The Approach to Out-of-Hospital Cardiac Arrest: Activate an Emergency Response Team and Begin CPR

Every year, over 380,000 Americans die of coronary heart disease.¹ Heart disease is the leading cause of death in the United States.² Cardiac arrest is the secession of effective pump mechanism of the heart, which may manifest as sudden collapse or loss of consciousness. In most cases, cardiac arrest is a direct complication of heart disease. 

Out-of-hospital cardiac arrest (OHCA) is defined as the “cessation of cardiac mechanical activity confirmed by the absence of a detectable pulse, unresponsiveness, and apnea (or agonal respirations).”³ In practical terms, cardiac arrest is the failure of the pumping mechanism of the heart to generate sufficient pressure for the perfusion of vital organs. The organs most susceptible to decreased perfusion include the heart and brain. Decreased perfusion to these organs may results in shortness of breath, chest pain or tightness, and altered level of consciousness. Complete or near complete cession of perfusion to the brain leads to unconsciousness within seconds. The Utstein Symposium³ in 1990 outlined a uniform set of variables and reporting formats for cardiac arrest, which would allow for results to be compared among different hospitals and emergency medical services (EMS) systems.
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There were an estimated 359,400 incidences of OHCA in 2012.¹ There may be few or no warning signs that a victim is about to suffer cardiac arrest. Survival from OHCA is typically low and is largely impacted by location of the arrest event.⁴ Despite advances in cardiac resuscitation, there has been little improvement in the rate of survival from OHCA during the last 30 years.³ 

The chain of survival has been proposed as a series of events that should occur rapidly in order to maximize the chance of resuscitation.⁵ The first 3 links in the chain are:

•Early notification of emergency response agencies (ie, local fire rescue personnel and related public safety resources)

•Bystander cardiopulmonary resuscitation (CPR)

•Early defibrillation

These initial events may all occur before emergency response personnel arrive. There are interventions available to the general public that can increase the possibility that these initial steps in administering care occur with minimal delays. They include public awareness, formal CPR training programs, and deployment of automatic external defibrillators (AEDs). Organizations may even choose to purchase AEDs and develop a public access defibrillation program—to make AEDs available in specific locations for use by the general public. 

This article provides an overview and scientific basis for interventions that can increase survival rates and can be used as a starting point for organizations interested in improving their OHCA preparedness. 

Activating EMS 

In 1991, the American Heart Association (AHA) introduced the concept of chain of survival—a sequence of events that should be executed in the shortest possible time in order to maximize survival from OHCA. The original chain of survival consisted of early access, early CPR, early defibrillation, and early advanced care. Recently, the AHA has added integrated post-cardiac arrest care as well.⁶ 

Early access refers to the activation of EMS, and includes the time necessary for a witness to recognize a potential cardiac arrest, decide to call for help, locate a telephone, place the call, answer triage questions by the emergency medical dispatch (EMD), and for the EMD to contact appropriate emergency personnel.⁵

Note: Cardiac arrest should be assumed in any situation in which a person is seen to collapse or is found unconscious. Cardiac arrest is commonly caused by insufficient blood supply to the heart, or myocardial ischemia. Victims may have symptoms of cardiac ischemia prior to cardiac arrest, which include:⁷

•Uncomfortable pressure, squeezing, fullness, or pain in the center of the chest. It lasts more than a few minutes, or goes away and comes back

•Pain or discomfort in 1 or both arms, back, neck, jaw, or stomach

•Shortness of breath with or without chest discomfort

•Breaking out in a cold sweat, nausea, or lightheadedness 

Identification of cardiac arrest may not be harder as other conditions—eg, intoxication, hypoglycemia, syncope, and postictal state (post-seizure) are other potential causes for a victim to be unresponsive.⁸ Furthermore, approximately half of OHCA patients may exhibit agonal breathing (ie, gasping breaths during cardiac arrest).⁹ Any person that is seen to collapse or is found unarousable should receive an evaluation by a medical professional.¹⁰

In most places within the United States, dialing 911 reaches emergency personnel. In some situations, organizations may have a local emergency response and/or facilities that require specific numbers to be dialed first to assess an outside telephone line. The Federal Communications Commission requires that wireless carriers identify the location of any caller to 911 and route their call to a local public safety answering point, regardless of whether the cellphone is subscribed to the carrier’s service.¹¹ 

