

Results:

Of the 30 COPD patients with TcPCO₂ measurements, 59% (n = 19) had TcPCO₂ of ≤45 mm Hg (M = 40 mm Hg ± 3.4) and 41% (n = 12) had TcPCO₂ >45 mm Hg (M = 57.8 mm Hg ± 9.8). Of the patients with a TcPCO₂ reading of ≤45 mm Hg, 19% (n = 4) were GOLD class A, 28% (n = 6) were GOLD class B, 52% (n = 11) were GOLD class D. In those with >45 mm Hg readings, 33% (n = 4) were GOLD class B and 67% (n = 8) were GOLD Class D. There was no correlation between TcPCO₂ levels and GOLD classification of COPD, P = .27. Mean COPD stage for patients with a TcPCO₂ reading of ≤45 mm Hg was 2.9 (± 1.0) vs. 2.8 (± 0.7), P = .57. We also observed no correlation between TcPCO₂ levels ≤45 mm Hg and >45 mm Hg with BMI (P = .25), sex (P = .31), or exacerbation rates (P = .63). We also found no difference in %RV (P = .56) and symptomology scores (P = .86).

Conclusions:

No correlation was found in TcPCO₂ measurements and COPD stage, GOLD classification, or any secondary finding. Due to the limited sample size, further research is warranted. Lack of correlation may attest to evaluation of PCO₂ in any patient with COPD for consideration of necessary interventions (eg, sleep study referrals or NIV) to promote individualized therapy.