EtCO2 may not always determine when to terminate resuscitation
Out-of-hospital cardiac arrest (OHCA) is a common occurrence; it’s estimated that approximately 300,000 people per year are treated for OHCA in the United States, with a survival rate of 9.6%.1
EMS systems used to transport all cardiac arrest patients to hospitals, regardless of return of spontaneous circulation (ROSC). However, evidence now suggests that appropriate management of OHCA includes the termination of resuscitation (TOR) in certain settings, given that the overall outcome for many patients is grim.
A 2016 study conducted in Paris, France, indicated that OHCA patients had a survival rate of 0% if the following three criteria were met by the patient: 1) The patient didn’t arrest in front of rescuers; 2) The patient had a non-shockable rhythm; and 3) The patient didn’t respond to two rounds of epinephrine.2
Cardiopulmonary resuscitation (CPR) has evolved substantially since it was first publicly described in 1960. High-quality CPR is critical to the achievement of ROSC.3
Advances in research have addressed many issues in the application of CPR, including:
- The avoidance of over-ventilation;
- Rate of chest compression;
- Use of “compressions-only” CPR early in the course of patient management;
- Depth of compressions; and
- Employment of waveform capnography during the management of the case.
EtCO2 measurement is widely used to determine the effectiveness of resuscitative efforts & to inform the decision to terminate resuscitation during OHCA.
ETCO2 & CPR Effectiveness
Waveform capnography, also known as end-tidal carbon dioxide (EtCO2), is a unique tool for evaluating patient metabolism, circulation and ventilation. EtCO2 levels have been shown to correlate linearly with coronary perfusion pressure and systemic blood flow during CPR.
EtCO2 measurement is widely used to determine the effectiveness of resuscitative efforts and to inform the decision to terminate resuscitation during OHCA.
A rapid rise in EtCO2 during CPR can indicate ROSC due to the improved oxygen delivery to tissues that were compromised during cardiac arrest. A sustained drop or low EtCO2 over time is now understood to be a sign of a futile resuscitation attempt.
A 1997 study published in the New England Journal of Medicine suggested that EtCO2 < 10 mmHg at the 20-minute mark during resuscitative efforts is predictive of the non-survivability of OHCA patients and termination of resuscitation efforts.4
Alternatively, a 2015 meta-analysis of EtCO2 values associated with ROSC during CPR showed that patients with ROSC after CPR have statistically higher levels of EtCO2. In this analysis, the authors found that “the average EtCO2 level of 25 mmHg in patients with ROSC is notably higher than the threshold of 10 to 15 mmHg suggested by the [American Heart Association (AHA)/European Resuscitation Council (ERC)] to improve delivery of compressions and minimize overventilation.”5
The study suggests that EtCO2 goals during resuscitation may be higher than previously believed, and that further studies on clinical targets during resuscitation are necessary to diminish morbidity and mortality after cardiorespiratory arrest.
The clinical guidelines employed in the decision to terminate resuscitation, including duration of resuscitation, cardiac rhythm on the monitor and EtCO2 values obtained by waveform capnography, aren’t standardized among EMS agencies.
A closer examination of these clinical factors in relationship to TOR will be beneficial in for the allocation of appropriate resuscitative efforts. The advantages include the use of EMS resources as well as limiting the emotional trauma to family and bystanders associated with performing and witnessing CPR.
In a study conducted by the authors, the medical directors from the U.S. Metropolitan Municipalities EMS Medical Directors Consortium (the “Eagles” Coalition), which includes some of the largest EMS systems in the world, were surveyed on this issue. The purpose of the study was to elicit the current role of EtCO2 in TOR.
The survey revealed that up to 84% of responding EMS directors found that TOR occurs in patients with EtCO2 values greater than 20 mmHg.
Survey Methods & Results
A five-question poll was sent to medical directors of EMS systems in the Eagles Coalition. The questions were:
- How would you rank, on a scale of 1-10, the importance of EtCO2 in TOR, with 10 being the greatest importance?
- Rank the following in the order of “least” (1) to “greatest” (4) in TOR efforts: Patient-specific factors (e.g., history, age, etc.), ECG rhythm, EtCO2 and duration of resuscitation.
- How often do you find that resuscitative efforts are terminated with EtCO2 > 20 mmHg?
- What factors do you believe may account for any high EtCO2 measurements that may be found in TOR cases (e.g., the administration of sodium bicarbonate, use of an automated compression device, etc.)?
