Most Important Outcomes Research Papers on Cardiac Arrest and Cardiopulmonary Resuscitation

Abstract

HomeCirculation: Cardiovascular Quality and OutcomesVol. 7, No. 2Most Important Outcomes Research Papers on Cardiac Arrest and Cardiopulmonary Resuscitation Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBMost Important Outcomes Research Papers on Cardiac Arrest and Cardiopulmonary Resuscitation Karthik Murugiah, MD, Serene I. Chen, AB, Kumar Dharmarajan, MD, MBA, Sudhakar V. Nuti, BA, Brian Wayda, MPH, Abbas Shojaee, MD, Isuru Ranasinghe, MBChB, MMed, PhD and Rachel P. Dreyer, PhDfor the Editor Karthik MurugiahKarthik Murugiah Search for more papers by this author , Serene I. ChenSerene I. Chen Search for more papers by this author , Kumar DharmarajanKumar Dharmarajan Search for more papers by this author , Sudhakar V. NutiSudhakar V. Nuti Search for more papers by this author , Brian WaydaBrian Wayda Search for more papers by this author , Abbas ShojaeeAbbas Shojaee Search for more papers by this author , Isuru RanasingheIsuru Ranasinghe Search for more papers by this author and Rachel P. DreyerRachel P. Dreyer Search for more papers by this author and for the Editor Originally published1 Mar 2014https://doi.org/10.1161/CIRCOUTCOMES.114.000957Circulation: Cardiovascular Quality and Outcomes. 2014;7:335–345Other version(s) of this articleYou are viewing the most recent version of this article. Previous versions: January 1, 2014: Previous Version 1 IntroductionCardiac arrest is a common and treatable cause of death and disability. Each year ≈424 000 people experience emergency medical services (EMS)-assessed out-of-hospital cardiac arrest (OHCA) in the United States.1 The actual burden of OHCA is likely significantly higher because a substantial number go unassessed. In a prospective analysis of deaths in a US county, 5.6% of annual mortality was attributable to cardiac arrest.2 Many patients who suffer OHCA do not receive prompt cardiopulmonary resuscitation (CPR). Among those who receive CPR, a large number do not survive because of an inability to restore spontaneous circulation, or anoxic cerebral injury even after restoration of circulation. Nevertheless, when timely interventions are provided, a small proportion of patients (10.4% of all EMS-treated OHCA) recover to resume normal lives. The key therapeutic interventions that make the difference between life and death, metaphorically characterized as the 5 links in a chain of survival by the American Heart Association, include: (1) immediate recognition of cardiac arrest and activation of the EMS, (2) early CPR with emphasis on chest compression, (3) rapid defibrillation, (4) effective advanced life support, and (5) integrated postcardiac arrest care.3Resuscitation science has undergone major advances since the origins of modern CPR >50 years ago.4 The field continues to be dynamic with emergence of new therapies such as therapeutic hypothermia5 and improvements in systems of care. However, many questions remain on issues such as optimum compression rate, efficacy of chest compression only CPR (CCCPR), dispatcher-assisted CPR, and benefits of postresuscitation measures such as hypothermia. A critical challenge also lies in the translation of resuscitation science into practice. To improve outcomes, each of the links in the chain of survival needs to be executed promptly and effectively. There remain several lacunae, which need to be overcome to develop an effective resuscitation system. For example, the failure to recognize cardiac arrest, low bystander rates of CPR, variation in CPR quality, defibrillator availability and use, EMS response, and variation in quality of postresuscitation care are all areas presented under investigation. Systematic assessment of resuscitation performance at community, first responder, and hospital levels are crucial to devise and institute targeted intervention.In the following Topic Review for Circulation: Cardiovascular Quality and Outcomes, we focus on articles that address these challenges. We included articles that evaluate (1) the epidemiology of cardiac arrest and its outcomes, (2) the predictors of successful CPR, (3) community access to CPR and automated external defibrillators (AEDs), and (4) acute postresuscitation care.Epidemiology of Cardiac Arrest and Its OutcomesThe incidence of cardiac arrest parallels the burden of cardiovascular illnesses, with cardiac arrest as the cause of death in >60% of patients with known coronary artery disease.6 Based on the data from the 2011 Resuscitation Outcomes Consortium, two thirds of OHCAs occur at home or at a residential location.7 Of ≈211 000 patients treated by EMS, 40.8% receive bystander CPR before EMS arrival,1 and 23% have ventricular arrhythmias as the initial rhythm.8 The incidence of cardiac arrest with an initial rhythm of ventricular fibrillation (VF), which carries a better prognosis,9 is decreasing over time10; however, the overall