American Journal of Emergency Medicine (2012) 30, 358-361

Brief Report

Can mainstream end-tidal carbon dioxide measurement accurately predict the arterial carbon dioxide level of patients with acute dyspnea in ED

Orhan Cinar MD?, Yahya Ayhan Acar MD, Ibrahim Arziman MD, Erden Kilic MD, Yusuf Emrah Eyi MD, Ramazan Ocal MD

Department of Emergency Medicine, Gulhane Military Medical Academy, GATA Acil Tip AD.06018 Etlik, Ankara, Turkey

Received 1 October 2010; revised 8 December 2010; accepted 8 December 2010

Abstract

Objective: This study was designed to determine whether the mainstream end-tidal carbon dioxide (ETCO₂) measurement can accurately predict the partial arterial carbon dioxide (PaCO2) level of patients presented to emergency department (ED) with acute dyspnea.

Methods: This prospective, observational study was conducted at a university hospital ED, which serves more than 110 000 patients annually. Nonintubated adult patients presented with acute dyspnea who required arterial blood gas analysis were recruited in the study for a 6-month period between January and July 2010. Patients were asked to breathe through an airway adapter attached to the mainstream capnometer. Arterial blood gas samples were obtained simultaneously.

Results: We included 162 patients during the study period. The mean ETCO₂ level was 39.47 +-

10.84 mm Hg (minimum, 19 mm Hg; maximum, 82 mm Hg), and Mean PaCO2 level was 38.95 +-

12.27 mm Hg (minimum, 16 mm Hg; maximum, 94 mm Hg). There was a positive, strong, statistically significant correlation between ETCO₂ and PaCO2 (r = 0.911, P b .001). The Bland-Altman plot shows the mean bias +- SD between ETCO₂ and PaCO2 as 0.5 +- 5 mm Hg (95% confidence interval, -1.3165- 0.2680) and the limits of agreement as -10.5 and +9.5 mm Hg. Eighty percent (n = 129) of the ETCO₂ measurements were between the range of +-5 mm Hg.

Conclusion: Mainstream ETCO₂ measurement accurately predicts the arterial PaCO2 of patients presented to ED with acute dyspnea. Further studies comparing mainstream and sidestream methods in these patients are required.

(C) 2012

Introduction

* Corresponding author. Tel.: +1 00905063699794.

E-mail addresses: [email protected] (O. Cinar), [email protected] (Y.A. Acar), [email protected]

(I. Arziman), [email protected] (E. Kilic), [email protected] (Y.E. Eyi), [email protected] (R. Ocal).

End-tidal carbon dioxide (ETCO₂) measurement is widely used in clinical practice because it is a noninvasive method that helps to assess the ventilatory status of the patient [1]. It has become the standard procedure for patient monitoring during anesthesia [2] and recently found its use in the emergency department (ED) for confirmation of the

0735-6757/$ - see front matter (C) 2012 doi:10.1016/j.ajem.2010.12.014

Mainstream ETCO₂ and PaCO2 in dyspnea patients

endotracheal tube position [3], procedural sedation analgesia [4,5], cardiopulmonary resuscitation [6,7], and follow-up of

2.2. Study protocol

359

patients with head trauma [8]. However, its use in dyspneic patients in ED has been avoided because of the concern that ETCO₂ measurement may not correlate with the partial arterial carbon dioxide (PaCO2) level of these patients because of ventilation-perfusion abnormalities caused by their existing pathologies. Studies focused on correlation between ETCO₂ and PaCO2 levels of dyspneic patients presented to ED have shown inconsistent findings, and there seems to be no consensus at present. Inconsistent findings of previous studies may be the result of incomparable patient groups included or different methods used for ETCO₂ measurement [9-12].

End-tidal carbon dioxide can be measured by 2 methods depending on the location of the photodetector or sensor: sidestream and mainstream. In the mainstream units, the sensor is placed directly in the patient’s breathing circuit. In the sidestream units, gas is aspirated continuously through microtubing to the sensor that is remote from the patient’s airway. Mainstream units have been especially developed for intubated patients. The major advantage of this technology is the almost instantaneous gas analysis (“first breath analy- sis”). Sidestream units have the advantage of continuous monitoring of ETCO₂, and the patients do not need to be intubated. However, its major disadvantage is that sampling tubing may be occluded with water and secretions, and analyses may take longer. These systems also increase the dead space that can sometimes cause misleading results [9]. Although mainstream devices have been developed for intubated patients, they may be also used to measure ETCO₂ level in compliant patients who may be able to blow into the sample tube 4 to 5 times.

We thought of the technical limitations of sidestream systems as the possible causes of conflicting results in previous reports. A large-scale study using the mainstream method may clarify the issue. Thus, the present study was designed to determine whether mainstream ETCO₂ mea- surement can accurately predict the PaCO2 level of patients presented to ED with acute dyspnea.

Methods

Study settings and population

This prospective, observational study was conducted at a university hospital ED, which serves more than 110 000 patients annually. The hospital institutional review board approved the study, and written informed consent for participation was obtained from all patients. All nonintubated adult patients presented with acute dyspnea who required arterial blood gas analysis were recruited in the study for a 6-month period between January and July 2010.

