The goal of this study was to determine how often adequate FOCUS imaging can be obtained in cardiac arrest patients. Among patients presenting to an urban academic medical center over a 6-month period, images were recorded in 92% of cardiac arrest patients, and 84% of those had at least one image rated adequate. This was not significantly different than the number of control patients with at least one adequate image. This study is the first to demonstrate that it is both possible to regularly obtain images during cardiac arrest management and that the adequacy of these images does not differ from those used in non-emergent settings.
Prior studies measuring the efficacy of FOCUS have been performed but have failed to assess a comparable population or used technology that is now considered outdated. Heidenreich et al. were among the first to study this topic and reported that FOCUS provided adequate imaging in only 36% of cases [5]. However, this publication was released in 1995 and ultrasound technology has improved since then. Additionally, their study population consisted primarily of patients experiencing unexplained hypotension rather than cardiac arrest. Using data from the Real-time Evaluation and Assessment Sonography Outcomes Network registry, Gaspari et al. reported that FOCUS was effective in obtaining images that could differentiate between organized and disorganized electrical activity in 76% of patient with a pulseless electrical activity arrest [6]. However, this registry did not include all patients who presented in cardiac arrest during their study period, only those who underwent FOCUS as a part of their resuscitation. Such a convenience sample cannot inform us of how often adequate images can be obtained when FOCUS is deployed routinely. In our study, images were recorded in over 90% of patients, with adequate images obtained in the vast majority of patients. This suggests that FOCUS can be employed routinely by providers treating patients with cardiac arrest.
Ours is the first study to attempt to use a definition for adequate FOCUS imaging during cardiac arrest. We used a definition for adequate based on that developed by Kimura et al. [7]. While this semi-objective scoring system is an improvement compared to an operator’s purely subjective assessment of whether FOCUS images are sufficient, further study is required to link this definition adequate imaging to clinical outcomes and ensure its utility. It is a positive sign that there was a very strong correlation between image interpreters as to the presence or absence of cardiac activity in our study, suggesting the vast majority of studies were likely adequate to answer the study question. Subsequent studies that evaluate for a difference between image quality in FOCUS compared to TEE would do well to incorporate some scoring method, and we feel that the definition of adequacy used in our study would be reasonable.
Multiple studies have shown that FOCUS during cardiac arrest may lead to longer pause times during cardiopulmonary resuscitation compared to when FOCUS is not used [2, 3]. Yet this may be alleviated with role clarity. Pauses are longer when the person leading the resuscitation is also performing the ultrasound [2]. In a prospective study by Lien et al., it was shown that pause duration was almost always < 10 s, the recommended maximum length of a pulse check, when the person performing the ultrasound was an independent member of the team [9]. Pause duration is also shorter when the provider obtaining the FOCUS exam has a higher level of ultrasound training [2]. This suggests that with best practices FOCUS may be used during cardiac arrest without unacceptable pauses.
Some have argued for the use of TEE rather than transthoracic FOCUS in cardiac arrest because TEE images are higher quality [4]. Inherent in this argument is the assumption that regular use of TEE will be as successful as FOCUS in obtaining images. Our study shows that providers can obtain adequate cardiac images in the majority of cardiac arrest cases using FOCUS, while to date there have been no studies that address the ability of the emergency physician to routinely obtain TEE images in consecutive patients. Roadblocks in TEE imaging include the patient having a secure airway, the ability to pass the probe, and the ability to obtain images once the probe is in the correct location. Until a prospective study of TEE on consecutive patients in the ED is performed, recommendations regarding its use should be limited. Ultimately, a randomized trial comparing the two modalities may be necessary.
While TEE images are likely higher quality than FOCUS images, it is uncertain whether higher quality images are required to meet the clinical need in cardiac arrest patients. The main diagnostic goals of echocardiography during cardiac arrest are to identify cardiac activity and to help determine the etiology of the arrest [10]. With limited FOCUS in our study there was agreement on the presence or absence of cardiac activity by both reviewers in 96% of cases, with the only disagreements arising when one reviewer interpreted the study as cardiac standstill and the other as reduced or severely reduced left ventricular function. Thus, a determination on the presence or absence of cardiac standstill may be possible in nearly all patients studied. Although the cardiac arrest patients in our study had significantly fewer views obtained when compared to controls, we suspect that the providers obtained the images needed to make a clinical decision regarding cardiac standstill and concluded the study to move on to other aspects of the resuscitation effort.
Our study has several limitations. It represents a single-center experience. Despite our quality improvement initiative, we were not able to record images in 100% of the cardiac arrests that presented during the study period. Still, images were obtained more frequently than in any previous study, and we believe a sufficient number of patients were included to answer the clinical question [9].
