The History of Cardiopulmonary Resuscitation and Where We Are Today

Abstract

Cardiac arrest remains a leading cause of death worldwide and is a global health crisis. First described in the medical literature in the 18th century, modern cardiopulmonary resuscitation (CPR) with closed chest compressions has remained the standard of care since 1960. Despite exponential advances in basic science research and technological innovations, cardiac arrest survival remains a dismal 10%. The standard of care closed chest compressions provide only 20–30% of baseline cardiac output to the body. Have modern therapies plateaued in effectiveness? This article reviews the history of cardiac arrest, its therapies, and opportunities for future treatments. Through an exploration into the history of CPR and breakthroughs in its treatment paradigms, modern-day researchers and providers may find further inspiration to combat the cardiac arrest public health crisis.

1. Overview

An estimated 654,000 cardiac arrest cases occur in the United States every year [1]. Its incidence continues to increase across the globe as the rate of cardiovascular disease climbs. Cardiac arrest (CA) is deadly, with a quoted survival at a mere 10% in the US and just 2% globally [2]. Of those few persons who do survive their cardiac arrest, an estimated 90% experience neurological deficits [3]. CA is a public health crisis; current therapies are not enough.

Modern-day CPR focuses on restoring perfusion and ventilation to the body during CA. Closed chest compressions, however, are not nearly as effective as the native heart, providing only an estimated 20–30% of baseline cardiac output to the body [4]. Meaningful survival after cardiac arrest demands adequate perfusion of the vital organs, including the myocardium and brain; however, chest compressions of the highest quality only generate 10–25% of baseline myocardial blood flow and 50% of normal cerebral blood flow [5]. Here, we describe the evolution of modern medicine’s understanding of CA and its treatments (Figure 1).

2. CPR Unfolds—From Nostril Bowing to Cardiac Massage

The first accounts of resuscitation date back to biblical times. According to The Bible, God breathed life into man through the nostrils during man’s creation [6]. This belief is shared with other cultures and religions, evidenced by the Jewish Talmud Shabbat advising to blow into nostrils, and is said to provide the first mention of a successful tracheotomy in sheep [6]. The Bible also names two midwives, Siphrah and Puah, who reportedly used their own respiration to revive an infant [6].

The first reported mouth-to-mouth technique to artificially ventilate and resuscitate a human being was in 1732 by Scottish surgeon Dr. William Tossach. He described his efforts on a coal miner who had ingested toxic levels of a poisonous gas [7]. Tossach first wrote of his successful use of the technique in 1744 [8]. In his account, Tossach advocated for the use of mouth-to-mouth, stating that it was “very simple”, “absolutely safe”, and could “at least do no harm” [7]. The mouth-to-mouth method was later advanced with the introduction of using bellows rather than transferring expired air from one human to another in 1782 [8] (Figure 2).

The first delivery of static shock to an animal was in 1745 by way of a contraption called the Leyden jar, designed for the electrocution of small animals [9]. The use of electricity to countershock an arrested heart back into normal cardiac rhythm was then discovered in chickens in 1775 by Danish veterinarian Peter Abildgaard [8]. The discovery that electricity could resuscitate is attributed to research that was actually focused on arresting the heart through electric shock rather than restoring its rhythm. It was not until the late 1800s that ventricular fibrillation was recognized as a contributor to human death by British physiologist John McWilliam [9].

Resuscitation methods of the 19th century and earlier were centered around mechanical techniques of artificial ventilation [10]. French surgeon Dr. J.J.J. Leroy d’Etoilles is credited as the first to employ alternative anatomical positioning, like moving the arms above the head and then folding them down to the chest, to improve the effectiveness of artificial ventilation in 1827 [10].

Nearly a century after the first recorded uses of the mouth-to-mouth technique and electrical cardiac defibrillation, London physicians Drs. Marshall Hall and Henry Silvester instituted the concept of using an arrested victim’s own body and anatomical positioning to apply expiratory pressure to the chest to facilitate artificial ventilation in 1856 and 1858, respectively [8]. In 1868, John Hill of the Royal Free Hospital described a surgeon’s use of external sternal compression at a rate of 12 compressions per minute, with the aim of artificially respirating the patient rather than compressing the patient’s heart. Hill attributed the patient’s successful resuscitation to their inhalation of ammonia, which was applied to the nostrils of the patient through a soaked sponge. Similar to Tossach’s support of mouth-to-mouth ventilation, Hill concluded that the application of external sternal compressions was “simple in the extreme” and required “little or no assistance”.

