Point-of Care Ultrasound in Cardiac Arrest: A Focused Review

Abstract

Cardiac arrest is a common condition with low survival rates. Point-of-care ultrasound (POCUS) has been increasingly integrated in cardiac arrest care to enhance diagnostic accuracy and guide interventions. POCUS can be divided into cardiac and non-cardiac applications. Cardiac applications include assessment of cardiac tamponade, pulmonary embolism, ventricular fibrillation, and chest compression quality. Non-cardiac applications include endotracheal tube confirmation, pneumothorax assessment, and evaluation of aortic and intra-abdominal pathology. POCUS can also be used to identify the presence or absence of a pulse more rapidly and accurately than manual palpation. Prognostic utility is highest in traumatic arrests, but more limited in non-traumatic arrests. In appropriately trained individuals, POCUS is a valuable component of cardiac arrest care.

Introduction

Cardiac arrest is a common condition that presents to the acute care setting, with substantial morbidity and mortality. Globally, the incidence of return of spontaneous circulation (ROSC) is 29.7%, while survival to hospital discharge is only 8.8%. 1 Core tenets of cardiac arrest management include high-quality chest compressions and early defibrillation. 2 However, beyond these core elements, tailored therapy based upon the underlying etiology can be beneficial. One study found a significant increase in both survival to admission and survival to hospital discharge among patients in whom the etiology was identified by the cardiac arrest team. 3

Point-of-care ultrasound (POCUS) is a well-established tool to facilitate rapid diagnoses at the bedside, and this role has increasingly expanded to the evaluation and management of cardiac arrest. 4 , 5 However, there have been concerns regarding the potential to prolong pauses between chest compressions with indiscriminate use. 6 , 7 Therefore, it is important to understand the current evidence and optimal role of POCUS in cardiac arrest. This review will summarize current applications of POCUS in cardiac arrest.

Cardiac Applications

The use of POCUS can be divided into cardiac and non-cardiac applications ( Table 1 ). Cardiac applications focus on directly visualizing the heart with POCUS, whereas non-cardiac applications include those assessments involving other regions of the body (e.g., airway, lungs, abdomen, extremities). When performing cardiac POCUS, it is important to avoid prolonged pauses between chest compressions. Table 2 provides a list of strategies to minimize interruptions in chest compression.

Table 1 . Point-of-care ultrasound (POCUS) applications in cardiac arrest .

DVT: deep venous thrombosis; FAST: focused assessment with sonography in trauma; PE: pulmonary embolism.

POCUS Examination	Pathology Assessed
Cardiac	Cardiac tamponade, right heart strain (massive PE), ventricular fibrillation, hypovolemia, chest compression location, cardiac activity
Airway	Endotracheal tube location
Lung	Pneumothorax, single lung intubation
Abdomen/FAST	Free fluid (e.g., trauma, ruptured ectopic pregnancy), abdominal aortic aneurysm, aortic dissection
Extremity	DVT, POCUS Pulse Check

Table 2 . Strategies to minimize the duration of pauses in chest compressions .

Adapted from Gottlieb and Alerhand 4

1. Have the most experienced sonographer perform the ultrasound. 2. When possible, someone other than the team leader should perform the ultrasound. 3. Place the ultrasound probe on the chest to identify the optimal cardiac window prior to pausing compressions. 4. Record the clip during the pause and wait to analyze the clip until compressions have resumed. 5. Have a designated person count down the time to 10 seconds. 6. Keep a towel nearby to wipe off the ultrasound gel immediately after the ultrasound. 7. Perform the non-cardiac applications (e.g., airway, lung, deep venous thrombosis) while compressions are ongoing.

For cardiac POCUS, there are four main applications: cardiac tamponade, pulmonary embolism, ventricular fibrillation, and chest compression quality. The role of cardiac POCUS for prognostication will be discussed in a subsequent section.

