Just the Highlights: Improving Survival in Cardiac Arrest

Brad Salemi, DO, PGY-2
HCA Florida Brandon Emergency Medicine Program
Program Instagram: @brandonhospital_em

McHale and Moore’s review article discusses several ways to improve patient survival during cardiac arrest. This article will review a select few of their recommendations as well as the evidence available to support those recommendations. Specifically, we will look at transesophageal and transthoracic echocardiography, end tidal CO₂ monitoring, and some of the ways to address refractory cardiac arrest. While not an exhaustive review, the aim of this article is to provide more insight into the evidence surrounding these selected topics.

Transesophageal and Transthoracic Echocardiography During Cardiac Arrest

There are many ways ultrasound can be applied during a cardiac arrest. These uses include identifying potentially reversible causes of cardiac arrest, assessing the efficiency of compressions, and helping understand when resuscitative efforts have become futile.¹ Recently, the interest in the use of transesophageal echocardiography during cardiac arrest, called resuscitative TEE, has grown. When comparing transthoracic and transesophageal echocardiography, Fair et al note that TEE has a shorter pause during pulse checks.² Teran et al provide further support for use of TEE over TTE. Including the potential to improve CPR by more accurately characterizing the patient’s anatomy, as well as both a diagnostic and prognostic role for TEE in cardiac arrest.³

A retrospective study was performed by Reardon et al to assess incorporation of a TEE into clinical practice during cardiac arrest. It encompassed 52 emergency medicine physicians, analyzing 552 total scans performed by those physicians. Their analysis showed the physicians involved in their study were able to produce images that were interpretable with a success rate of 99.3%.⁴ Notably, these results were obtained after 4 hours of training. While McHale and Moore do not comment on the implementation of TEE in the emergency department, McGuire and his co-authors provide an outline for its implementation.⁵ This includes acquisition, storage, cleaning, usage protocols, and even discusses some barriers to implementation. Similarly, another paper by Fair et al discusses these barriers. In their discussion, they outline how a multidisciplinary team could be used to ensure proper acquisition and maintenance of these devices.⁶ With the data provided by McHale and Moore, as well as that compiled for this review article, one could argue for expanded use of TEE in cardiac arrest.

End Tidal Carbon Dioxide

End Tidal CO₂ (ETCO2) monitoring has been widely used during cardiac arrest for many years. Its primary function is as a non-invasive way to estimate cardiac output and organ perfusion during cardiac arrest. ETCO₂ can be used as a measure of the effectiveness of CPR performed during resuscitation. McHale and Moore note that ETCO₂ and depth of chest compression are correlated with cardiac output.¹ Further, it is noted that an ETCO₂ greater than 10mmHG is associated with survival to hospital discharge and better neurological outcomes.⁸

But what other information can we extrapolate from ETCO₂ and what confounding factors may affect interpretation of ETCO₂? The prognosis of out of hospital cardiac arrests is poor, and predicting outcomes of cardiac arrest remains difficult. However, ETCO₂ may provide may be used as a prognostic factor in out of hospital cardiac arrest. An ETCO₂  greater than or equal to 14.3mmHg measured after 20 minutes of resuscitation predicted successful ROSC.⁹ This delineation of 20 minutes was used as studies have shown that, for patients who undergo ACLS for greater than 20 minutes, there is a decreased likelihood of ROSC.¹⁰

However, providers should know that interpretation of ETCO₂ can be confounded by several factors. For example, in one study, patients for whom a respiratory cause resulted in cardiac arrest were noted to have significantly higher levels of ETCO₂ on capnography when compared to patients with a cardiac cause of their arrest. This discrepancy could be explained by hypercapnia that was caused by the patient’s respiratory status.¹¹ On balance, animal models have shown that epinephrine can cause a decreased in ETCO₂.^{12, 13} In a study performed by Callaham et al, measurements of ETCO₂ following administration of epinephrine were obtained. While they reported that there was an overall decrease in ETCO₂ following the administration of epinephrine, the patient response was not consistent. They reported that in 33% of patients there was no change, in 28% the level of ETCO₂ increased, and in 33% the ETCO₂ decreased.¹⁴ Bicarbonate, another commonly used medication during resuscitation of cardiac arrest, produced an increase in ETCO₂. While there are factors that may confound values of ETCO₂ obtained during resuscitation of a patient in cardiac arrest, the evidence continues to support its use.

