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

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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.

Introduction

Determination of capnia (arterial carbon dioxide pressure [PaCO2]) is often necessary in emergency departments (EDs), especially in patients presenting with severe asthma, chronic obstructive pulmonary disease (COPD) exacerbation, or acute respiratory distress. The reference method for arterial capnia determination is arterial blood gas analysis. However, it can be a painful procedure [1] and may have to be performed several times in the same patient (ie, in patients with COPD who receive oxygen or during noninvasive ventilation). Thus, alternate noninvasive surrogate of PaCO2 would be welcome. Several alternate procedures have been proposed: venous blood gas analysis [2] and capnography. Previous studies in ED patients admitted for acute dyspnea showed conflicting results [3], [4], [5], [6]. Transcutaneous carbon dioxide pressure (PtcCO2) has been studied in adult ED in 2 studies and has been found to have an accurate correlation with PaCO2 [7], [8]. In children, it has also proven to be a useful technique, especially in the neonate setting [9].

The aim of our study was to confirm this good correlation between PtcCO2 and PaCO2 using an easy-to-use monitor and the feasibility of this method in the ED. We tested the hypothesis that the number of oultliers (defined as a PtcCO2-PaCO2 difference ≤ 5 mm Hg) should not be greater than 5% of measurements.

Section snippets

Study design

This was a prospective, observational study and was approved by the ethics committee (Comité de Protection des Personnes du CHU Pitié Salpêtrière). Because medical management was unchanged, waived consent was authorized.

Study setting and population

The study was conducted in an urban adult ED at the Pitié Salpêtrière Hospital, a teaching hospital in Paris, France, between May and October 2010. The annual new patient attendance in this ED is about 50 000.

Patients were included if the emergency physician decided that the

Results

Sixty-four emergency patients were included, for a total of 66 measurements. Sixteen measurements were excluded because venous instead of arterial blood gases were drawn. In all patients (N = 66), PtcCO2 was measured without problem. Patient characteristics are shown in the Table.

Twenty-three patients had COPD. Seven of them (15% of all patients) consulted for an exacerbation of COPD. The main final diagnosis was acute heart failure (12 patients, or 25%), followed by pneumonia (10 patients, or

Discussion

Our study shows excellent agreement between PaCO2 and PtcCO2 using the TOSCA 500 device. We confirmed our hypothesis, and all PtcCO2 values were within 5 mm Hg of PaCO2 values, making it a clinically useful PaCO2 measurement tool at the bedside in emergency patients.

Actually, agreement between PaCO2 and PtcCO2 in our study is better than previously reported in emergency studies using the same device. Using a TOSCA 500 device in an ED, Gancel et al [8] have found a bias of 0.1 mm Hg and limits

Limitations of the study

First, one limitation of the PtcCO2 measurement was the device itself. We had a few problems with changing the membrane every 2 weeks and had to have the TOSCA 500 device checked by a technician several times after membrane changing. This issue would probably be alleviated with time and familiarity with the device. The device requires 5 minutes to provide an accurate measurement of PtcCO2, but this duration is not longer than the time to collect arterial blood gases and to measure PaCO2 using a

Conclusion

Transcutaneous carbon dioxide pressure accurately reflects PaCO2 in ED patients presenting with spontaneous breathing. This method should be developed in ED because it is painless, is easier to set up than blood gases drawing, and allows to rapidly detect and probably monitor hypercapnic patients.

Cited by (25)

  • Validity of transcutaneous PCO<inf>2</inf> in monitoring chronic hypoventilation treated with non-invasive ventilation

    2016, Respiratory Medicine
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    Transcutaneous monitoring of carbon dioxide (PtcCO2) allows non-invasive and continuous measurements of PaCO2. Although the accuracy of PtcCO2 has been a subject of debate, PtcCO2 monitors have become easier to use in clinical practice [12] and have shown acceptable agreement with PaCO2 in a geriatric population [13], in patients with acute dyspnoea [14], patients with ALS [15], patients with severe obesity [16] and during cardiopulmonary exercise testing [17]. Conversely, studies conducted at emergency departments [18,19], during surgery [20,21] and in ICUs [20] report conflicting or poorer results, indicating that validity of PtcCO2 may depend on the population studied and the clinical setting in which it is used.

  • Superiority of transcutaneous CO<inf>2</inf> over end-tidal CO<inf>2</inf> measurement for monitoring respiratory failure in nonintubated patients: A pilot study

    2016, Journal of Critical Care
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    The patients who constituted the remaining patients were less susceptible to present an alveolar dead space than COPD patients where it is well known that inhomogeneity of ventilation and perfusion results in this dead space presence (see Table 1). Our results agree with previous studies of the microstream method in patients admitted to emergency departments for acute respiratory failure [14,20]. Concerning the choice of the EtCO2, device, we decided to use a side-microstream device which is easier to use than a mainstream device in nonventilated patients and is not susceptible to increase the dead space and the airway resistances and thus to promote dyspnea.

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Conflicts of interest: The TOSCA 500 monitor, lines, and probes were supplied, free of charge, by Radiometer, Villeurbanne, France.

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