incidence of cardiac arrest remains unchanged. Cardiac arrest continues to have a grave prognosis with an estimated survival of 10.4% for EMS-treated cardiac arrest of any rhythm and 31.7% for bystander-witnessed shockable rhythm.1 Another 209 000 cardiac arrests occur within the in-hospital setting, with ≈22.7% survival among adults.11There is wide regional and temporal variation in the incidence and outcomes of OHCA and in-hospital cardiac arrest.6,8 The incidence and outcomes are influenced by several determinants, such as variation in risk factors, socioeconomic differences, differences in bystander CPR, EMS response, and provision of acute and postresuscitation care. The following section summarizes studies describing the epidemiology of cardiac arrest and its outcomes.Survival Trends in Pediatric In-Hospital Cardiac Arrests: An Analysis From Get With The Guidelines–ResuscitationSummary: There are limited data on survival trends among pediatric patients who suffer an in-hospital cardiac arrest. The authors analyzed the Get With The Guidelines (GWTG)-Resuscitation registry to evaluate children (<18 years of age) with in-hospital cardiac arrest between 2000 and 2009 at hospitals with >3 years of participation and >5 cases annually. Outcomes measured were acute and postresuscitation survival and neurological disability. Of the 1031 pediatric in-hospital cardiac arrests from 12 hospitals, the initial cardiac arrest rhythm was asystole or pulseless electric activity (PEA) in 84.8% of children and VF or pulseless ventricular tachycardia (VT) in 15.2%. The proportion of cardiac arrests with specifically PEA increased from 26.6% during 2000 to 2003 to 70.3% during 2007 to 2009 (P<0.001). Over time, the proportion of newborns also increased, as did the proportion with arrest in the intensive care unit, patients on mechanical ventilation and vasopressors. Conversely, the prevalence of heart failure (HF), respiratory insufficiency, and baseline depression in neurological status among children with cardiac arrest decreased. Overall, 34.8% survived to hospital discharge. Risk-adjusted rates of survival to discharge increased from 14.3% in 2000 to 43.4% in 2009 (P for trend=0.02). This improvement was observed across age groups and initial cardiac arrest rhythm. Acute resuscitation survival increased from 42.9% to 81.2% (P for trend=0.006). Postresuscitation survival increased over time but was not significant (P=0.17). There was no change in postcardiac arrest neurological disability. The use of extracorporeal membrane oxygenation during resuscitation increased from 8.1% in 2000 to 2003 to 14.3% in 2007 to 2009 (P for trend=0.004); however, its use was not associated with overall survival to discharge.Conclusion: The authors highlight an improvement in post– in-hospital cardiac arrest survival from 2000 to 2009. Improvement in acute resuscitation survival chain is likely an underlying reason for the betterment in outcomes. An important finding is the increased proportion of cardiac arrests due to PEA and a corresponding decrease in cardiac arrests due to asystole and VF/pulseless VT. As acknowledged by the authors, higher levels of monitoring may have led to earlier detection of cardiac arrest (specifically PEA). The improvement in survival is even more significant given the poor prognosis of PEA arrest; however, the proportion of arrests due to asystole, which carries an even worse prognosis, decreased as well.12–14Nationwide Improvements in Survival From Out-of-Hospital Cardiac Arrest in JapanSummary: There is global variation in the incidence and outcomes of cardiac arrest.15 Japan has experienced a dramatic increase in public access to AEDs,16 with a continued push for citizen CPR training. This study evaluated the trends in incidence and outcomes of bystander-witnessed OHCA in Japan from 2005 to 2009 using the All-Japan Utstein Registry of the Fire and Disaster Management Agency and further characterized events by the origin of OHCA and initial rhythm. During the 5 years, there were 547 153 confirmed OHCAs, and the incidence rate per 100 000 persons increased from 80.7 in 2005 to 90.4 in 2009. Of these, 174 068 OHCAs were bystander-witnessed. The incidence rate of overall bystander-witnessed OHCAs significantly increased from 24.0 in 2005 to 28.5 in 2009. Of the 169 360 patients selected for analysis, 42.9% received bystander CPR, and this proportion increased from 36.6% in 2005 to 48.4% in 2009 (all P<0.001). The proportion of CCCPR increased from 47.5% to 70.2%. The cause was presumed cardiac in 56.1% patients, and initial rhythm (VF) was in 15.4%, which increased over the period from 14.6% to 16.2%. The proportion of patients shocked using public-access AEDs increased from 0.2% to 1.8%. At the same time, there was also an increase in epinephrine administration (0.0–15.5%) and endotracheal intubation (3.4–9.5%) by EMS (all P<0.001). Neurologically favorable survival among bystander-witnessed