Cardiac Tamponade

Two large studies using POCUS in cardiac arrest have reported that cardiac tamponade may be present in up to 4% of cardiac arrests ( Fig. 1 , Video 1). 8 , 9 Research has demonstrated that emergency physicians are 88%–96% sensitive and 98% specific for identifying a pericardial effusion, including in cases of cardiac arrest. 10 - 12 In the non-cardiac arrest setting, commonly assessed findings of tamponade include right atrial collapse, right ventricular collapse, and sonographic pulsus paradoxus. 13 , 14 However, the absence of normal forward flow can make many of these findings less reliable in cardiac arrest. 4 Given that cardiac tamponade can develop even from small effusions with rapid accumulation, 15 , 16 there is no specific size threshold to exclude tamponade in cardiac arrest. Moreover, one study reported that, among patients in cardiac arrest who underwent a pericardiocentesis for suspected cardiac tamponade, there was a 15-fold higher survival to discharge compared with all other patients. 8 Therefore, it is reasonable to perform pericardiocentesis in patients with a non-trivial pericardial effusion, in whom cardiac tamponade is suspected.

Fig. 1 . Pericardial effusion in a patient with cardiac tamponade. (Extracted from Video 1.) .

Video 1. Available at: https://drive.google.com/file/d/1t2uEV_z2MEIfiKFGDxserYUCIlsMyfkA/view?usp=sharing

Pulmonary Embolism

Pulmonary embolism (PE) may be the underlying etiology for 2%–5% of cardiac arrests ( Fig. 2 , Video 2). 8 , 17 There are numerous echocardiographic findings of acute PE, primarily relying on a combination of right ventricular size, systolic function, and Doppler measures of blood flow. 18 The short interval for performing cardiac assessments during pauses coupled with absent or minimal cardiac activity has prompted many to focus on visual assessment of right ventricular chamber size as the primary predictor of PE. Data suggest that right ventricular dilation is 91% specific for acute PE when performed by physicians. 19 However, this finding is most suggestive of PE early in the cardiac arrest period, as experimental models have demonstrated that the likelihood of right ventricular dilation increases over time, even in the absence of PE. 20 , 21 Based upon this literature, the ideal time to assess for right ventricular dysfunction is within the first six minutes of cardiac arrest. 20 , 21 In addition, one should note that chronic pulmonary hypertension can also lead to right ventricular dysfunction and limit the diagnostic accuracy for PE. To assess for right ventricular hypertrophy from chronic pulmonary hypertension, the right ventricular free wall should be measured in diastole. This is best assessed using the subxiphoid view and measuring on a stored clip. A right ventricular free wall thickness > 5 mm is suggestive of right ventricular hypertrophy. 18 , 22 Therefore, when considering PE, the right ventricular assessment should be performed early and the right ventricular free wall assessed visually or measured for evidence of chronic hypertrophy. When this is not possible or may be delayed, assessment of the lower extremities for deep venous thrombosis is reasonable. 4

Fig. 2 . Dilated right ventricle in a patient with a pulmonary embolism. (Extracted from Video 2.) .

Video 2. Available at: https://drive.google.com/file/d/1t2uEV_z2MEIfiKFGDxserYUCIlsMyfkA/view?usp=sharing

Ventricular Fibrillation

Ventricular fibrillation (VF) is one of the most important causes of cardiac arrest to identify, as it is both reversible with defibrillation and time-sensitive. One study reported a 95% success rate when VF was defibrillated in the first two minutes, with a 6% reduction in success with each additional minute of delay. 23 While traditionally assessed via the cardiac monitor, subtle VF can be missed, particularly in patients with increased soft tissue between the external cardiac pads and heart. A secondary analysis of a study of POCUS in cardiac arrest reported that 8 out of 32 (25%) of patients with asystole or pulseless electrical activity (PEA) on the cardiac monitor had VF present on cardiac POCUS. 24 Another study of 23 patients receiving transesophageal echocardiography (TEE) in the emergency department reported that 4 patients (17%) of those with asystole on the monitor had VF on TEE. 25 While outcome data are currently limited, a separate study of 4 patients with asystole on the monitor but VF on POCUS performed defibrillation for all 4 patients with 100% achieving ROSC. 26 Based upon these findings, POCUS should be used to assess for VF and it is reasonable to perform defibrillation if VF is present.

