Cardiac arrest (CA) is a sudden loss of blood flow to body organs resulting from cessation of cardiac mechanical activity in a person who may or may not have a diagnosed heart disease. If not treated promptly, it usually leads to death.(1) Symptoms include loss of consciousness and abnormal or absent breathing.(2)
In Europe, out-of-hospital cardiac arrest affects about 55-113 per 100,000 inhabitants a year or 350,000-700,000 individuals a year while the reported incidence of in-hospital cardiac arrest is in the range of 1-5 per 1000 admissions.(3)
Cardiac arrest is an extreme medical emergency and prognosis is generally poor with less than 5% survival rate for those who have out-of-hospital cardiac arrest.(4) Published survival rates from in-hospital cardiac arrest vary substantially and range from 13-59 % at 24 hour and 3-27 % to hospital discharge, with a median survival to discharge of about 15 %.(5)
Cardiac arrest is preceded by no warning symptoms in approximately 50% of people. For those who do, they have non-specific symptoms such as new or worsening chest pain, shortness of breath, fatigue, blackouts, dizziness, weakness, nausea and vomiting.(6)
Recognizing cardiac arrest can be challenging. It is usually diagnosed clinically by the absence of a central pulse. In many cases lack of carotid pulse is the gold standard for diagnosing cardiac arrest as lack of peripheral pulses may result from other conditions (e.g. shock), or simply an error on the part of the rescuer. Nonetheless, studies have shown that rescuers often make a mistake when checking the carotid pulse in an emergency, even if they are healthcare professionals. (7)
Owing to the inaccuracy in this method of diagnosis, some bodies such as the European Resuscitation Council (ERC) have de-emphasized its importance. The Resuscitation Council of the united kingdom (UK), in line with the ERC’s recommendations and those of the American Heart Association (AHA), have suggested that the technique should be used only by healthcare professionals with specific training and expertise, and even then that it should be viewed in conjunction with other indicators such as agonal respiration. (7)
The interventions that contribute to a successful outcome after a cardiac arrest can be conceptulised as a chain – the Chain of Survival Figure (1).(8)
All four links of the Chain of Survival must be strong. They are:
• Early recognition and call for help.
• Early cardiopulmonary resuscitation (CPR).
• Early defibrillation.
• Post-resuscitation care.(8)

Figure (1): Chain of Survival. (8)

Early recognition and call for help:
Out of hospital, early recognition of the importance of cardiac origin of chest pain will enable the victim or a bystander to call the Emergency Medical Services (EMS) so that the victim can receive treatment that may prevent cardiac arrest. After out-of-hospital cardiac arrest, immediate access to the EMS is vital. In most countries access to the EMS is achieved by means of a single telephone number (e.g. 123, 999). (9-11)
Early CPR:
Chest compressions and ventilation of the victim’s lungs will maintain a certain degree of circulation, which may prevent ventricular fibrillation from deteriorating to asystole before EMS arrives. After out-of-hospital cardiac arrest, bystander CPR extends the period for successful resuscitation and at least doubles the chance of survival after ventricular fibrillation (VF) cardiac arrest.(12) Studies show that performing chest-compression-only CPR is better than giving no CPR at all. (13)
Early defibrillation:
After out-of-hospital cardiac arrest, the goal is to deliver a shock (if indicated) within 5 min of the EMS receiving the call as the survival rate of patients receiving their first shock at 5 minutes is twice as high as that of patients treated at 11 minutes. In many areas, achievement of this goal will require the introduction of Public Access Defibrillation (PAD) programs using automated external defibrillators (AEDs).(14)
Post-resuscitation care:
Return of a spontaneous circulation (ROSC) is an important phase in the continuum of resuscitation; however, the ultimate goal is to return the patient to a state of normal cerebral function, a stable cardiac rhythm, and normal hemodynamic function, so that they can leave hospital in reasonable health at minimum risk of a further cardiac arrest. The quality of treatment in the post-resuscitation period influences the patient’s ultimate outcome. The post-resuscitation phase starts at the location where ROSC is achieved. (15)
The Advanced Life Support (ALS) algorithm is the center point of management of cardiac arrest and is applicable to most cardiopulmonary resuscitation situations. Some modifications may be required when managing cardiac arrest in special circumstances such as hypothermia and electrolyte disturbances. Figure (2).(16) ?