OHCA increased from 2.1% in 2005 to 4.3% in 2009 and for bystander-witnessed VF OHCA from 9.8% to 20.6% (both P<0.001). In multivariate analysis, public-access AED use, bystander CPR, and earlier EMS response time were associated with a better neurological outcome.Conclusion: National initiatives in Japan have led to increased rates of CPR and public AED use. The authors demonstrate a translation into improvements in outcomes of OHCA from 2005 to 2009. Although the outcomes may have been influenced by advancements in quality of advanced life support by EMS personnel and subsequent postresuscitation care, increased bystander CPR is likely an important factor driving this improvement.17Post-Cardiac Arrest Mortality Is Declining: A Study of the US National Inpatient Sample 2001 to 2009Summary: The past decade has seen changes in resuscitation guidelines, increased public access to AEDs,18 impetus to widen community CPR awareness, and improvements in postresuscitation care. This study describes trends in post–cardiac arrest survival in the United States using the Nationwide Inpatient Sample (NIS) database from 2001 to 2009. Patients hospitalized with cardiac arrest were identified using the International Classification of Diseases, 9th Edition, Clinical Modification (ICD-9-CM) code 427.5. The primary end point was in-hospital mortality. The analysis was stratified by age, sex, race, and the Charlson Comorbidity Index. A total of 1 190 860 patients were hospitalized with a diagnosis of cardiac arrest in the United States from 2001 to 2009. The in-hospital mortality rate declined each year from 69.6% in 2001 to 57.8% in 2009 (P<0.001) despite the fact that the proportion of patients with higher comorbidity scores increased over time (Charlson Comorbidity Index ≥4 increased from 5.1% to 12.4%). Mortality declined in all subsets of patients by sex, age, race, and comorbidity index. This decrease in mortality was more prominent in patients with higher comorbidity index and black race. In multivariate analysis, older age, female sex, higher comorbidity index, nonwhite race, and earlier year were independent predictors of increased risk of in-hospital death.Conclusion: This study shows a declining trend in mortality from cardiac arrest. The drivers of this decline are likely multifactorial, including improvements in the chain of survival, but the nature of the study data precludes assessment of individual determinants. The reported mortality rates are much lower than those reported from the GWTG-Resuscitation registry19 and another analysis using the California State Inpatient Database database.20 There are certain limitations to this administrative data–based study. The authors used the ICD code 427.5 in either primary or secondary discharge diagnosis category, and hence the location of cardiac arrest could have been either in-hospital or outside. The usage of this code in any discharge diagnosis category is not validated.21–23 In addition, patients with cardiac arrest secondary to ventricular arrhythmias may have been coded using specific ICD code such as VF (427.41) instead of the cardiac arrest ICD code.24Association Between a Hospital’s Quality Performance for In-Hospital Cardiac Arrest and Common Medical ConditionsSummary: The benefit of an additional publically reported inpatient survival measure for cardiac arrest is unknown. The authors examined the relationship between hospitals’ survival rate for cardiac arrest and their mortality rate for 3 publicly reported conditions: acute myocardial infarction, HF, and pneumonia, with the hypothesis that a strong correlation may suggest that an additional measure would be redundant. This study used the GWTG-Resuscitation registry25 (2007–2010) and, using hierarchal logistic regression and adjusting for confounders, calculated hospitals’ risk-standardized survival-to-discharge rates for in-hospital cardiac arrest. The Centers for Medicare and Medicaid Services Hospital Compare Website was used to obtain 30-day risk-standardized mortality rates for acute myocardial infarction, HF, and pneumonia for the same time period. Outcomes were linked at the hospital level through American Hospital Association identification numbers. Weighted Pearson correlation coefficients were adopted to compare performance. The final cohort consisted of 26 270 patients enrolled from 130 US hospitals presenting with in-hospital cardiac arrest. The survival rate varied across hospitals (median risk-standardized rate, 22.1%; interquartile range, 19.7–24.2%). There was no significant association between hospitals’ outcomes for cardiac arrest with their outcomes for acute myocardial infarction (correlation, −0.12; P=0.16), HF (−0.05; P=0.57), or pneumonia (−0.15; P=0.10).Conclusion: This study demonstrates no significant correlation between hospitals’ cardiac arrest survival rates and 30-day mortality rates for 3 publicly reported common medical conditions. Thus, because