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.