Quality of Chest Compressions

High-quality chest compressions are a critical element of cardiopulmonary resuscitation. Traditionally, chest compressions have been performed over the center of the chest based on the presumed location of the heart. However, internal anatomy can vary, leading to the area of maximal compression (AMC) occurring in an incorrect location. The ideal AMC location should center on the left ventricular cavity, allowing blood to exit the left ventricular outflow tract (LVOT) to the brain and body. In contrast, if the AMC is instead centered on the LVOT, it can prevent forward flow of blood. One study of 19 patients with cardiac arrest reported that all patients where the LVOT was open (i.e., non-compressed) had ROSC, whereas no patient with LVOT compression had ROSC. 27 Radiologic studies have reported that the aortic root, ascending aorta, or LVOT were located below the traditional location for compressions in 48%–79% of cases. 28 , 29 This is consistent with TEE data of patients in cardiac arrest, with one study reporting the AMC involved the aorta in 59% of cases, while the remainder involved at least partial compression of the LVOT. 30 Another study of TEE reported 53% had compression of the LVOT, with all requiring hand repositioning to improve the cardiac compressions. 25 Therefore, when TEE is available, clinicians should assess for the AMC and reposition the hands of the person performing the compressions if the LVOT is compressed.

Non-Cardiac Applications

Non-cardiac applications include endotracheal tube (ETT) confirmation, pneumothorax, and intra-abdominal pathology. These applications also have the benefit of being able to be performed during compressions, thereby not influencing chest compression pause time.

ETT Confirmation

While end-tidal capnography has excellent accuracy for confirming ETT correct placement in the non-arrest patient, studies have reported the sensitivity may be only 65%–69% in cardiac arrest due to reduced cardiac output and pulmonary blood flow. 31 - 35 In contrast, POCUS is 99% sensitive and 97% specific for identifying endotracheal intubation, with consistent diagnostic accuracy in both the arrest and non-arrest setting ( Fig. 3 ). 36 The accuracy also remains consistent regardless of transducer choice, sonographic technique, or ETT size. 36 - 42 POCUS can also be performed rapidly and does not require positive pressure ventilations, which can increase the risk of gastric insufflation and aspiration. 43 , 44 As the ETT can be dislodged during transport or as a result of cardiopulmonary resuscitation and chest radiographs are generally delayed until post-ROSC, POCUS can also be an invaluable tool for determining ETT depth to avoid single lung intubation. To assess this, the ultrasound transducer can be placed in the sagittal plane at the suprasternal notch to directly visualize the ETT cuff or indirectly assess ETT depth via bilateral lung sliding. 45 - 51

Fig. 3 . (A) Endotracheal intubation; (B) Esophageal intubation.

Pneumothorax

In the supine patient, POCUS in the non-arrest setting has been shown to be 91% sensitive and 99% specific for identifying the presence of a pneumothorax. 52 However, one study suggested a single view at the third intercostal space in the midclavicular line on each side is likely sufficient to identify a clinically significant pneumothorax. 53 Lung sliding is often assessed with B-mode, visualizing for the presence of movement at the visceral-parietal pleural interface. One study suggested adding M-mode to B-mode increased the accuracy for detecting pneumothorax from 89.6% to 94.6% when compared to B-mode alone, with the most pronounced impact seen among more novice users ( Fig. 4 , Video 3). 54 As mainstem intubation can mimic a pneumothorax, it can be beneficial to assess for the presence of a lung pulse, which appears as rhythmic pulsations on M-mode only seen in mainstem intubation. 55 - 58 If a pneumothorax is present, POCUS can also be used to measure the depth to the pleural line to identify the identify the ideal location and ensure needle length is sufficient if a needle thoracostomy is to be performed. 59 , 60

Fig. 4 . (A) Normal lung using M-mode; (B) Pneumothorax on M-mode. (Exacted from Video 3.) .

