Factors complicating interpretation of capnography during advanced life support in cardiac arrest—A clinical retrospective study in 575 patients

doi:10.1016/j.resuscitation.2012.02.021

Resuscitation

Volume 83, Issue 7, July 2012, Pages 813-818

https://doi.org/10.1016/j.resuscitation.2012.02.021 Get rights and content

Abstract

Background

End tidal carbon dioxide (ETCO₂) monitoring during advanced life support (ALS) using capnography, is recommended in the latest international guidelines. However, several factors might complicate capnography interpretation during ALS. How the cause of cardiac arrest, initial rhythm, bystander cardiopulmonary resuscitation (CPR) and time impact on the ETCO₂ values are not completely clear. Thus, we wanted to explore this in out-of-hospital cardiac arrested (OHCA) patients.

Methods

The study was carried out by the Emergency Medical Service of Haukeland University Hospital, Bergen, Norway. All non-traumatic OHCAs treated by our service between January 2004 and December 2009 were included. Capnography was routinely used in the study, and these data were retrospectively reviewed together with Utstein data and other clinical information.

Results

Our service treated 918 OHCA patients, and capnography data were present in 575 patients. Capnography distinguished well between patients with or without return of spontaneous circulation (ROSC) for any initial rhythm and cause of the arrest (p < 0.001). Cardiac arrests with a respiratory cause had significantly higher levels of ETCO₂ compared to primary cardiac causes (p < 0.001). Bystander CPR affected ETCO₂-recordings, and the ETCO₂ levels declined with time.

Conclusions

Capnography is a useful tool to optimise and individualise ALS in cardiac arrested patients. Confounding factors including cause of cardiac arrest, initial rhythm, bystander CPR and time from cardiac arrest until quantitative capnography had an impact on the ETCO₂ values, thereby complicating and limiting prognostic interpretation of capnography during ALS.

Introduction

The partial pressure of end tidal carbon dioxide (ETCO₂) estimates alveolar carbon dioxide (CO₂) tension, and reflects its production, transport to, and elimination from the lungs; hence it generally reflects cardiac output.1, 2 Alteration in one of these factors will affect the measurement. The technique was first described during anaesthesia in the 1950s,³ in order to verify correct tube placement. Monitoring of ETCO₂ during cardiopulmonary resuscitation (CPR) was first described by Kalenda, who used ETCO₂ as a guide to the efficacy of CPR. A drop in ETCO₂ was an indicator for when to change the person providing chest compressions, due to inadequate compression efficacy.⁴ This was later followed by studies reporting its use during CPR in experimental models.1, 5 The positive correlation between ETCO₂ and outcome of cardiac arrest in patients has been well described in several studies,5, 6, 7, 8, 9, 10, 11 and a significant increase in ETCO₂ during CPR has been associated with return of spontaneous circulation (ROSC).12, 13 The 2010 guidelines from European Resuscitation Council (ERC) now encourage the use of capnography to guide CPR during Advanced Life Support (ALS).¹⁴

Interpretation of ETCO₂ during resuscitation from cardiac arrest is still challenging and has several pitfalls. Especially the cause of the arrest seems to have impact on the ETCO₂, and recent studies have described higher ETCO₂ in asphyxial arrests compared with arrests of cardiac aetiology.15, 16 Further, the influence of bystander CPR may impact on ETCO₂ as well as variations over time, but this has not been documented in clinical studies.

Thus, the aims of the study were to document levels of ETCO₂ in patients with out-of-hospital cardiac arrest (OHCA). We hypothesised that although capnography will give valuable feedback to the ALS providers, initial heart rhythm, cause of the arrest, presence of bystander CPR and time dependency will limit and complicate its interpretation.

Section snippets

Ethics

This retrospective study was carried out at the Emergency Medical Service (EMS), Haukeland University Hospital, Norway. The Privacy Protection Supervisor approved the study and the Regional Committees for Medical Research Ethics had no objections. The need of an informed consent from the patients or the families was waived.

