Brief Report
Concordance between capnography and capnia in adults admitted for acute dyspnea in an ED

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Abstract

Background

End-tidal carbon dioxide pressure (etCO2) is widely used in anaesthesia and critical care in intubated patients. The aim of our preliminary study was to evaluate the feasibility of a simple device to predict capnia in spontaneously breathing patients in an emergency department (ED).

Patients and methods

This study was a prospective, nonblind study performed in our teaching hospital ED. We included nonintubated patients with dyspnea (≥18 years) requiring measurement of arterial blood gases, as ordered by the emergency physician in charge. There were no exclusion criteria. End-tidal CO2 was measured by an easy-to-use device connected to a microstream capnometer, which gave a continuous measurement and graphical display of the etCO2 level of a patient's exhaled breath.

Results

A total of 43 patients (48 measurements) were included, and the majority had pneumonia (n = 12), acute cardiac failure (n = 8), asthma (n = 7), or chronic obstructive pulmonary disease exacerbation (n = 6). Using simple linear regression, the correlation between etCO2 and Paco2 was good (R = 0.82). However, 18 measurements (38%) had a difference between etCO2 and Paco2 of 10 mm Hg or more. The mean difference between the Paco2 and etCO2 levels was 8 mm Hg. Using the Bland and Altman matrix, the limits of agreement were −10 to +26 mm Hg.

Conclusion

In our preliminary study, etCO2 using a microstream method does not seem to accurately predict Paco2 in patients presenting to an ED for acute dyspnea.

Introduction

Capnia (Paco2) is frequently performed in patients with acute respiratory distress in the emergency department (ED). It is very useful to assess—or to follow—a patient's breathing quality, especially in severe acute asthma or chronic obstructive pulmonary disease (COPD) exacerbation. However, it is a painful procedure [1].

Now, capnography is widely used in operating rooms and intensive care units. Thus, end-tidal carbon dioxide pressure (etCO2) is the gold standard for confirming the correct placement of the endotracheal tube [2], [3], [4]. It is also very helpful in cardiac resuscitation. Indeed, studies have shown that etCO2 values were a good indicator of the effectiveness of cardiac compression for predicting survival in cardiac arrest [5], [6]. It is also recommended for prehospital monitoring of patients with severe head trauma [7], [8]. There are few studies performed in nonintubated patients, especially in ED adults [9], especially those with acute dyspnea. Corbo et al [10] demonstrated a high concordance between etCO2 measured by capnography and Paco2 measured by arterial blood gas in emergency patients with asthma. However, they used a complicated device. Thus, the aim of our preliminary study was to evaluate the feasibility of a new and simple device (microstream) to predict capnia in spontaneously breathing patients in an ED.

Section snippets

Ethics

This study was performed in accordance with the ethical standards of the responsible committee on human experimentation (institutional or regional) and with the Helsinki declaration of 1975, as revised in 1983. This study was approved by the ethical committee of our hospital. Waived informed consent was authorized because routine care of the patient was not modified. However, all the patients were informed of the use of this new device.

Method

End-tidal CO2 was measured by an easy-to-use device:

Results

We included 43 patients admitted in our ED for acute dyspnea or acute respiratory distress and performed 48 measurements. The main characteristics of the patients are detailed in Table 1. Most patients had pneumonia, acute cardiac failure, asthma, or COPD exacerbation.

The mean difference between Paco2 and etCO2 was 8 ± 10 mm Hg, and the median value was 6 mm Hg (with differences varying from −12 to 41 mm Hg).

However, of 48 measurements, 18 (38%) had an etCO2 within 5 mm Hg of Paco2 and 18

Discussion

In our study, the correlation between etCO2 and Paco2 was much lower than in a previous study focusing on acute exacerbation of emergency asthma [10]. End-tidal CO2 measured through our device was not accurate enough to predict Paco2 in patients presenting to an ED for acute dyspnea.

In Corbo's study, patients with asthma (except for 1 patient) had an etCO2 within 5 mm Hg of their Paco2. In fact, they used a different method to measure etCO2 through an airway adapter using a mouthpiece, which

Limitations

There are several limitations to our study. Although, the result of the Paco2 was blinded to the technician who performed the arterial blood gas analysis, the investigator knew the result of the Paco2 when he or she used the device for measuring etCO2. Because of our small number of patients, we could not distinguish a subgroup of patients for whom etCO2 was an accurate predictor of etCO2. A study focusing on patients with few etCO2-Paco2 mismatch factors would be of interest for evaluating if

Conclusion

End-tidal CO2 measured through a SmartCapnoline Plus device using a microstream method does not accurately predict Paco2 in patients presenting to an ED for acute dyspnea. Further studies are warranted to evaluate such a device specifically in obstructive respiratory diseases in adults and for following serial capnia. We are currently performing these 2 studies.

References (20)

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