- Has the role of EtCO2 (i.e., importance, reliability) in TOR changed over the past decade? Responses were received from 31 of the EMS medical directors. The first question revealed that the mean impression of the importance of EtCO2 in TOR on a scale of 1 (least importance) to 10 (greatest importance) was 6.77. (See Figure 1.)
Figure 1: Importance of EtCO2 in TOR on a scale of 1 to 10
Figure 2: Average importance of specific clinical factors in TOR
The second question showed that the importance of the listed clinical factors (patient specific factors, ECG rhythm, EtCO2 level and duration of resuscitation) in the decision to terminate resuscitation were all given similar values. (See Figure 2, p. 49.)
The survey revealed that up to 84% of responding EMS directors found TOR occurs in patients with EtCO2 values greater than 20 mmHg. (See Figure 3, p. 49.)
Figure 3: How often are resuscitative efforts terminated with EtCO2 > 20 mmHg?
Based on open-ended responses from question 4, some of the factors that accounted for the higher EtCO2 measurements in TOR cases included:
- Use of automated CPR devices;
- High-quality CPR;
- Underlying respiratory cause for arrest (e.g., massive pulmonary embolism or asphyxia);
- History of CO2 retention at baseline (e.g., chronic obstructive pulmonary disease); and
- Sodium bicarbonate (SB) administration.
Finally, responses to question 5 showed that 85% of those surveyed believe that the role of EtCO2 in TOR decisions has changed over the past decade, and it now plays a more important role than it had in the past. (See Figure 4.)
Figure 4: Has the role of EtCO2 in TOR changed over the past decade?
The results indicate a lack of consensus among survey participants regarding the guidelines used for TOR regarding the use of EtCO2 levels for medical decision-making.
The average importance of EtCO2 in TOR decisions on a scale of 1 (least importance) to 10 (greatest importance) was 6.77, but this value doesn’t reflect a general consensus. Although 71% of participants felt that EtCO2 was important (i.e., rated > 5) in TOR decisions, 29% don’t think that EtCO2 plays an important role (i.e., rated ≤ 5) in the decision to terminate resuscitative efforts.
The second question showed that there’s no real consensus with regard to ranking the importance of the listed clinical factors in the decision to terminate resuscitation.
The survey also revealed that more than 85% of participants believe the role of EtCO2 in TOR has changed in the past decade, and 84% of agencies have terminated resuscitation in cardiac arrests where EtCO2 is > 20 mmHg.
This finding reveals that the threshold of EtCO2 < 10 mmHg at the 20-minute mark of resuscitation as the predictive marker of non-survivability of OHCA, which was set as a result of the 1997 article discussed previously, may need to be re-evaluated.
With improvements in resuscitative methods, there are several potential confounders regarding the increased level of EtCO2 in TOR cases, including higher-quality CPR, use of automated compression devices, underlying respiratory cause for the arrest and the administration of sodium bicarbonate.
It’s interesting to find such a wide variety of opinions among expert EMS medical directors when it comes to determining which clinical factors are most important for TOR. This variability could affect survival, as under- or over-emphasizing specific clinical factors could result in premature termination or inappropriately prolonged resuscitative efforts.
The authors believe that the various factors used in the decision for TOR in the out-of-hospital setting should be standardized for all patients.
The survey results confirm the lack of standardization in guidelines used for TOR and suggest that the use of EtCO2 levels as a guide in determining field TOR may need further examination. Further research may clarify both the role of EtCO2 as well as potential pitfalls of its use in TOR.
1. McNally B, Robb R, Mehta M, et al. Out-of-hospital cardiac arrest surveillance-Cardiac Arrest Registry to Enhance Survival. MMWR Surveill Summ. 2011;60(8):1-19.
2. Jabre P, Bougouin W, Dumas F, et al. Early identification of patients with out-of-hospital cardiac arrest with no chance of survival and consideration for organ donation. Ann Intern Med. 2016;165(11):770-778.
3. Levine R, Wayne M. End-tidal carbon dioxide and outcome of out-of-hospital cardiac arrest. N Engl J Med. 1997;337(5):301-306.
4. Fowler R, Chang M, Idris A. Evolution and revolution in cardiopulmonary resuscitation. Curr Opin Crit Care. 2017;23(3):183-187.
5. Hartmann S, Farris RW, Di Gennaro JL. Systematic review and meta-analysis of end-tidal carbon dioxide values associated with return of spontaneous circulation during cardiopulmonary resuscitation. J Intensive Care Med. 2015;30(7):426-435.