Figure (2): Adult advanced life support algorithm.(16)
As previously mentioned, Cardiac arrest patients have a high mortality and few survive to leave the emergency department (ED) alive. So many EDs now have protocols for treating arrest patients as well as cessation of resuscitative efforts. However, for patients who arrive in the ED in cardiac arrest, attempts at resuscitation often continue for prolonged periods of time and utilize considerable resources. Frequently, it is dif?cult to stop resuscitative efforts if electrical activity is still noted on a cardiac monitor or electrocardiogram.(17)
The decision to terminate resuscitation in the setting of cardiac arrest is a difficult one and is based on several factors. Both the American Heart Association and the European Resuscitation Council have published guidelines to assist the clinician with the decision to cease resuscitative efforts, but many of the criteria described are judgment based. Even with such guidance, the emergency physician is often unsure of when to stop resuscitative efforts. Table (I) (18)
Table (I): Guidelines for terminating resuscitative efforts (AHA and ERC).(18)
American Heart Association
• Decision to terminate rests with the team leader based on:
– Time to CPR.
– Time to defibrillation
– Comorbid disease.
– Pre-arrest state.
– Initial arrest rhythm. European Resuscitation Council
• Presence of advanced directive.
• Asystole for more than 20 minutes in the absence of reversible causes.
• Patients with primary out-of-hospital cardiac arrest who require ongoing CPR without return of pulses during transport to the hospital.
• Team leader’s clinical judgment
An accurate method of predicting certain death in the ED would be bene?cial in the decision making in cardiac arrest patients. Resources could be diverted elsewhere and a great deal of effort could potentially be saved. But, the mechanism used to predict no chance for survival should be accurate and highly reproducible. As bedside ultrasonography becomes more widespread in EDs, it is now possible to use real-time cardiac imaging during cardiac arrest. (17)
Emergency ultrasound or point-of-care ultrasound (POCUS) is the application of ultrasound at the point of care to make immediate patient-care decisions. It is performed by the health care professional caring for the injured or ill persons. This point-of-care use of ultrasound is often to evaluate an emergency medical condition in settings such as an emergency department, critical care unit, ambulance, or combat zone.(19-21)
Emergency ultrasound is used to quickly diagnose a limited set of injuries or pathologic conditions,(22) specifically those where conventional diagnostic methods would either take too long or would introduce greater risk to a person (either by transporting the person away from the most closely monitored setting, or exposing them to ionizing radiation and/or intravenous contrast agents). (23)
Point-of-care ultrasound has been used in a wide variety of specialties and has increased in use in the last decade as ultrasound machines have become more compact and portable.(24) It is now used for a variety of exams in various clinical settings at the person’s bedside. In the emergency setting, it is used to guide resuscitation and monitor critically ill persons, provide procedural guidance for improved safety and confirm clinical diagnosis. Point of care ultrasound is sometimes the only option in the evaluation of injured persons who are too ill for transport to other imaging modalities (e.g. computed tomography) or whose illness is so acute that medical decisions in their care need to be made in seconds to minutes. It is also increasingly used to guide and triage care in resource-limited situations, in rural or medically underserved areas.(25)
The main utility of POCUS in CA is suggested in non-shockable rhythms (i.e., pulseless electrical activity (PEA) and asystole), aiming at identifying reversible causes of CA, such as cardiac tamponade, pulmonary embolism, hypovolemia and tension pneumothorax.(26, 27). POCUS-guided pericardiocentesis, needle decompression and fluid challenges can be performed during CPR, many times resulting in ROSC. In this way, POCUS use in CPR can lead to improved management in a significant number of patients. Additionally to rule in or out these four basic reversible causes of CA, other conditions can be diagnosed, such as severe valve problem, severe LV or RV systolic failure and cardiac rupture.(28-30)