The emergency operator will prompt the caller for location and pertinent information in order to appropriately triage the emergency. Protocol-driven questions are used to assess the nature and severity of the emergency; this includes what events led to call for assistance, any known demographics or past medical history for the victim, available resources at the scene, and caller information.¹² Most regions have a tiered response to medical emergencies, with the main branch point being the necessity of advanced life support (ALS) or basic life support (BLS) trained medical transport personnel. Specific criteria have been developed to assist emergency dispatchers in appropriately allocate resources.¹³

Note: Increasing the number of ambulances may not significantly decrease the response time. One model found that the response time decreased with the square root of the number of ambulances per square mile—or 80% more emergency vehicles would be needed to decrease response time by 1 minute.⁵

Impact of Early Activation 

Survival from OHCA is inversely correlated with the amount of time that passed between cardiac arrest and EMS arrival.^14,15 In a retrospective study examining OHCA mortality rates 1-month post-cardiac in Sweden, 9340 patients who collapsed from presumed cardiac etiology and underwent CPR were analyzed.¹⁶ When the time from collapse to call for assistance was ≤4 minutes, survival at 1 month was 6.9%. In comparison, survival was significantly lower at 2.8% (P<0.001) when time to initial call was >4 minutes. For delays between 2 to 8 minutes, overall survival decreased by more than 1% for each additional minute of delay. Researchers noted that delays from collapse to call for EMS (median=4 minutes) accounted for an average of 40% of the entire time from collapse to EMS arrival.

A study reviewing Michigan 911 data and the responses of 688 bystanders found that 48% of cases reported delays (length was not specified).¹⁰ Calls were categorized as delayed if the witnesses estimated that the delay was >4 minutes or there was an intervening event between finding the victim and calling 911. Other reasons for delays included calling a friend/neighbor/physician before EMS, trying to comfort the victim, thinking the victim had suffered a “fainting” spell, and beginning CPR prior to calling EMS. There was a lower likelihood of delay in cases of witnessed arrest or arrest in public locations. In the subgroup of patients with witnessed arrests, survival was decreased substantially (4.6% vs 11.8%) if there was a delay calling 911. 

A study based on EMS data in the Pittsburgh area showed that survival decreased as the length of time it took for ACLS trained personnel to arrive increased.¹⁴ Victims of OHCA were separated in 3 groups based on delay: <5 minutes, 5 to 15 minutes, and >15 minutes. Survival to hospital discharge decreased when comparing groups with longer response times—24.0% for <5 min, 12.7% for 5 to 15 minutes, and 7.0% for >15 minutes. When the same data was categorized into survivors and nonsurvivors, the group of survivors reported a 7.29 minute delay to ACLS arrival versus 9.49 minute for nonsurvivors.

When EMS personnel are dispatched to treat symptoms of cardiac ischemia prior to cardiac arrest, survival rates improve. Researchers looking at data published from King’s Daughters Medical Center in 2010¹⁵ classified cardiac arrest incidents as unwitnessed (survival rate of 4.7%), witnessed by a bystander (survival rate of 26%), or witnessed by EMS (survival rate of 35%). A Japanese study collaborated these results by analyzing 1-year survival rates for witnessed (3%) versus unwitnessed (0.7%). 

One study found that almost 75% of cardiac arrests in the United States occur at home; at-home arrest survival rates were at 6% compared to 17% at public locations.¹⁷ When an arrest occurred at home, there was a much lower (36% vs 55%) probability that the arrest would be witnessed. Data also confirms a 3% survival if the cardiac arrest was witnessed versus 0.7% if unwitnessed.¹⁷

Administering CPR

CPR is a combination of artificial respiration and external chest compressions intended to maintain perfusion and oxygenation to victims of cardiac arrest. Chest compressions provide a mechanical pumping action that circulates the blood. Artificial respirations provide oxygenated air to the lungs where oxygen can diffuse into the blood. CPR is not intended restart the heart, but to temporarily assist until definitive treatment (eg, cardiac defibrillation or ALS medications) can be provided. 