there is substantial variation in survival rates of cardiac arrest across hospitals, public reporting of outcomes could provide additional novel information about hospital-wide effects on quality. These findings are important and may drive resuscitation-specific interventions to improve in-hospital cardiac arrest survival. As the authors note, limitations include the fact that adjustments could not be made for severity of illness, and they were able to compare cardiac arrest survival with mortality outcomes for only a few conditions. Lastly, data are lacking in regard to functional/neurological status at discharge and on hospital variation in their treatment regarding end-of-life care, which are important variables in this population.26Impact of Changes in Resuscitation Practice on Survival and Neurological Outcome After Out-of-Hospital Cardiac Arrest Resulting From Nonshockable ArrhythmiasSummary: Among patients with OHCA, survival from shockable arrhythmias (VT/fibrillation) has improved in recent years after the implementation of guidelines increasing the time devoted to chest compression during resuscitation.27,28 These changes include reducing the number of back-to-back rhythm analyses/shocks, eliminating rhythm and pulse checks after each shock, and increasing the ratio of chest compressions to ventilations. To test whether these guidelines have resulted in improved outcomes for nonshockable rhythms (asystole and PEA), the authors studied 3960 patients with nontraumatic OHCA from nonshockable rhythms in Kings County, WA. From January 2000 to January 2005, 1774 patients were included (preguideline revision), and 2186 patients were included from January 5 to March 10 (postguideline revision). The primary outcome was 1-year survival. Differences in survival between the 2 time periods were assessed using both standard logistic regression and segmented regression of interrupted time series data. The percentage of patients with OHCA with nonshockable rhythms increased from 64% to 69% between periods; however, the distribution of arrests attributed to asystole (65%) and PEA (35%) remained similar over time. Patient demographic and resuscitation characteristics were comparable except for the percentage of patients receiving bystander CPR, which was lower in the earlier period (48% versus 57%). One-year survival increased from 2.7% to 4.9% after guideline revision and was found to be significantly higher after covariate adjustment by regression analyses. No progressive temporal trends in survival were identified over the full 10-year period.Conclusion: Through the use of multiple analytic methods, including the demonstration that 1-year survival increased rapidly after the institution of new resuscitation protocols, the authors provide support for new guideline recommendations for persons with cardiac arrest from nonshockable rhythms. Findings are particularly important in that nonshockable rhythms comprise an increasing percentage of cardiac arrest cases.10 Findings will need to be replicated in settings without long-established and data-driven emergency medical systems and will need to demonstrate greater assurances about residual confounders. In this instance, bystander resuscitation was much more common in the latter period, as was the total percentage of arrests from nonshockable rhythms.29Incidence, Causes, and Survival Trends From Cardiovascular-Related Sudden Cardiac Arrest in Children and Young Adults 0 to 35 Years of Age: A 30-Year ReviewSummary: Sudden cardiac arrest (SCA) in the pediatric and young adult population is poorly characterized. Previous incidence estimates range from 0.5 to 20 per 100 000 person-years, and the contribution of specific causes is unknown. Meyer et al30 derive population-based estimates of age- and cause-specific incidence of SCA in young population from the King County (Washington) EMS Cardiac Arrest Database. To ascertain the cause and outcome, the authors examined all available medical records including EMS, hospital, and autopsy reports. Among all patients up to 35 years of age, the incidence of cardiovascular-related OHCA was 2.28 per 100 000 person-years. Prevalent causes of OHCA included congenital abnormalities among those 0 to 13 years of age, presumed primary arrhythmia in those aged 14 to 24 years, and coronary artery disease in those aged 25 to 35 years. Meanwhile, hypertrophic cardiomyopathy—previously identified as a leading cause of SCA in young athletes—represented only 4% of cases in this study of the general population. Survival rates in OHCA increased from 13% in 1980 to 1989 to 40% in 2000 to 2009 (P<0.001), though incidence, age distribution, cause, and response times were not different over time.Conclusion: This study provides the most reliable estimates to date on the incidence and causes of SCA in the young population. These findings can inform the feasibility, design, and cost-effectiveness of cardiac screening programs in