In 1874, German physicist Moritz Schiff introduced open-chest cardiac massage as a method to restore circulation in animals [8]. Four years later, German pharmacologist Rudolph Boehm advanced Schiff’s research and proved that external cardiac massage of an arrested feline heart provided adequate circulation, showing that Schiff’s invasive technique was not required in all cases of cardiac arrest [8]. Fifteen years after Boehm’s work, in 1891, German surgeon Dr. Friedrich Maass performed the first successful use of rapid, vigorous external cardiac compression on two humans and was the first proponent of using this rapid, vigorous external cardiac massage technique in addition to artificial ventilation to effectively restore a patient’s circulation [10]. Prior to Maass’s discovery, external compressions were typically applied to the xiphoid process of the sternum rather than directly over the heart. Interestingly, Maass was the first in the development of CPR to comment on the concepts of consistency, quality, and timing of compressions, stating that as long as a patient’s state remained unimproved, “pausing infrequently and as briefly as possible” was critical to the patient’s survival [10].

Despite being revolutionary, Maass’ less invasive but more direct combination resuscitation technique did not gain strong traction in the medical world, and for the 50 years following his discovery, open-chest cardiac massage was the standard resuscitation technique [8]. The hesitation to adopt Maass’s technique has primarily been attributed to the universal lack of knowledge about cardiac arrest and its pathophysiology through to the mid-20th century. Medical professionals were not confident in data provided by animal studies like those of Schiff and Boehm. Before the turn of the century, circulatory collapse had primarily been encountered perioperatively, and thus, physicians viewed it as a surgical problem requiring a surgical solution. Similarly, out-of-hospital cardiac arrest was mainly encountered in victims of drowning and was thus considered strictly a ventilation-related condition. The mechanism behind myocardial infarction was not detailed until 1912 and was not diagnosed by electrocardiography until 1918 [10,11]. Lastly, the medical field viewed Maass’s proposed rate of 120 compressions per minute as inappropriate, given that prior to Maass, compressions were provided at a rate equal to the patient’s respiratory rate, or approximately 30–40 compressions per minute [10].

In 1903, the delivery of external chest compression was reevaluated by Ohio surgeon Dr. George Crile, whose research showed the method to be an effective life-saving technique in dogs. Crile’s work was confirmed 30 years later by a team of researchers at Johns Hopkins University and electrical engineer Dr. William Kouwenhoven, who replicated Crile’s technique in hundreds of canines, further confirming that external cardiac compression was an effective resuscitation technique. Crile continued his work and reported another successful use of external cardiac massage on a human heart in 1904. However, paralleling Maass’ experience, Crile’s method of closed-chest (external) cardiac massage did not gain traction, and open-chest cardiac massage remained the standard.

It was not until the mid-1900s that there was an increase in defibrillation research, credited to a post-World War II cultural change in the United States during which hospitals were identified as adequate intensive care centers [9]. Animal research on alternating current-inducing ventricular fibrillation and defibrillation by Kouwenhoven and Langworthy was conducted in 1930 [12]. In 1947, a cardiothoracic surgeon in Cleveland, Ohio, by the name of Dr. Claude Beck performed the first successful electrical defibrillation of an exposed human heart (open-chest method) [8].

Remarkably, except for its rate of and location of compression (sternal versus cardiac), the technique described by Hill was nearly identical to that CPR pioneer Dr. William Kouwenhoven published in 1960 [7]. Mouth-to-mouth resuscitation was officially proven to be an effective life-saving method by Drs. Elam and Peter Safar in 1956, after which the United States military adopted this method to resuscitate unresponsive victims in 1957. In the same year of 1956, Harvard cardiologist Dr. Paul Zoll performed the first successful external defibrillation of a human heart (closed-chest method) [8]. These defibrillators were large and bulky and meant to be operated in a hospital setting. One year later, in 1957, a team at Johns Hopkins University composed of Drs. Kouwenhoven, James Jude, and Guy Knickerbocker released the first portable external defibrillator [3,8]. Nearly a decade later, in 1966, Dr. Frank Pantridge used the first out-of-hospital defibrillator in an ambulance [3]. The modern automated external defibrillator (AED) was invented in 1978 and became available for public use in the 1980s [3].