The methods for external chest compressions and mouth-to-mouth respirations were developed in the 1950s. James Elam, an anesthesiologist, was the first to determine that exhaled air contained enough oxygen to sustain a human.¹⁸ He performed several experiments showing the effectiveness of mouth-to-mouth respirations on anesthetized subjects.¹⁹ Around the same time, researchers from Johns Hopkins University discovered methods for closed chest cardiac massage; they found that forceful pressure with the defibrillator paddles could create a femoral artery pressure pulse.²⁰ 

The combination of artificial respiration and chest compressions is now referred to as BLS. In 1963, the AHA first endorsed CPR and has since incorporated BLS curriculum and dissemination of CPR training into their mission. A 2008 AHA survey reported that 60% of the general public are familiar with CPR.²¹ The AHA currently recommends that all high school students receive CPR training and BLS has become part of the mandatory curriculum for secondary schools in many states.²²

(The Impact of CPR on next page)

The Impact of CPR 

The current rate of survival to hospital discharge for a victim of OHCA is very low and has changed little over the last 30 years.⁴ An estimated 166,000 people suffer from OHCA in the United States every year. In a large meta-analysis including over 143,000 victims of OHCA, survival to hospital admission was found to be 23.8% and survival to hospital discharge was 7.6%.⁴ Of note, a study examining the impact of CPR found that resuscitation is successful in over 50% of cases involving the general public.²³ 

CPR has been shown in numerous studies as having a substantial impact on survival from OHCA.^4,24,25 A study intended to determine the effectiveness of rapid defibrillation and ALS measures (eg, intubation and intravenous drug administration) found that overall survival to hospital discharge with ALS interventions by trained paramedics was 5.1% as compared to 10.5% when bystander CPR was performed.²⁴ 

A 2010 meta-analysis pooled data from 79 studies and 142,740 patients to determine factors associated with survival from OHCA.⁴ Several factors were associated with survival, including witnessed arrest and initial cardiac rhythm of ventricular tachycardia or ventricular fibrillation. Of these, 32 studies, accounting for 76,485 participants, included explicit data regarding whether bystander CPR was performed. The data showed that bystander CPR was associated with an odd ratio of 2.44 favoring survival. 

The AHA now endorses the use of dispatcher-assisted CPR.^26-28 In dispatcher-assisted CPR, the EMD asks the bystander if the victim is responsive and breathing normally. If the victim is not responsive and not breathing normally, it is assumed the victim is in cardiac arrest, at which point easy-to-follow instructions for performing CPR are given.²⁹ 

To compare dispatcher-assisted CPR to no instruction, 655 studies between 1985 and 2009 were reviewed and 5 were found to meet the criteria. These studies were all either observation or retrospective cohort studies and 1 showed statistically significant improvement in mortality. In the remaining 4 studies, 3 showed a trend towards improved outcome that did not reach statistical significance. One study showed a trend towards decreased survival. 

In 2010, the New England Journal of Medicine published 2 randomized, controlled trials comparing traditional CPR (chest compressions and mouth-to-mouth ventilation) with chest compressions-only CPR.^27,28 The primary outcome of this study was survival to hospital discharge. There was no statistically significant difference in survival to hospital discharge between the group receiving compression-only CPR and the group receiving traditional CPR.
However, the group receiving compression-only CPR had a trend toward better outcomes. 

Another study determined the impact of performing CPR with or without ventilations on patients with OHCA, with a primary end point of 30-day survival. The results showed no statistically significant difference in survival at 30 days between the group of patients receiving CPR with ventilation and patients receiving compression-only CPR. However, there was a trend toward improved survival in the compression-only CPR group. 

Based on this emerging data, the AHA’s latest CPR guidelines focus on high quality chest compressions.³⁰ The AHA has rearranged the order of priority from A-B-C (airway, breathing, chest compressions) to C-A-B (chest compressions, airway, breathing) in order to decrease the amount of time it takes to begin chest compression.³⁰ Note: The “look, listen, and feel” action steps to determine if a patient is breathing or has a pulse were also removed from the initial assessment. It is now recommended that any person who is found to be unresponsive and is not breathing normally should be assumed to be in cardiac arrest. 