Patients were asked to breathe through an airway adapter attached to the capnometer. Arterial blood gas samples were obtained simultaneously. End-tidal carbon dioxide value was recorded while the arterial blood was pulsing in the syringe. End-tidal carbon dioxide measurement was performed with EMMA Emergency Capnometer (PHASEIN AB, Danderyd, Sweden), and Critical Care Xpress (Nova Biomedical Waltham, MA) was used for blood gas analyses. The ETCO₂ measurements were performed by the specially trained senior emergency medicine residents. A standard review chart was used for recording demographic character- istics of the patients including age, sex, respiratory rate, body temperature, pulse rate, arterial blood pressure, oxygen saturation, final diagnosis, and admissions.

2.3. Statistical analysis

Statistical analyses were performed by SPSS for Win- dows version 15.0 (SPSS Inc, Chicago, IL) and MedCalc

11.3 (MedCalc Software, Mariakerke, Belgium). Results are given as mean +- SD for continuous variables and as numbers and percentages for qualitative variables. The Pearson correlation coefficient was used to demonstrate the linear relationship between ETCO₂ and PaCO2 values. Bland- Altman analysis was used to determine the agreement between 2 methods. Limits of agreement were set at

+-1.96 mm Hg. All statistical comparisons were 2 tailed, and ? critical value of .05 was accepted as significant.

Results

We included 162 patients during the study period. The mean age was 62.4 +- 18.5 years, and 76 patients (46%) were

Table 1 Main characteristics of the patients (n = 162)

Characteristics

Age (y) Sex, male

Clinical characteristics Respiratory rate (breaths/min)

Value

62.4 +- 18.5

76 (46%)

26 +- 6

Body temperature (?C)	37 +- 4
Pulse rate (beats/min)	91 +- 22
Systolic arterial blood pressure (mm Hg)	146 +- 30
Diastolic arterial blood pressure (mm Hg)	82 +- 16
Oxygen Saturation (%)	88 +- 10
Final diagnosis COPD exacerbation	55 (33%)
Congestive heart failure	33 (20%)
Pneumonia	33 (20%)
Asthma	8 (4%)
Hospital admission	55 (33%)

360 O. Cinar et al.

men. Main characteristics of the patients are shown in Table 1. The mean ETCO₂ level was 39.47 +- 10.84 mm Hg (minimum, 19 mm Hg; maximum, 82 mm Hg), and mean PaCO2 level was 38.95 +- 12.27 mm Hg (minimum, 16 mm Hg; maximum, 94 mm Hg). There was a positive, strong, statistically significant correlation between ETCO₂ and PaCO2 (r = 0.911, P b .001, n = 162) (Fig. 1). The Bland-

Altman plot shows the mean bias +- SD between ETCO₂ and PaCO2 as 0.5 +- 5 mm Hg (95% CI, -1.3165-0.2680) and the

limits of agreement as -10.5 and +9.5 mm Hg (Fig. 2).

Eighty percent (n = 129) of the ETCO₂ measurements were between the range of +-5 mm Hg. There was no significant difference in subgroup analyses of patients according to the final diagnosis.

Discussion

In contrast to recent reports, our study showed that ETCO₂ measurement had high correlation (r = 0.911) and agreement (0.5 +- 5 mm Hg, between -10.5 and +9.5 mm Hg) with PaCO2 levels. Eighty percent (n = 129) of the ETCO₂ measurements were between the range of +-5 mm Hg, which could be acceptable for clinical use. In their study on 43 patients presented to ED with dyspnea, Delerme et al [10] have also showed a high correlation for ETCO₂/PaCO2 (R = 0.82) and found a difference of 8 mm Hg, which they defined the agreement as inadequate. The limits of agreements were reported as -10 to +26, and just 38% of the measurements were between the range of +-5 mm Hg. In a similar study on

50 home-care patients, Jabre et al [11] reported a poor agreement between 2 tests (12 +- 8 mm Hg). They found that only 16% of the measurements were between the range of

+-5 mm Hg. Kartal et al [12] reported a difference of 8.4 +-

11.1 mm Hg in their study on 118 patients with chronic obstructive pulmonary disease. The limits of agreements

100,00

80,00

60,00

PaCO2

40,00

20,00

Fig. 2 Bland-Altman plot of ETCO₂ compared with PaCO2.

were reported as -13 to +30. Sidestream method was used in these 3 recently published studies [10-12]. Sidestream method is a relatively new technique developed for Nonintubated patients, which has several technical limita- tions such as increased dead space, risk of occlusion by water and secretions, dilution of the aspirated air that may lead to lower results, and the need for patient’s mouth to be closed, all of which may contribute to these inconsistent results.

On the other side, looking back to earlier studies where mainstream method was used, one can find that Corbo et al

[13] have described a high agreement between 2 methods on 39 patients with asthma (mean difference, 1 mm Hg; range,

-0.1 to 2 mm Hg). Ninety-five percent of the ETCO₂

measurements were reported between the range of +-5 mm Hg. Direct contact with breath in mainstream method is expected to reduce measurement errors. However, this method is used for intubated patients, requires extra cooperation for nonintubated patients, and hinders the possibility of continuous monitoring, each of which prevents its use in various clinical conditions.

