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Fig. 1
Linear correlation between transcutaneous PtcCO2 and PaCO2. Regression line is the continuous line; 95% CI lines, dotted lines.
Fig. 2
Bland-Altman representation of comparison analysis between PaCO2 and PtcCO2 vs means of paired measurements. The bias is shown as continuous line; limits of agreement (bias ±1.95 SD), dashed lines; and the shaded area, the outlier limits (±5 mm Hg).
Abstract
Background
Transcutaneous carbon dioxide pressure (PtcCO2) has been suggested as a noninvasive surrogate of arterial carbon dioxide pressure (PaCO2). 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, PtcCO2 was measured using a TOSCA 500 monitor (Radiometer, Villeurbanne, France). Agreement between PaCO2 and PtcCO2 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 PaCO2 was 42 mm Hg (range, 17-109). Mean difference between PaCO2 and PtcCO2 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 PaCO2 in spontaneously breathing patients.
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☆Conflicts of interest: The TOSCA 500 monitor, lines, and probes were supplied, free of charge, by Radiometer, Villeurbanne, France.