It was not until the official creation of modern CPR and its subsequent advocacy to physicians by the soon-to-be-formed American Heart Association that closed-chest cardiac massage (chest compressions) became the standard in CPR [8]. In 1924, six cardiologists in Chicago, motivated by the high level of ignorance surrounding heart disease, founded the American Heart Association (AHA), and from this alliance, modern-day CPR began to take form (Figure 3). The AHA held its first Scientific Sessions meeting in 1925, where physicians and other medical professionals across the country were educated about the most recent advances and knowledge of cardiology and heart disease. These sessions continued annually and swiftly became the largest meeting on cardiovascular health in the country [13]. In 1960, Drs. Kouwenhoven, Knickerbocker, and Jude combined the early discovery of mouth-to-mouth artificial ventilation and the later discovery of closed-chest cardiac massage (compressions) into the modern CPR method and published their seminal research in the July 1960 issue of the Journal of the American Medical Association [13,14]. Their paper emphasized novel and nuanced aspects of CPR, like how the focus of CPR delivery would change if only one person were available to provide chest compressions (in which case high-quality compressions should be this person’s focus), compared to two or more available persons (in which case one would provide compressions and the other would provide mouth-to-mouth ventilation) [14]. Dr. Safar noted that sternal compressions alone do not sufficiently ventilate lungs, and thus, “Steps A, B, C” were born to represent airway, breathing, and circulation as the pillars of resuscitation [15].

To aid in the dissemination of Drs. Kouwenhoven’s, Safar’s, Jude’s, and Knickerbocker’s research, the AHA launched the first closed-chest CPR training program for physicians that eventually became the foundation for the public CPR training courses the AHA is known for today [8] (Figure 4). Cardiologist Dr. Leonard Scherlis founded the AHA’s CPR Committee in 1963, the same year that the AHA officially endorsed CPR as a life-saving method [8]. It was not until 1969 that, after repeated requests from the American Red Cross, the National Academy of Science’s National Research Council held an ad hoc CPR conference from which standardized CPR training and performance guidelines were established [8]. From this point forward, the AHA became the authority for CPR training guidelines across the country with their publication of the first Advanced Cardiovascular Life Support (ACLS) textbook in 1975, introduction of the first telephone CPR training program for use by emergency dispatch personnel in Washington in 1981, development of the first guidelines for use of CPR in children and neonates in 1983, introduction of the first pediatric basic life support (BLS), pediatric ALS (PALS), and neonatal resuscitation training programs in 1988, and the creation of the first public-access defibrillation training programs and automated external defibrillation (AED) devices in 1990 [8].

The AHA has continued its advocacy and advancement of CPR education into the 21st century with its approval of AED use in children between the ages of 1 and 8 years old in 2004 and the release of the Family and Friends CPR Anytime Kit^® in 2005, a product developed to enable any layperson to learn the foundational skills needed to provide CPR, AED, and choking relief at any location in just 20 min. It was also in 2005 that the first AHA Guidelines for CPR and Emergency Cardiovascular Care (ECC) were released, to which updates were published in 2010 and 2015. To further advance the availability and usage of CPR and AED in public locations, the AHA began its implementation of interactive CPR kiosks in major cities across the country in 2013, with the Dallas Ft. Worth airport being the first site. The AHA’s latest statement on CPR education strategies to improve outcomes in cardiac arrest was published in 2018 and is intended to be applicable to all CPR training courses and not just those developed by the AHA [8].

3. CPR Today

Modern-day CPR was formed from the basic principles revealed by Kouwenhoven in 1960 [14]. Medical providers and trained professionals provide CPR using external chest compressions and mouth-to-mouth breathing at a ratio of 30:2 compressions to breaths. The average adult victim should receive 100 to 120 chest compressions per minute, the depth of which should not exceed two inches. The AHA advises that bystander witnesses of an adult OHCA event should provide “hands-only” CPR, which removes the mouth-to-mouth ventilation component described above [17]. First emphasized by Maass in 1891, the importance of providing high-quality CPR remains a universal focus across the AHA’s CPR guidelines, various CPR training programs, and existing CA outcomes literature. To do so, the provider of CPR should focus on limiting interruptions of compressions, providing the recommended rate and depth of compression, avoiding resting against the victim between compressions, maintaining proper hand positioning on the chest, and avoiding excessive ventilation of the victim [17].