Video 3. Available at: https://drive.google.com/file/d/1Pcd3sFeEgQwdZ4Nu5wWDOySdFTflgToG/view?usp=sharing

Aortic and Intra-Abdominal Pathology

POCUS can be used to assess for aortic and intra-abdominal pathology to inform surgical planning if ROSC is achieved or to guide decisions about holding thrombolytics and other interventions. POCUS is 98.3% sensitive and 99.8% specific for identifying abdominal aortic aneurysm in non-arrest patients. 61 Evaluating the aortic lumen for a linear flap can also suggest dissection, though it is advisable to visualize this in two planes to avoid misdiagnosing artifact. The focused assessment with sonography in trauma (FAST) can be beneficial to assess for free fluid. In a female patient of child-bearing age, free fluid on the FAST examination may suggest a ruptured ectopic. 62 Similarly, in a patient with preceding trauma, free fluid may suggest organ injury. 63 However, it is important to note that not all free fluid is blood and to exercise caution in patients with alternate etiologies (e.g., ascites, cirrhosis, peritoneal dialysis).

POCUS Pulse Check

Manual pulse checks during cardiac arrest have suboptimal accuracy and can require prolonged time to adequately assess pulses. One study of patients on cardiopulmonary bypass among 206 paramedics and emergency medicine technicians reported 90% sensitivity and 55% specificity for identifying the presence of a pulse by palpation alone. 64 Moreover, only 16.5% of participants could adequately assess the pulse within 10 seconds. 64 In contrast, POCUS can rapidly assess the presence or absence of a pulse by visualizing the carotid or femoral artery with a linear probe and assessing with B-mode or color Doppler ( Fig. 5 , Video 4). Several studies have demonstrated that POCUS is faster and more accurate than manual palpation. 65 - 69 One study compared POCUS with manual palpation among 568 pulse measurements in cardiac arrest and found POCUS was 100% sensitive and 98% specific for predicting ROSC, whereas manual palpation was 80% sensitive and 91% specific. 68 Another group proposed measuring the peak systolic velocity (PSV) using pulsed-wave Doppler and found that if the PSV is ≥ 20 cm/s, POCUS was 91.4% accurate for predicting a systolic blood pressure ≥ 60 mmHg. 69

Fig. 5 . POCUS pulse check. (Exacted from Video 3.) .

Video 4. Available at: https://drive.google.com/file/d/1B0jGt6Dehe1BowwZvQnU7Yk0B2o69zyx/view?usp=sharing

Prognosis

POCUS has been proposed as a prognostic tool to predict ROSC in cardiac arrest. In trauma patients, one large meta-analysis reported POCUS is 91% sensitive and 98% specific for predicting failure of ROSC. 70 Another study evaluated 170 trauma patients (32% cardiac activity) who received a resuscitative thoracotomy (RT) and found that none of the patients who had absent cardiac activity and received a RT survived. Given the time- and resource-intensive nature of RT coupled with potential harm to the clinicians performing it, this data suggests it may be reasonable to not pursue RT in traumatic arrest when cardiac activity is absent. In non-traumatic arrests, POCUS is 92% sensitive and 60% specific for predicting failure of ROSC, suggesting a more limited role in the non-traumatic arrest patient. 71 Importantly, studies have reported moderate agreement in identifying cardiac contractility. 72 , 73 While valve fluttering is commonly present due to positive pressure ventilations and intravenous fluid administration, cardiac contractility should involve coordinated motion of the left ventricular walls. Therefore, clinicians should focus on myocardial movement to avoid misdiagnosing valve motion as true contractility.

Conclusion

In summary, POCUS is a valuable tool for identifying the etiology and guiding interventions in cardiac arrest. However, clinicians should use proper technique to minimize delays in chest compressions. Common cardiac applications include pericardial tamponade, PE, and VF, while non-cardiac applications include ETT confirmation, pneumothorax assessment, and evaluation of intra-abdominal pathology. POCUS is faster and more accurate than manual palpation for pulse check. Prognosis is more accurate in traumatic arrest and can guide the decision for RT, whereas the specificity is lower in non-traumatic arrest. In appropriately-trained hands, POCUS can be an important aspect of cardiac arrest care, allowing for rapid and tailored interventions at the bedside.