Refractory Cardiac Arrest

Refractory cardiac arrest presents a difficult scenario for a clinician. While there are few therapies for arrests without a shockable rhythm, more options are available when ventricular fibrillation or ventricular tachycardia are the underlying cause. Amiodarone and lidocaine are recommended by current guidelines.¹⁵ However, as McHale and Moore note, despite the widespread use of these drugs, there is little evidence demonstrating their efficacy.^{16, 17} While the evidence for positive outcomes may be lacking, the PROCAMIO trial did show that in the setting of wide complex tachycardia, lidcocaine may be preferrable due to fewer cardiac events following its administration as well as a higher proportion of patients having termination of their tachycardia.¹⁸

Defibrillation is another option for physicians when addressing VF or VT. In scenarios where at three shocks have been performed, consideration of double sequential defibrillation (DSED) or vector change (VC) is reasonable. As in the previous discussion of amiodarone and lidocaine, there is discrepancy among available evidence. McHale and Moore note that in The Double Sequential External Defibrillation for Refractory Ventricular Fibrillation trial, the results showed that survival to hospital discharge was more frequent in patients receiving DSED and VC when compared to standard defibrillation.^1,19 It should be noted that this study was discontinued due to the coronavirus pandemic. The study also noted that the patients receiving DSED had better neurological outcomes.

While these results are promising, there are other studies that do not elicit similar results. A review conducted by Miraglia, et al, which encompassed 1061 patients, noted that more information regarding best practices was needed, as current evidence is insufficient.²⁰ This was echoed in another study performed by Deakin et al, and they further noted that there was no difference in outcomes from out of hospital cardiac arrest when DSED was used.²¹ Clearly, the mixed results from DSED require further inquiry.

The last topic we will look into is the use of extracorporeal membrane oxygen (ECPR) in cardiac arrest. As McHale and Moore note, ECPR is a bridge therapy to definitive treatment.¹ They note in their review that observational studies and two randomized controlled studies showed that ECPR is associated with improved survival in cardiac arrest. In a study performed by Siao et al, conventional resuscitation was compared with resuscitation augmented by ECPR. While the total time of resuscitation was greater in the ECPR group, this group had higher rates of ROSC, and higher survival rate at discharge.²² An observational study that included in-hospital and out-of-hospital cardiac arrests showed that, in both cases, patients in whom ECPR was used had improved survival rates and neurological outcomes at discharge. From this, the authors concluded that outcomes after cardiac arrest could be improved by addressing multiple organ systems.²³ Logistically, use of ECPR poses several problems. Timing of initiation is critical to ensure appropriate use of resources. The cost of attaining adequate resources to perform ECPR, maintaining patients on ECMO, and ensuring providers have adequate training to care for patients may be prohibitively expensive for many hospitals.²⁴

In this article we looked at a select few of the strategies provided by McHale and Moore’s review article. Resuscitative TEE has promising applications, however obtaining and maintaining a TEE may be difficult for some hospitals. ETCO₂ can be affected by a variety of conditions and even some medications provided during cardiac arrest. Providers should take clinical context into account in interpreting ETCO₂ levels. Amiodarone and lidocaine, while currently recommended, have little evidence supporting their efficacy. However, lidocaine may be preferrable in wide complex tachycardia. While there is promising evidence for DSED and VC, more evidence is needed. Finally, ECPR may improve ROSC, but can be prohibitively expensive for hospitals and requires specialized training to ensure proper use.

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