While closed-chest CPR (CCCPR) is the primary resuscitation method that comes to mind when discussing CPR and its public use, open-chest CPR (OCCPR) exists as an alternative technique to be used in specific clinical circumstances. However, whether CCCPR or OCCPR results in greater patient survival outcomes and in which clinical circumstances each method results in better outcomes is often debated. A 2020 retrospective multicenter cohort study by Endo et al. found that compared to CCCPR, OCCPR was associated with significantly higher survival to hospital discharge (STHD) in severe trauma patients showing signs of life upon hospital arrival [18]. Jouffrey and Vivien add that OCCPR is especially effective in the case of penetrating traumas [19]. A 2019 systematic review and meta-analysis of seven observational studies (no comparative randomized controlled trials existed in the literature) by Wang et al. concluded that there were no significant differences in return of spontaneous circulation (ROSC) and STHD between CCCPR and OCCPR in CA patients [20]. Subgroup analysis of CA patients with trauma showed that CCCPR was associated with a higher ROSC compared to OCCPR. Conversely, subgroup analysis of CA patients without trauma showed that OCCPR was associated with greater ROSC compared to those treated with CCCPR [20].

With the implementation of AEDs in the 1980s came the rollout of public-access defibrillation (PAD) programs. Early programs focused on placing AEDs in high-traffic public spaces or places where the EMS response may be delayed, like on an aircraft [3]. These programs experienced early success, with observational studies reporting relatively high survival rates for those defibrillated with no incidents of inappropriate shocks or injuries [3]. This influenced placement into other large public event places and the heterogenous PAD programs we see today were born. The Public Access Defibrillation trial published by Hallstrom et al. in 2004 was a randomized controlled trial assessing the impact of AED utilization in bystander CPR on patient survival [8]. The use of AEDs increased patient survival to hospital discharge [21]. An analysis from the Resuscitation Outcomes Consortium estimated that 474 lives are saved every year in the US and Canada with current AED use [3]. Impressively, The HeartRunner Trial utilized smartphone app-dispatched citizen responders whose presence (prior to that of EMS) was associated with a 3-fold increase in the odds of bystander defibrillation [22].

These events remain difficult to study due to their emergent nature and short time course. Traditionally, the continuation of CPR beyond 15 min or when more than two doses of epinephrine have been administered is considered futile [5]. However, it is increasingly common to see CPR efforts performed beyond these parameters, and with positive outcomes. These outcomes may be attributed to improvements in CPR quality and post-resuscitation care. For example, Yamaguchi et al. found that in a cohort of patients from 1998 to 2013, factors including bystander CPR, non-EMS AED shock, public location of arrest, and witnessed arrest, amongst others, were associated with greater OHCA survival [23].

3.1. Telecommunicator CPR

First introduced in 1981 in King County, Washington, telecommunicator CPR (T-CPR) holds a crucial role in improving outcomes in out-of-hospital cardiac arrest (OHCA) events by doubling rates of bystander CPR [24]. T-CPR is when a caller who has identified a person in cardiac arrest may communicate with a telecommunicator who will provide CPR instructions and dispatch appropriate emergency personnel. The existing literature reports that survival decreases by 5% every minute between the onset of an OHCA event and the initiation of CPR and that anoxic cerebral injury occurs just a few moments after the onset of CA [24]. T-CPR has been shown to increase survival rates of OHCA by more than 200% [24]. T-CPR received support from the AHA in their 2010 Guidelines for CPR and ECC and was graded with the highest level of recommendation in its 2017 update. Despite its impact and recommendations, it is still only present in less than 50% of all public safety answering points. However, successful community-wide efforts to increase T-CPR provision and utilization and delivery of bystander CPR have been reported across the country (Figure 5).

