Agreement Between Transcutaneous Monitoring and Arterial Blood Gases During COPD Exacerbation

Background: Transcutaneous measurements of CO₂ and O₂ ([Formula: see text], [Formula: see text]) are noninvasive and allow for continuous monitoring in adults with exacerbation of COPD, but substantial accuracy issues may exist. We investigated agreement between results of arterial blood gas analysis and transcutaneous measurements of CO₂ and O₂ in patients with COPD.

Methods: Adult subjects were monitored after acute admission to a respiratory intermediate care unit or ICU due to exacerbation of COPD and with ongoing noninvasive ventilation or immediately following extubation. Monitored variables were continuous transcutaneous measurement and simultaneous routine arterial blood gas analysis. Agreement between measurements was assessed by calculating bias with 95% limits of agreement for single-point estimates of [Formula: see text] versus [Formula: see text] and versus [Formula: see text], and for changes in transcutaneous measurements between 2 time points ([Formula: see text] and [Formula: see text]). We considered limits of agreement within ± 7.5 mm Hg to be acceptable.

Results: A total of 57 transcutaneous measurements were made in 20 subjects for comparison with concurrent arterial blood gas analysis at 36 time points. The bias (limits of agreement) for [Formula: see text] and [Formula: see text] was 2.5 mm Hg (-10.6 to 15.6 mm Hg) and 11.2 mm Hg (-28.2 to 50.6 mm Hg), respectively. The bias for [Formula: see text] and [Formula: see text] was 2.3 mm Hg (-3.8 to 8.3 mm Hg) and -5.3 mm Hg (-37.5 to 27 mm Hg), respectively.

Conclusions: [Formula: see text] and [Formula: see text] did not accurately reflect results from arterial blood gas analyses in this study of mostly hypercapnic subjects. Agreement between changes in CO₂ during the monitoring period was acceptable, however, and transcutaneous monitoring may be used for continuous monitoring of [Formula: see text] in conjunction with arterial blood gas analysis for reference.