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.

The presence of an enlarged right ventricle (RV) in the patient with PEA can prove difficult to interpret. We recognize that the presence of an enlarged RV may indicate chronic RV disease, lack of forward cardiac flow in cardiac arrest, and other pathologies not from PE. The presence of an enlarged hypodynamic RV in the presence of a hyperdynamic left ventricle may be a more specific finding, but it can be difficult to interpret in the brief interval during active chest compressions.

Overall, we recommend that if signs of right heart strain are present, PE should remain a consideration, and the underlying goal of the active resuscitation should be to attain ROSC, followed by a more detailed POCUS or computed tomography imaging. The decision to administer thrombolytics remains controversial, and current AHA guidelines recommend confirming the diagnosis of PE prior to fibrinolysis.¹⁴

Step 3: Cardiac Activity

The presence or absence of cardiac activity provides useful prognostic information for patients in PEA. Patients in PEA with cardiac standstill on ultrasound have survival to hospital discharge rates ranging from 0.0 to 0.6 percent.⁵ We have intentionally placed the detection of cardiac activity at the end of the CASA exam for two primary reasons. First, as detailed above, there is variability in physician interpretation of cardiac activity.¹⁵ Second, after several rounds of cardiac compressions, a persistent inactive heart will be more clear to the provider, and in conjunction with clinical data (ie, potassium, pH, total down time, and comorbidities) and end-tidal CO₂ readings, determination of when to end resuscitative measures can be more definitive.

Ancillary Steps: Pneumothorax and FAST

Evaluating for pneumothorax and the focused assessment with sonography in trauma (FAST) examination are ancillary steps of the CASA exam because these can occur during any time of the resuscitation and need not occur during a pulse check. Tension pneumothorax is a rare cause of nontraumatic cardiac arrest and can often be diagnosed clinically.¹¹ During ongoing CPR, examine the anterior chest for the absence of lung sliding indicating pneumothorax. If you detect a pneumothorax, consider needle decompression or thoracostomy. Small, clinically insignificant pneumothoraces can occur from rib fractures during CPR, and clinicians should know these injuries may not require acute intervention.

Also, during ongoing CPR, if the clinical scenario indicates, the physician can assess for a ruptured abdominal aortic aneurysm or ectopic pregnancy by performing a FAST exam looking for evidence of free fluid. We intentionally excluded evaluation of the inferior vena cava (IVC) and hypovolemia from the CASA exam because intravenous fluids are traditionally given empirically in cardiac arrest and we expect the IVC to be distended in most cardiac arrests because there is severely limited forward flow.

Summary

POCUS is a powerful tool for assessing reversible causes of cardiac arrest. However, it must be utilized in a protocolized, efficient manner to reduce error and minimize CPR interruptions. The CASA exam provides a framework for clinicians to maintain high-quality CPR while also assessing for the highest-yield reversible causes of PEA that can be visualized with ultrasound.

We hope the integration of a simplified, step-wise exam into the resuscitation of the OHCA patient will limit prolonged CPR pauses while allowing POCUS to improve diagnostic accuracy.

References

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2. Clattenburg EJ, Wroe P, Brown S, et al. Point-of-care ultrasound use in patients with cardiac arrest is associated prolonged cardiopulmonary resuscitation pauses: a prospective cohort study. Resuscitation. 2018;122:65-
3. Huis In ‘t Veld MA, Allison MG, Bostick DS, et al. Ultrasound use during cardiopulmonary resuscitation is associated with delays in chest compressions. Resuscitation. 2017;119:95-98.
4. Gardner KF, Clattenburg EJ, Wroe P, et al. The Cardiac Arrest Sonographic Assessment (CASA) exam – a standardized approach to the use of ultrasound in PEA [published online ahead of print Aug. 26, 2017]. Am J Emerg Med.
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9. Zengin S, Yavuz E, Al B, et al. Benefits of cardiac sonography performed by a non-expert sonographer in patients with non-traumatic cardiopulmonary arrest. Resuscitation. 2016;102:105-109.
10. Breitkreutz R, Price S, Steiger HV, et al. Focused echocardiographic evaluation in life support and peri-resuscitation of emergency patients: a prospective trial. Resuscitation. 2010;81(11):1527-1533.
11. Beun L, Yersin B, Osterwalder J, et al. Pulseless electrical activity cardiac arrest: time to amend the mnemonic “4H&4T”? Swiss Med Wkly. 2015;145:w14178.
12.   Kürkciyan I, Meron G, Sterz F, et al. Pulmonary embolism as a cause of cardiac arrest: presentation and outcome. Arch Intern Med. 2000;160(10):1529-1535.
13. Comess KA, DeRook FA, Russell ML, et al. The incidence of pulmonary embolism in unexplained sudden cardiac arrest with pulseless electrical activity. Am J Med. 2000;109(5):351-356.
14. Jaff MR, McMurtry MS, Archer SL, et al. Management of massive and submassive pulmonary embolism, iliofemoral deep vein thrombosis, and chronic thromboembolic pulmonary hypertension: a scientific statement from the American Heart Association. Circulation. 2011;123(16):1788-1830.
15. Hu K, Gupta N, Teran F, et al. Variability in interpretation of cardiac standstill among physician sonographers. Ann Emerg Med. 2018;71(2):193-198.

Dr. Gardner, Dr. Clattenburg, and Dr. Wroe are emergency medicine residents at Highland Hospital, Alameda Health System, in Oakland, California.

Dr. Nagdev is director of emergency ultrasound at Highland Hospital.