A 2007–2010 study conducted in Phoenix, Arizona, acts as an example of the effectiveness of implementing a T-CPR care plan, which includes guideline-based protocols, training, data collection, and feedback to two regional dispatch centers. The study reported a 9.3% increase in T-CPR, 3% increase in all-rhythm survival, 10.3% increase in survival after shockable rhythm, and 2.7% increase in favorable functional outcomes [24]. There is consistent implementation of similar programs in King County and Seattle, Washington, whose 2023 EMS Annual Report boasts a bystander CPR rate of 71%, a correctly identified CA by telecommunicators rate of 96%, and an overall bystander-witnessed OHCA survival rate of 47% [24,25]. Barriers to the success of T-CPR programs exist, such as patient positioning and the location and ability of a bystander to physically provide effective chest compressions to an OHCA victim [24]. Furthermore, disparities related to CPR training may impact bystander CPR utilization and the success of T-CPR programs. The median CPR training rate in the US in 2022 was 2.39%, with a reported current training prevalence of 18% [26]. A 2017 cross-sectional survey of adults in the US found that CPR training may improve how a bystander responds to T-CPR instruction and their willingness to perform T-CPR [27]. Notably, older age was associated with a lower likelihood of CPR training, and higher socioeconomic status was associated with a higher likelihood of CPR education [27]. Efforts to better characterize specific populations to target for training have been made. Ultimately, it is important to tailor bystander CPR and T-CPR training programs to meet the needs and level of education of specific populations across the country [27].

3.2. ECMO CPR

The first application of extracorporeal circulation used in the treatment of cardiac arrest was in 1976 at Baylor in Houston, Texas. Extracorporeal cardiopulmonary resuscitation (ECPR) utilizes extracorporeal membrane oxygenation (ECMO) during conventional CPR to assist the body in end-organ perfusion. Two landmark randomized controlled trials, the ARREST trial and the Prague OHCA trial, have suggested a survival benefit of ECPR for OHCA [28,29]. However, ECPR survival rates reported are heterogeneous and range from 15 to 60% [30]. Another randomized controlled trial (INCEPTION) showed no significant survival benefit but a more favorable neurologic outcome [31]. Richardson et al. describe patient outcomes after receiving ECPR by analyzing extracted data from the Extracorporeal Life Support Organization (ELSO) over a 12-year period from 2003 to 2014 [30]. They found a survival to hospital discharge rate of 29% for patients receiving ECPR, with no change in outcomes over this 12-year period [30]. More patients are treated with ECPR today, although the proportion of those treated who survive has not improved [5,30,32]. The ELSO Registry reported an increase from less than 100 instances annually in 2009 to over 1500 annual instances in 2019 [32].

While the AHA recognizes ECPR as an advanced rescue therapy, much remains to be investigated about its use. Limitations to ECPR and topics of controversy today include the lack of an unequivocal definition of ECPR, correct timing of initiation, optimal patient selection, resource availability, post-resuscitation care, economic impact, and ethical considerations [32,33,34]. Despite these unknowns, ECPR has the potential to improve patient outcomes after CA.

3.3. Pediatric Resuscitation

More than 20,000 American children suffer from CA every year [35]. Historically, pediatric CPR guidelines have been extrapolated from adult guidelines; however, substantial differences exist between the two populations. Causes of pediatric CA differ from those of adults and often stray from underlying disease processes. There are even differences in the initial arrest rhythms [35]. Outcomes in pediatric CA are particularly poor, with the quality of basic ALS and the environment in which cardiac arrest occurs being critical influencing factors [5]. First developed in 1988, Pediatric Advanced Life Support (PALS) focused on CA prevention and treatment of respiratory failure and shock as opposed to treating CA itself [5].

Compression rate and fraction in pediatric CPR are equal to those of adult CPR, whereas the recommended depth of compression in pediatrics is lower (one-third of the anterior-posterior chest depth) [36]. Though the recommended pediatric ventilation rate matches that of adults, these guidelines have been criticized for not considering the greater baseline heart rate and ventilation rate of children. Furthermore, a multicenter study assessing ventilation rates provided during in-hospital pediatric CPR found that ventilation rates exceeded consensus guidelines in every event with rates >30 breaths/min in children under 1 year of age and >25 breaths/min in older children and were associated with improved survival [37]. The pediatric population has gained special attention since the introduction of PALS in 1988; however, there is far less documented data in the history and literature for this population and, therefore, opportunity for significant advances.

4. CPR Research Today

Traditional ACLS interventions strive to supply patients with adequate coronary perfusion pressure but remain unsuccessful, even under optimal conditions [38]. Stubbornly high mortality and associated morbidity call for significant innovations to supplement modern-day chest compressions.