Determining a true asystole versus a fine ventricular fibrillation can be made using POCUS, especially when rhythm monitoring is in doubt (e.g., has artifacts), with both prognostic and therapeutic implications, since patients with fine ventricular fibrillation probably benefit from defibrillation and have best chances of ROSC and survival.(31, 32)
True PEA is defined as the clinical absence of ventricular contraction despite the presence of electrical activity, whereas pseudo-PEA is defined as the presence of ventricular contractility visualized on cardiac ultrasound and electrical activity in a patient without palpable pulses. Therefore, making the diagnosis of pseudo-PEA can be of diagnostic and prognostic importance. Patients with pseudo-PEA have some observable, although minimal, cardiac output and have a higher survival rate, in part because there are often identifiable and treatable causes of their arrest.(33) Although there is ample literature to support that causes of PEA and pseudo-PEA can be identified with POCUS, research is now focused on patient outcomes. Identification of causes of PEA arrest by POCUS with zero or minimal interruption in cardiopulmonary resuscitation improves outcomes by decreasing time to treatment and to return of spontaneous circulation.(34)
Several POCUS protocols have been created to be used in the emergency and critically ill patients,(35, 36) although few of them are focused on CPR for the recognition of reversible causes of CA, such as the C.A.U.S.E. (37), FEEL(28), FEER(33), P.E.A. (38) and SESAME protocols (39, 40) . FEEL and FEER explore the heart only, C.A.U.S.E. explores the heart and lung; P.E.A. and SESAME are multi-organ protocols, exploring the heart, lung, abdomen and proximal deep veins of lower limbs. Instead of arguing in favor of or against one protocol over the other, choosing one of them and using it systematically in the emergency department or critical care unit seems to be the best approach. Furthermore, each department can also create its own protocol or algorithm. Table (II) (41)
Table (II): POCUS protocols to be used in CPR. (41)
SESAME (39, 40)
PEA(38) *

Cardiac 1 1 4 2
Lung ultrasound: pneumothorax 2 – 1 1
Proximal DVT (lower extremities) – – 2–3 (first in non-traumatic arrest) 3
Abdomen: e.g., free fluid, ruptured abdominal aorta – – 2–3 (first in traumatic arrest) 3
Numbers refer to the order in which scans are performed.
CAUSE cardiac arrest ultrasound exam, FEEL focused echocardiographic evaluation in life support, FEER focused echocardiographic evaluation in resuscitation, PEA parasternal-Epigastric-Abdomen and other scans (*the order of scans can vary according to clinical setting), SESAME sequential emergency scanning assessing mechanism or origin of shock of indistinct cause, DVT deep venous thrombosis.
Integrating US into CPR should follow one basic premise: POCUS must not interfere with the CPR. Thus, POCUS is safely integrated into the CPR when it is performed in the first rhythm assessment and in the 10 s intervals to check carotid pulse and observe other physiological variables (capnography, invasive arterial pressure) looking for signs of ROSC. Thus, operators should be properly trained in obtaining and interpreting images in these timeframes. The presence of an operator who is exclusively, or at least preferentially, dedicated to ultrasound scanning would be desirable.(34)
Technically, the US machine must have a very rapid boot-up and setup and be rapidly available, as happens with portable equipment. Hand-held devices are also useful for this purpose. Using transducer capable of exploring all areas (e.g. a convex or micro-convex probe) is preferable or eventually two transducers, such as a phased-array probe and a linear probe, as long as rapid switch between them is achievable. (39, 40)
The FEEL protocol is performed by obtaining 4 standard TTE views: parasternal long axis (PLAX), parasternal short axis (PSAX) Apical 4 chamber (A4Ch), and subcostal (SC); which should be synchronized with pulse checks thus limiting no-flow intervals during CPR.