the pediatric population. The observed increase in SCA survival over time may reflect the efficacy of current resuscitation protocols. However, the reported survival rate (40%) in this study contrasts with contemporary estimates in other study populations, which are as low as 6%.31 Further studies are required to understand the reasons for this variation and the determinants of SCA survival in the young.30Advance Directives in Community Patients With Heart FailureSummary: HF carries a median mortality of 5 years in the community, though little is known about the completion of advanced directives (ADs) in this population. ADs include living wills and other documents specifying preferences for healthcare decisions in the event of severe illness and incapacity. The authors enrolled 608 patients with a diagnosis of HF from Olmsted County, MN, to assess AD completion at the time of enrollment, predictors of AD completion, content of ADs, and association of AD completion with care received in the last month of life. Data were abstracted from medical records via a centralized medical record linkage system in the Rochester Epidemiology Project.32 Consent rate for participation was 74%. Among included patients, the mean age was 74 years, 55% were men, 50% had preserved ejection fraction, and 65% had functional class III or IV symptoms. Nonconsenting patients were older (78.6 years) and more likely to be women (53.4%). Overall, 41% had an AD completed at the time of enrollment. Among patients with ADs, 90% designated a proxy decision maker, but only a minority commented on preferences for CPR (41.4%), mechanical ventilation (38.6%), artificial nutrition/hydration (38.6%), and hemodialysis (10%). In adjusted analysis, AD completion was more likely among persons who were older and had a history of malignancy or renal dysfunction. Age was the most powerful predictor of AD completion (60.7% completion in persons ≥80 years, 31.3% completion in persons 60–79 years, 13.6% completion in persons <60 years). Among the 164 persons dying after a median follow-up of 1.8 years, those having an AD specifying limits to care less frequently received mechanical ventilation in the last month of life (odds ratio [OR], 0.26; 95% confidence interval [CI], 0.07–0.88).Conclusion: The low use of AD among community-dwelling persons with HF is not surprising, considering that AD use is also low among persons with LV assist devices33 and critical or terminal illness.34 What is most noteworthy is the powerful effect of age on AD completion. Targeted efforts to increase AD use among younger patients with HF, therefore, seem to be particularly important, as this population experiences considerable morbidity and mortality despite its young age.1,35 Furthermore, additional attention should be directed to increasing the proportion of ADs with specific commentary on preferences for end-of-life care.36Predictors of Successful Cardiopulmonary ResuscitationWhat constitutes high-quality CPR remains elusive. Since CPR was first described more than half a century ago, it has undergone numerous modifications to become possibly too complex to teach to nonmedical personnel. In addition, resuscitation efforts represent tradeoffs in reality, for example, increased depth of compression often leads to reductions in the rate of compression, and the benefits derived from CPR are often nonlinear. For example, although public CPR campaigns have used the slogan “push hard and fast,” as the rate of chest compression surpasses a certain threshold, forward blood flow and cerebral perfusion pressure actually decrease. It has also been well documented that CPR performed in actuality fails to meet the quality standards proposed by guidelines even when performed by well-trained providers.37,38 Thus, the question is not only one of what is ideal but also what is feasible.In the following section, we review research aimed at improving survival after OHCA by examining the details of what constitutes quality CPR. We examine multiple tradeoffs including the pauses in chest compressions to administer defibrillation shocks39 and ventilation,40 details in chest compression rates and other specific measures,41,42 and assessment of new AEDs.43 Finally, we examine articles that weigh in on one of the largest debates in the past decade—forgoing ventilation rescue breaths by lay bystanders.44,45Chest Compression Alone Cardiopulmonary Resuscitation Is Associated With Better Long-Term Survival Compared With Standard Cardiopulmonary ResuscitationSummary: Authors compared dispatcher-assisted chest compression alone versus conventional CPR (chest compression interposed with rescue breathing) and its effect on long-term survival. This study used a retrospective cohort design, with patients combined from 2 randomized trials from 2004 to 2009—the Dispatch Assisted Resuscitation Trial (DART)46 and the Swedish Trial on Telephone Assisted CPR (TANGO)47—both of which compared