Concordance between transcutaneous and arterial measurements of carbon dioxide in an ED

Abstract

Background: Transcutaneous carbon dioxide pressure (PtcCO(2)) has been suggested as a noninvasive surrogate of arterial carbon dioxide pressure (PaCO(2)). Our study evaluates the reliability of this method in spontaneously breathing patients in an emergency department.

Patients and methods: A prospective, observational study was performed in nonintubated dyspneic patients who required measurement of arterial blood gases. Simultaneously and blindly to the physicians in charge, PtcCO(2) was measured using a TOSCA 500 monitor (Radiometer, Villeurbanne, France). Agreement between PaCO(2) and PtcCO(2) was assessed using the Bland-Altman method.

Results: Forty-eight patients (mean age, 65 years) were included, and 50 measurements were done. Eleven (23%) had acute heart failure; 10 (21%), pneumonia; 7 (15%), acute asthma; and 7 (15%), exacerbation of chronic obstructive pulmonary disease. Median PaCO(2) was 42 mm Hg (range, 17-109). Mean difference between PaCO(2) and PtcCO(2) was 1 mm Hg with 95% limits of agreement of -3.4 to +5.6 mm Hg. All measurement differences were within 5 mm Hg, and 32 (64%) were within 2 mm Hg.

Conclusion: Transcutaneous carbon dioxide pressure accurately predicts PaCO(2) in spontaneously breathing patients.