It is used to diagnose potentially treatable causes of cardiac arrest and circulatory collapse:
• Myocardial insufficiency (including acute myocardial infarction).
• Pericardial collection (PC).
• Pulmonary embolism (PE).
• Hypovolemia.(28)
The FEER examination is a ten-step procedure. Its structure is designed to be executed simultaneously during CPR cycles to reduce the unwanted interruptions in chest compressions, the ten steps are:
1) Perform immediate and accurate BLS and ACLS according to AHA or ERC guidelines, at least ?ve cycles of chest compression and ventilation.
2) Tell the CPR team: “I am preparing an echocardiogram”.
3) Prepare portable ultrasound (let prepare) and test it.
4) Accommodate situation (e.g., best position of patient and doctor, removal of clothes), be ready to start.
5) Tell CPR Team to count down 10 seconds and to undertake a pulse check simultaneously.
6) Command: “Interrupt at the end of this cycle for echocardiography”.
7) Put the probe gently onto the patient’s sub-xiphoid region during chest compressions.
8) Perform a subcostal (long axis) echocardiogram as quickly as possible. If you cannot identify the heart after 3 seconds, stop the interruption and repeat again ?ve cycles later and repeat with the parasternal approach.
9) Command after 9 seconds at the latest: “Continue CPR” and control it.
10) Communicate (after continuation of chest compressions only) the ?ndings to the CPR team (e.g. wall motion, heart is squeezing, cardiac standstill, (massive) pericardial effusion, no conclusive ?nding, suspected pulmonary artery embolism, hypovolemia) and explain consequences and follow-up procedure. (33)
C.A.U.S.E. protocol, an acronym for cardiac arrest ultrasound examination, and whose name has the added benefit of reminding the practitioner that the primary goal of their effort in PEA or asystole should be to identify and address the underlying cause.
This protocol addresses four leading causes of cardiac arrest and achieves this by using two sonographic perspectives of the thorax; a four-chamber view of the heart and pericardium and antero-medial views of the lung and pleura at the level of the second intercostal space at the mid-clavicular line bilaterally. The four-chamber view of the heart and pericardium is attained using either the subcostal, parasternal or apical thoracic windows. This allows the individual performing the examination to select the most adequate view depending on the patients’ anatomy. It is recommended to begin with the subcostal view first as this view makes it possible for the practitioner to evaluate the heart without interrupting chest compression.
If this view is not possible then the apical or parasternal approaches may be used during coordinated pulse checks lead by the resuscitation team leader. A four-chamber view is used in this protocol as it allows for ease of comparison between the different chambers in the heart, facilitating the diagnosis of hypovolemia, massive PE, and cardiac tamponade. Pneumothorax is diagnosed by identifying the lack of sliding sign and comet-tail artifact while looking in the sagittal plane at the second intercostal space of the mid-clavicular line. (38)
For both the cardiac and lung views it is recommended to use a 2.5-5.0 phased array transducer probe. This allows the examiner to use the same probe for both lung, heart and if needed abdominal exam. This type of probe was used by Knudtson in his study involving ultrasound for the use of identifying pneumothorax as an addition to the FAST exam, and it yielded a very high accuracy in detecting pneumothorax, yet still remained useful in identifying the heart and abdominal organs.(42)
Pulseless patients are treated with standard resuscitative protocol. After the monitor is attached patients are divided into two groups: arrhythmogenic (i.e. ventricular fibrillation and ventricular tachycardia) and non-arrhythmogenic (i.e. pulseless electrical activity and asystole.) cardiac arrest. Arrhythmogenic patients are treated with electrical defibrillation, but non-arrhythmogenic patients are then examined with the C.A.U.S.E. protocol to exclude readily reversible causes for the cessation of the circulation.