The quality of chest compressions is a known determinant of patient survival. Not only is it essential for chest compressions to be uninterrupted and conducted at a sufficient rate, but sufficient compression depth is also imperative for survival. Audiovisual CPR feedback technologies use force sensors and accelerometers in conjunction with verbal feedback to guide the rescuer with information about quality compressions. These devices are in use today with varied popularity and effectiveness on survival, as described by randomized controlled trials [34]. Advancements in improving respirations have also been studied, including a ventilation timing light that prompts users to initiate respiration and monitors duration to improve consistency [39]. A defibrillator combined with the use of real-time audio feedback has also been used to improve ventilation quality [40].

Mechanical CPR devices were introduced to minimize compression variability and interruptions; however, the benefit of these devices over manual compressions has not yet been proven in the literature [41]. Current commercially available devices include the Lund University Cardiopulmonary Assist System “LUCAS” (Stryker Medical, Kalamazoo, MI, USA), the Autopulse (ZOLL Medical Corporation, Chelmsford, MA, USA), and the Thumper (Michigan Instruments, Grand Rapids, MI, USA). These devices are helpful today in scenarios where reliable manual chest compressions cannot be performed and may be used in the future for titrating compression rates along with physiological endpoints [42]. Studies on chest compression-synchronized ventilation have shown promising, although conflicting, results in animal models, necessitating further research. This phenomenon is based on the idea raised by Criley et al. in 1976 that the change of airway pressure through a cough produces a short burst of blood flow without compressions [43].

Neuroprotection is a primary focus in resuscitative research, as cerebral circulation and oxygen delivery to the brain depend on cardiac output. Drug therapies are under investigation to combat the adverse effects of epinephrine on capillary constriction and the no-reflow phenomenon [44]. Additionally, neuroprotective strategies are a huge focus of post-resuscitation care, including rehabilitation for the lasting physiologic effects of a no- or low-flow state to the brain. In efforts to improve ischemic brain damage after cardiac arrest, targeted temperature management was introduced with recommendations for therapeutic hypothermia of 32–36 degrees Celsius in post-cardiac arrest patients based on two trials [45,46,47]. Maintaining adequate blood pressure targets both during CA and after ROSC affects survival [48]. Bilateral lower extremity tourniquets have been shown to increase blood pressure and may present an emerging technique for hemodynamic support in hypotensive patients [49].

More invasive therapies also exist. The resuscitative endovascular balloon occlusion of the aorta (REBOA) was initially introduced in the 1950s for hemorrhage control and has recently been studied in cardiac arrest to improve coronary perfusion pressure and cerebral blood flow [39]. The REBOA is less invasive than a resuscitative thoracotomy; however, it remains limited in its use to the hospital setting. Selective aortic arch perfusion (SAAP) is another strategy to facilitate ROSC, specifically for exsanguination cardiac arrest, which requires further clinical trials [50]. A new area of research includes computer-based CPR protocols. Daudre-Vignier et al. found that an optimized CPR protocol generated through computational modeling outperformed current CPR guidelines, increasing both myocardial and cerebral tissue oxygen volume [51]. As our computational and analytical technologies evolve, future opportunities may exist to explore computer-generated personalized or tailored CPR efforts.

Defibrillation research today focuses on the optimal number and form of electrical shocks. A stacked shock strategy, meaning one shock after another for up to three consecutive shocks, is one proposed method that has yielded mixed results on superiority or inferiority to one single shock. Biphasic vs monophasic shock waveforms have also been studied in the 21st century with conflicting results on success. It is said that the first biphasic waveform experiments should be credited to Kouwenhoven, first reported in an engineering journal [12]. Additionally, research is being carried out for automated rhythm classification by reducing ECG artifact.

While there are many reporting registries across the globe, they are more numerous in North America and Europe, not providing equitable population coverage [52]. This makes multinational, large-scale research for cardiac arrest difficult. Beyond the development of technology, significant research efforts in critical care focusing on system-based and environmental factors, such as code team optimization, training optimization, interdisciplinary training, and post-cardiac arrest care, are equally important [45].

5. Conclusions

Cardiac arrest remains a disease associated with high mortality and morbidity. Despite centuries of medical and technical knowledge, the practice of CPR has seen relatively little evolution or innovation. Therapeutic strategies for CA are challenging to study in the clinical setting due to physical and ethical constraints, limiting the opportunity for investigative medicine to make profound advancements. This review hopes to humble and inspire those who provide CPR for their patients and demonstrates the tremendous opportunity for further innovation in techniques, adjunctive technologies, and systems to combat this public health crisis.