Point-of-care ultrasound (POCUS) is a powerful diagnostic tool in the emergency department. To identify reversible causes of pulseless electrical activity (PEA), emergency physicians have started integrating POCUS into the evaluation of patients in cardiac arrest, leading to its current recommendation from the American Heart Association (AHA).¹

However, two recent studies have demonstrated that ED POCUS use in the resuscitation of out-of-hospital cardiac arrests (OHCAs) may prolong CPR pauses, which has been shown to negatively impact survival.^2,3 In our experience, even experienced ED sonographers can have difficulty simultaneously obtaining adequate echocardiographic views and interpreting their images in the 10-second CPR pause interval, leading to unintended prolonged CPR pauses.

Protocol = Solution

A potential solution for minimizing CPR interruptions may be to protocolize POCUS integration in the resuscitation of the OHCA patient. Prior protocols have been suggested, but they are too complex and can reduce the possibility of clinical implementation. A simplified protocol most ED sonographers can easily perform may reduce the cognitive load of running a complex resuscitation, facilitate detection of reversible causes of OHCA, and prevent prolonged CPR pauses.

The CASA Exam

Recently, we proposed the Cardiac Arrest Sonographic Assessment (CASA) exam (see Figure 1).⁴ The CASA exam is a three-step protocol that evaluates for:

• Pericardial effusion
• Right heart strain indicative of a pulmonary embolus
• Cardiac activity

All three steps can be rapidly performed with a cardiac (phased array) transducer.

Tamponade and pulmonary embolism (PE) are potentially reversible causes if identified quickly, and the presence or absence of cardiac activity provides information regarding prognosis.⁵ This step-wise approach allows for the integration of POCUS in the resuscitation of the critically ill patient while maintaining the evidence-based principles of continuous, high-quality CPR. If and when return of spontaneous circulation (ROSC) is achieved, a more comprehensive ultrasound assessment should be performed.

Probe and Views

We recommend using a phased array transducer with cardiac presets for the echocardiographic examination, and all images should be recorded for review. Our initial cardiac evaluation often utilizes the subxiphoid view because cardiac compressions make the anterior chest difficult to access. The parasternal long axis, our preferred view in patients not in cardiac arrest, can also be used, but the ED sonographer must be resolute in wiping gel from the chest after each echocardiographic evaluation. Leaving gel on the chest will interfere with cardiac compressions and adhesion of the defibrillation pads.

The optimal view of the heart will be based on the patient’s intrinsic pathology. Patients with chronic lung pathology (eg, chronic obstructive pulmonary disease) are often best imaged from the subxiphoid view, but the cardiac location can vary significantly. We recommend obtaining only one view per pause.

Step 1: Pericardial Effusion

Determining the presence of a pericardial effusion causing cardiac tamponade is the first step in the CASA exam because this is the cause of cardiac arrest in 4 to 15 percent of patients.^5-9 The rapid identification of cardiac tamponade is critical because an emergent pericardiocentesis may resolve PEA. Patients with cardiac tamponade as a cause of PEA have a significantly higher survival to hospital discharge rate (15.4 percent) than other PEA causes (1.3 percent).⁵ Unfortunately, cardiac tamponade can be a complex echocardiographic diagnosis, and often subtle signs cannot be determined during the initial resuscitation. The decision to perform an urgent landmark or ultrasound-based pericardiocentesis should be based on both the clinical scenario and ultrasonographic findings.

Step 2: Right Heart Strain

Evaluating for right heart strain indicative of PE is the second step of the CASA exam because this may be the underlying etiology of 4.0 to 7.6 percent of cardiac arrests.^10-13 Furthermore, cardiac arrest patients with PE have significantly better outcomes when appropriate treatment is initiated compared with other etiologies.