survival to hospital discharge in patients >18 years of age with OHCA, and found no difference in outcome between the 2 types of CPR. The primary outcome in this combined study was long-term survival, obtained from the national/state death records through 2011. The Kaplan–Meier product limit method, in addition to Cox multivariable regression (adjusting for sociodemographics, initial rhythm, pathogenesis and location of arrest, witnessed status, and interval from call receipt to EMS arrival), was used to evaluate survival (at 1, 3, and 5 years) according to the type of CPR instruction. The final cohort consisted of 2496 participants (median age, 66 years), of whom 1243 (50%) were randomly assigned to chest compression alone and 1253 (50%) to conventional CPR. There were no significant differences in baseline factors between the 2 CPR groups. The study also reported 2260 deaths in long-term follow-up over 1153.2 person-years. Overall survival at 1, 3, and 5 years was 11%, 10.6%, and 9.4%, respectively. In the multivariate analysis, chest compression alone CPR was correlated with a significantly lower risk of death after adjustment for important confounders (adjusted HR, 0.91; 95% CI, 0.83–0.99; P=0.02).Conclusion: This study indicates that patients with OHCA receiving dispatcher-assisted chest compression alone CPR have a significantly better long-term survival than those with conventional CPR. These results support chest compression alone CPR to be considered the dominant approach for adult patients for whom dispatchers suspect cardiac arrest. Limitations include the fact that the individual trials were not designed to ascertain long-term outcomes or be combined; data were missing in functional status and quality of life, which are important outcomes in this patient population; and subjects with OHCA associated with trauma, asphyxia, and drowning were excluded and thus the results may not apply to these groups of patients.45Quantifying the Effect of Cardiopulmonary Resuscitation Quality on Cardiac Arrest Outcome: A Systematic Review and Meta-AnalysisSummary: The extent to which CPR quality affects survival in cardiac arrest remains poorly understood, and guidelines on chest compression rate, depth, and ventilation rate have been largely based on consensus.48,49 To measure the effects of CPR quality on cardiac arrest outcomes, investigators performed a systematic review and meta-analyses of clinical studies of CPR on adult patients with cardiac arrest in which survival was reported either as return of spontaneous circulation (ROSC) or survival to admission or discharge. Investigators identified 603 abstracts of which 10 studies met the inclusion criteria, representing 77 in-hospital and 1815 OHCA events. Estimates of survival rate were grouped by CPR metrics: chest compression rate, depth, no-flow fraction (time without chest compressions), and ventilation rate; the pooled effect was estimated by a random-effect model. Results showed that survival was significantly associated with deeper chest compressions, with a mean differences of 2.44 mm (95% CI, 1.19–3.69; P<0.001; n=6 studies; heterogeneity, I2=0.0%; P=0.9). No overall difference in mean chest compression rate between survivors and nonsurvivors was found. However, survival was correlated with chest compression rates closer to 85 to 100 compressions per minute (cpm; absolute mean difference from 85 cpm=−4.81 cpm; 95% CI, −8.19 to −1.43; P=0.005; absolute mean difference from 100 cpm=−5.04; 95% CI, −8.44 to −1.65; P=0.004; n=6 studies; heterogeneity, I2<49%; P>0.2). Neither no-flow fraction (n=7 studies) nor ventilation rate (n=4 studies) was significantly associated with changes in survival rates.Conclusion: This study found that only slightly deeper average chest compressions were associated with increased survival, but found no association with survival for no-flow fraction, ventilation rate, and mean chest compression rates. This last negative result may be because of the use of means and aggregation, which mask the minute-to-minute variations in resuscitation. Investigators used an additional approach to assess mean chest compression rate by comparing it against guidelines and found that a mean rate closer to the range established by guidelines was significantly correlated with survival. Unfortunately, the study is unable to assess whether the range proposed in guidelines represent an optimum. It also assumed that CPR metrics are independent, but in reality, increased rates of compression have been shown to be correlated with decreased depth.50 Despite these limitations, this study represents a key step in quantifying and specifying exactly which aspects of CPR are essential to improving survival—precisely because efforts in resuscitation are often a tradeoff among competing elements.42Relationship Between Chest Compression Rates and Outcomes From Cardiac ArrestSummary: Although current guidelines for CPR recommend chest compression