The cardiac view is the first performed as this gives the potential to diagnose one of the three conditions in a single view (massive PE, cardiac tamponade, and hypovolemia), and this view takes the least time, meaning less interference with resuscitation as possible. If the results of the cardiac view are inconclusive the pulmonary views are attempted as these use approximately 30 seconds per side and diagnose only one condition, pneumothorax.(37)
P.E.A. protocol consists of a codified 3 scan sequence of US views in order to recognize underlying reversible causes of CA. The beginning by cardiac imaging, a “black box” in most cases of CA, is recommended for obtaining the most important critical findings on pericardium cavity and myocardial sides and motion (main scans). Then, the other pleuro-pulmonary (complementary scans), thoracic abdominal and peripheral scans (additional scans) are carried on in agreement with the suspected diagnosis based on patient’s history, clinical data and just obtained focused cardiac US findings.
P = Pulmonary scans, for research of pneumothorax, pleural effusion, wet or dry lung;
E = Epigastric and other scans, for research into pericardial effusion, left and right ventricular sides and their wall motion and inferior vena cava (IVC) filling;
A = Abdominal and other scans, for research into thoracic and aortic aneurism and/or dissection, peritoneal effusion, bowel occlusion or perforation, deep venous thrombosis.
The P.E.A. protocol could be performed both during CA in PEA and during peri-arrest conditions, other than after the recovery of a spontaneous rhythm from defibrillation, to check the treatable causes if PEA is not justified by hypoxia or electrolyte abnormalities, toxemia and hypothermia. The sequence of the 3 codified US views in P.E.A. protocol may change based on the patient’s condition.(38)
SESAME-protocol is the abbreviation for “sequential emergency sonography assessing mechanism or origin of severe shock of indistinct cause”. It has been designed for having no button to touch for the first 4 steps (out of 5). The speed is optimized at each level. Traditional echography requires specifically designed probes for each organ. In extreme urgencies, the time it takes to change the probe is a severe issue (in addition to other drawbacks including costs). We use a single probe which is not only perfect for the lung, but also suitable for the whole body. The lung is the most vital organ, but surprisingly, lung ultrasound has been deemed impossible to achieve, based on the wrong belief that ultrasounds cannot traverse air. Studies demonstrated that this dogma was wrong, and that this transparent access to the lung allows to drastically decrease the radiation in many medical fields.(39)
The SESAME-protocol suggests starting with a lung scan to rule out possible causes leading to cardiac arrest. Firstly, pneumothorax needs to be ruled out. Secondly, a partial diagnosis of pulmonary embolism is done following the BLUE-protocol. Thirdly, fluid therapy can be guided, following the FALLS-protocol. The SESAME-protocol continues by scanning the lower femoral veins to check for signs of deep venous thrombosis, followed by (or before, in case of trauma) the abdomen to detect massive bleeding. Next comes the pericardium, to exclude pericardial tamponade. Finally, a transthoracic cardiac ultrasound is performed to check for other (cardiac) causes leading to cardiac arrest.(40)
Cardiac standstill on ultrasonography means absence of any detected ventricular wall motion (VWM) during the period of pulse check which in resuscitation of cardiac arrest patients usually lasts from five to ten seconds. It denotes that the myocardium has expended all of its metabolic resources and mostly would not be recoverable even with the maximum measures of resuscitation. (17)
Bedside ultrasound has been used as an aid in the resuscitation of cardiac arrest patients and it has been noted that patients with cardiac standstill upon arrival in the ED were much less likely to leave the department alive than patients with cardiac contractility, regardless of other modifying factors. Therefore, It has been hypothesized that asystole on echocardiogram signi?es a uniformly poor outcome in ED resuscitations of cardiac arrest patients, regardless of electrical rhythm. (17) So we performed a prospective observational study to evaluate the outcome of patients with echocardiographically con?rmed cardiac standstill.