Organisation

Our region has a population of approximately 470,000 people (15,000 km²). Since 1988, the Helicopter Emergency Medical Service (HEMS) at Haukeland University Hospital has

Results

A total of 918 patients received ALS after OHCA during the study period. Patient flow chart with included and excluded patients is shown in Fig. 1. Of 724 eligible patients, ETCO₂ recordings were present in 575 (82%) patients who were included in the final study. Patients with ETCO₂ measurements did not differ from the missing/excluded group regarding gender, age, initial heart rhythm, response times or outcome. All baseline characteristics are presented in Table 1. Data only relates to

Discussion

In the present study we have documented that several factors complicate the interpretation of ETCO₂ during ALS. Although ETCO₂ differs well between patients with and without ROSC, there is no clear generalised cut-off value determining whether ROSC will be achieved or not. Several confounding factors such as cause of the arrest, initial rhythm, bystander CPR and changes over time from arrest until ETCO₂ recordings seem to influence this.

Patients with respiratory causes and initial AS had in

Conclusion

Capnography is a useful tool to optimise and individualise ALS in cardiac arrested patients. However, confounding factors including cause of arrest, initial rhythm, bystander CPR and time from cardiac arrest until quantitative capnography had an impact on ETCO₂ values, thereby complicating and limiting prognostic interpretation of capnography during ALS.

Role of the funding source

Bård E. Heradstveit is a fellow research of The Regional Centre for Emergency Medical Research and Development (RAKOS, Stavanger/Norway). The RAKOS had no influence on the topic, study design or interpretation of the data.

Conflict of interest statement

There are no conflicts of interest.

Acknowledgements

The study was supported by a research grant from the Regional Centre for Emergency Medical Research and Development (RAKOS, Stavanger/Norway). MD Ivar Austlid provided supportive information to the registration, and MD Brian Burns made valuable comments to the manuscript.

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Of 518 eligible patients, mean age was 61, 72% were male, 50% had a bystander-witnessed arrest, and 62% had at least one episode of ROSC. The most common arrest etiology was medical (92%). Among all patients, peak E_TCO₂ during resuscitation prior to SOI was 36.8 mmHg (18.6). E_TCO₂ increased in patients who achieved ROSC immediately after SOI (from 38.3 to 47.6 mmHg; +9.3 CI: 6.5, 12.1); patients with sustained ROSC experienced the greatest increase in E_TCO₂ after SOI (from 37.8 to 48.2 mmHg; +10.4 CI: 7.2, 13.6), while E_TCO₂ in patients who did not achieve ROSC after SOI rose (from 36.4 to 37.8 mmHg; +1.4 CI: −0.1, 2.8).
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^☆: A Spanish translated version of the summary of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2012.02.021.

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Clinical paperFactors complicating interpretation of capnography during advanced life support in cardiac arrest—A clinical retrospective study in 575 patients☆

Abstract

Background

Methods

Results

Conclusions

Introduction

Section snippets

Ethics

Organisation

Results

Discussion

Conclusion

Role of the funding source

Conflict of interest statement

Acknowledgements

Resuscitation

Resuscitation

Resuscitation

Resuscitation

Resuscitation

Ann Emerg Med

Resuscitation

Am J Emerg Med

Resuscitation

Am J Emerg Med

Expired carbon dioxide: a noninvasive monitor of cardiopulmonary resuscitation

Circulation

Do changes in end-tidal PCO2 quantitatively reflect changes in cardiac output?

Anesth Analg

Ventilation and end-tidal carbon dioxide tension; a study during routine anaesthesia

Anaesthesia

Prediction of outcome of cardiopulmonary resuscitation from end-tidal carbon dioxide concentration

Crit Care Med

End-tidal carbon dioxide during cardiopulmonary resuscitation in humans presenting mostly with asystole: a predictor of outcome

Crit Care Med

End-tidal carbon dioxide concentration during cardiopulmonary resuscitation

N Engl J Med

Clinical paper
Factors complicating interpretation of capnography during advanced life support in cardiac arrest—A clinical retrospective study in 575 patients☆

Do changes in end-tidal PCO₂ quantitatively reflect changes in cardiac output?