Two studies focused on dyspneic patients in ED have reported a high correlation for ETCO₂/PaCO2 (R = 0.79 and R = 0.77, respectively), but results of these studies were not reviewed in the “Discussion” section because authors have only assessed linear correlation and did not verify the agreement of methods by Bland-Altman method [14,15].

In their study, comparing the mainstream and sidestream methods in patients admitted to the postanesthesia care unit, Kasuya et al [16] measured the mean difference of ETCO₂/ PaCO2 as 3.5 +- 2.6 by mainstream method, which was increased to 7.3 +- 3.5 with sidestream method. This result showing better correlation of ETCO₂ and PaCO2 with mainstream method supports our study, which is in contrast with previous studies. They used a new capnograph model (cap-ONE; Nihon Kohden, Tokyo, Japan) that was designed for nonintubated patients. This new device, weighing only 30 g, does not require the patient to be intubated nor the nonintubated patient to blow through a tube.

0,00

20,00

40,00

60,00

80,00

Although mainstream method seems to provide more

ETCO2 (mm/Hg)

Fig. 1 Linear correlation between ETCO₂ and PaCO2.

accurate results compared with sidestream method, further studies comparing these 2 methods in dyspneic patients presented to ED are required to draw a solid conclusion.

Mainstream ETCO₂ and PaCO2 in dyspnea patients

We have not corrected PaCO2 levels for body temperature and respiratory rate, which stands as a limitation of our study. Another important limitation of our study was the degree of respiratory distress among the patients. Because we included all the dyspneic patients who required arterial blood gas analysis, patients who were not severely distressed were also included in this study. This might mean that our results cannot be extrapolated to a population with more severe disease.

Conclusion

Mainstream ETCO₂ measurement accurately predicts the PaCO2 level of patients who presented to ED with acute dyspnea. Further studies comparing mainstream and side- stream methods in these patients are required.

References

1. Nagler J, Krauss B. Capnography: a valuable tool for airway management. Emerg Med Clin North Am 2008;26:881-97.
2. Takki S, Aromaa U, Kauste A. The validity and usefulness of the end- tidal pCO2 during anaesthesia. Ann Clin Res 1972;4:278-84.
3. O’Connor RE, Swor RA. Verification of endotracheal tube placement

following intubation. National Association of EMS Physicians Standards and Clinical Practice Committee. Prehosp Emerg Care 1999;3:248-50.

1. Lightdale JR, Goldmann DA, Feldman HA, et al. Microstream capnography improves patient monitoring during moderate sedation: a randomized, controlled trial. Pediatrics 2006;117:e1170-8.

361

1. Krauss B, Hess DR. Capnography for Procedural sedation and analgesia in the emergency department. Ann Emerg Med 2007;50: 172-81.
2. Levine RL, Wayne MA, Miller CC. End-tidal carbon dioxide and outcome of out-of-hospital cardiac arrest. N Engl J Med 1997;337: 301-6.
3. Steedman DJ, Robertson CE. Measurement of end-tidal carbon dioxide concentration during cardiopulmonary resuscitation. Arch Emerg Med 1990;7:129-34.
4. Helm M, Schuster R, Hauke J, et al. Tight control of prehospital ventilation by capnography in major Trauma victims. Br J Anaesth 2003;90:327-32.
5. Block Jr FE, McDonald JS. Sidestream versus mainstream carbon dioxide analyzers. J Clin Monit 1992;8:139-41.
6. Delerme S, Freund Y, Renault R, et al. Concordance between capnography and capnia in adults admitted for acute dyspnea in an ED. Am J Emerg Med 2010;28:711-4.
7. Jabre P, Jacob L, Auger H, et al. Capnography monitoring in nonintubated patients with respiratory distress. Am J Emerg Med 2009;27:1056-9.
8. Kartal M, Goksu E, Eray O, et al, The value of ETCO2 measurement for COPD patients in the emergency department. Eur J Emerg Med. doi:0.1097/MEJ.0b013e328337b9b9.
9. Corbo J, Bijur P, Lahn M, et al. Concordance between capnography and arterial blood gas measurements of carbon dioxide in acute asthma. Ann Emerg Med 2005;46:323-7.
10. Yosefy C, Hay E, Nasri Y, et al. End tidal carbon dioxide as a predictor of the arterial Pco2 in the emergency department setting. Emerg Med J 2004;21:557-9.
11. Barton CW, Wang ES. Correlation of end-tidal CO₂ measurements to arterial PaCO2 in nonintubated patients. Ann Emerg Med 1994;23: 560-3.
12. Kasuya Y, Akca O, Sessler DI, et al. Accuracy of postoperative end- tidal PCO2 measurements with mainstream and sidestream capnogra- phy in non-obese patients and in obese patients with and without obstructive Sleep apnea. Anesthesiology 2009;111:609-15.