Untrained rescuers are encouraged to perform chest hands-only CPR. Additionally, trained life support providers should focus on providing high quality chest compression with minimal interruptions. The AHA also recommends that dispatcher-assisted CPR should only provide instructions for hands-only CPR.²⁹

This shift from traditional CPR to hands-only CPR is intended to not only minimize the number of interruptions to chest compressions, but also increase the percentage of patients of  OHCA who receive CPR.⁸ A recent study found that only 51% of general public were willing to perform CPR on a stranger.³¹ Barriers to performing CPR included fear of incorrect technique, physical inability, legal liability, and fear of mouth-to-mouth contact. Educating the public on hands-only CPR could substantially increase the percent of OHCA victims who receive bystander CPR. 

Implementation of CPR Program 

When it comes to implementing an organizational CPR training program, the type, scale, and scope of training as well as testing and subsequent certification requirements need to be determined as these factors greatly affect cost and time commitment. Contingencies also should be made for members who are unwilling or physically unable to complete training. Teaching resources include classroom courses, videos, online training modules, and even mobile apps.^32-34 

Instructor-led BLS 4 to 6 hour classroom courses have traditionally been the mainstay of CPR training. A recent study analyzing the impact of 2, 4, and 7 hour trainings found that longer courses were associated with slightly better correct performance (92%, 94%, and 96%, respectively).³² Skill retention decreased at a similar rate in all groups after 12 months with no intervening intervention. However, if participants underwent 6-month retesting, there was no statistically significant difference in performance after 12 months. The AHA guidelines state that it is reasonable to use a shortened course format, provided that 6-month retesting is provided.³⁵

In order to assess psychomotor skills, courses commonly use manikins to simulate victims of cardiac arrest. These manikins can range from low fidelity torso trainers to sophisticated, highly realistic, whole body human simulators. However, there is conflicting data on the benefit of such high fidelity simulators.^36-38 One case-controlled study showed greater adherence to AHA guidelines in residents trained using high-fidelity manikins (68% vs 44%).³⁹ In contrast, a study comparing high-fidelity manikin to viewing a training video for neonatal resuscitation showed no difference in knowledge, confidence, or skills.³⁶ Another study examining the cost-effectiveness of high fidelity training found a slightly higher pass rate for students trained with high versus low fidelity simulators (88% vs 78%) but the cost was 3 times higher per passing student for those trained on the high fidelity simulators.³⁸ There is currently insufficient data to recommend for or against the use of high-fidelity in BLS training.³⁵

Interactive, independent learning resources to teach BLS have also been developed. A recently developed video-based self-instruction (VSI) program involved a 22-minute video and an inflatable manikin with feedback device.³² A study was conducted in which 285 adults without CPR training in the previous 5 years were randomized to receive no training, a traditional 4-hour classroom course, or VSI training. The VSI group showed statically significant improvement in overall adequate performance compared to both the untrained controls and traditional classroom courses. Another recent study compared VSI programs with and without an interactive component; results showed that after watching the instructional video, the overall adequacy of CPR increased from 6% to 15%. After the interactive portion of the training program, overall adequacy increased to 57%.⁴⁰ The AHA now recommends that short VSI courses with minimal or no instructor coaching, combined with hands-on practice (ie, practice while you watch), can be considered as an effective alternative to instructor-led basic life support.³⁵

Retesting and retraining is an important element of CPR education, as performance skills decrease rapidly after training.^34,41 A study comparing feedback methods found that the pass rate for overall assessment decreased rapidly after initial training.³⁴ In 6 weeks, the pass rate for students taught with traditional methods decreased from 90% to 62%. A separate study of CPR retention found that performance was significantly decreased at 3 months.⁴² With reassessment and retraining at 3 months, CPR knowledge at 6 months was equivalent to performance immediate after initial training. The AHA recommends that BLS recertification be performed every 2 years and that recertification and retesting should be performed more frequently, however, an optimal retraining schedule is still undecided.³⁵ 

There is currently no standardized national curriculum for dispatcher-assisted CPR training. The Resuscitation Academy, a group founded by members of King County EMS and Seattle Medic One, has developed a toolkit that outlines the entire process of creating a dispatcher-assisted CPR program.²⁶ This process includes achieving buy-in and leadership support, assessing existing resources, training, implementation, and monitoring feedback. Measurement and quality improvement are considered the cornerstone of a successful dispatcher-assisted CPR program. Objective metrics should be agreed upon to evaluate dispatcher performance and recordings of calls should be reviewed with dispatchers to assess performance.²⁹

Hesitations in Performing CPR 

• Agonal breathing. CPR is indicated for any person who is unresponsive and not breathing normally. After cardiac arrest has occurred, a victim may continue to breathe in an abnormal manner for several minutes. Gasping during cardiac arrest is a reflex that is mediated by the brainstem and is present in all mammals.⁴³ Gasping is associated with several physiologic mechanisms in the body and can improve cardiac output, gas exchange, and increase venous return to the heart. These brainstem mediated gasping breaths during cardiac arrest are commonly referred to as agonal breathing. Agonal breathing has been described by callers as “difficulties in breathing,” “breathing poorly,” “gasping,” “wheezing,” and “occasional breathing.”⁴⁴

In a review of 445 recorded OHCA emergency calls, agonal breathing was identified in 40% of cases.⁴⁵ Furthermore, agonal breathing was associated with increased incidence of ventricular fibrillation when compared to victims without agonal breathing (56% vs 34%). Since ventricular fibrillation is potentially treatable with defibrillation, these patients would be anticipated to have a higher survival rate. Indeed, the data showed that patients with agonal breathing were found to have a much higher rate of survival to hospital discharge (27% vs 9%). 

A larger study of 1218 OCHA patients found that the difference in survival to hospital discharge for patients with agonal breathing was even greater (39% vs 9%).⁹ The researchers concluded that agonal breathing is a common phenomenon and is associated with increased survival. Potential rescuers and dispatchers should be educated to perform CPR in the presence of gasping breaths. 

• Performing CPR on patient not in need. The risk of injuring a person suffering from OHCA is commonly cited as a reason for not performing CPR, however, the potential of causing injuries is typically low. A prospective cohort study examined 1700 case in which CPR instructions were given by a dispatcher. The data showed that 45% of patients were subsequently found not to be suffering cardiac arrest. Of the total cohort, 18% of patients had CPR initiated, but were not in cardiac arrest. Within this group, 12% experienced chest discomfort but only 2% suffered a bone fracture.⁴⁶ Note: No patient suffered visceral organ damage as a result of CPR while not in cardiac arrest. 

The take-away here is that dispatcher CPR may frequently result in CPR being performed on patients not in cardiac arrest, but the risk of injury by performing CPR on these patients is quite low.

• Further injuring the patient. Patients who are in cardiac arrest have a much greater chance of sustaining significant injury from CPR. Autopsies of 700 bodies on whom CPR was performed revealed frequent injures. These included fractures (of which, 32% sustaining rib fractures and 21% sustaining a sternal fracture), abdominal, and pulmonary complications. In less than 0.5% of cases, there was a heart or great vessel injury that the was considered life-threatening.⁴⁷ In comparison to the >90% mortality expected from OHCA,^4,25,48 the risk of causing a life-threatening complication is considered negligible. 

• Fear of reprisal. Currently, all 50 states have Good Samaritan laws in place.⁴⁹ In order to qualify as a Good Samaritan, a person must: act in good faith, not engage in gross misconduct, and not receive specific compensation. These regulations do not extend to healthcare workers in their place of employment if CPR falls under their job responsibilities. According to the AHA, no lay rescuer has ever been successfully sued for providing CPR.⁴⁹ Legal liability for organizations attempting to develop CPR programs is less clear as specific regulations vary among states. Persons planning to implement a CPR training program should consult their legal counsel for jurisdiction-specific advice. 

This article outlines the first 2 links in the chain of survival for OHCA patients by reviewing background information, evidence regarding specific actions, approach to interventions, and potential cost and complication of those interventions. The second part of this series will discuss the role of AEDs. 

Thomas Hartka, MD, MS, is an assistant professor and assistant research director in the department of emergency medicine at the University of Virginia. He also serves as the assistant medical director at the Center for Applied Biomechanics and performs research in prehospital resuscitation training. 

William J. Brady, MD, is a professor of emergency medicine and medical director of emergency preparedness and response at the University of Virginia and operational medical director of Albemarle County Fire Rescue. He is active clinically in emergency medical care at the University of Virginia and the surrounding region.

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