The state-of-the-science in cardiac care and resuscitation is constantly evolving. American Heart Association (AHA) resuscitation guidelines, clinical trials, prehospital protocol revisions, equipment innovations and recent research are changing the way we provide care in the field. More importantly, many new recommendations and studies are making an impact on our ability to improve resuscitation outcomes. This article will address several of the major impact areas.
The Importance of First Responder AED Use
Out-of-hospital cardiac arrest (OHCA) is one of this nation’s biggest public health concerns. Although the outcomes seen in patients with an initial rhythm of asystole or EMD/PEA continue to be poor despite recent advances in ACLS and post-arrest care, the potential for survival to hospital discharge in VF/VT arrests is much higher. However, time is of the essence. It is well known that there is a 5–10% decrease in survival for every minute delay in defibrillation in patients suffering from VF/VT cardiac arrest. That has generated a push for communities to increase the deployment of AEDs in the hopes that the public will more actively participate in the chain of survival and decrease the time to defibrillation.
Investigators from the Resuscitation Outcomes Consortium evaluated the potential survival benefit from AED application prior to EMS arrival.(1) Out of 13,769 patients, 289 had an AED applied prior to EMS arrival and survival was almost double with application of an AED. Although AEDs are extremely easy to use, the problem is that they are often not applied by the public even when readily accessible. A widespread study of first responder AED use was reported in a 2002 article published by Myerburg et al in which the impact of police vehicle deployment of AEDs was evaluated.(2) In that study, police were first to arrive at 56% of cardiac arrest calls for which a dual dispatch was initiated. Survival to hospital discharge was 17.2% in patients found to be in VF/VT in the police-AED program vs. just 9% in historical controls.
Out-of-hospital VF/VT arrests represent the group that stands to benefit the most from programs that increase awareness of cardiac arrest as well as the importance of bystander CPR and early defibrillation. Even though there is significant cost inherent to such a process, communities must continue to place AEDs in high-yield public locations and encourage public access defibrillation.
Optimal CPR & New Perspectives on Ventilations & Compressions
For many years, the concepts of “intubate, oxygenate and hyperventilate” were thought to be essential to maximizing survival from cardiac arrest. Securing the airway with an endotracheal tube along with aggressive ventilation with 100% oxygen were thought to be the key to performing expert CPR, while compressions were to be done as best as possible when not trying to intubate or defibrillate.
Similarly, giving mouth-to-mouth respirations to pulseless patients was thought to be “required” in order to help save a life before EMS arrived. Between the fear of not doing mouth to mouth correctly and concerns over patient regurgitation; contracting an infectious disease, such as hepatitis, TB or HIV; or not having a CPR card, most OHCAs did not receive bystander CPR.(3,4)
Much has changed as new results have shown that a simplified approach to both bystander- and EMS-provided CPR can dramatically improve survival of neurologically intact individuals. It is essential that all of us be expert in what works and what doesn’t if we are ever going to significantly improve our current overall CPR survival rate above 8%.(4)
What is now known is that compressions-only CPR works at least as well (if not better) as traditional compression and ventilation CPR. It is also very clear that performing compressions only, without devoting time and attention to ventilations, is much easier to teach and perform.(5,6)
In a recent study from Australia, lay rescuers were taught over the phone during an arrest to begin their resuscitation efforts with 400 compressions and their results were compared to a group receiving traditional CPR with both initial ventilations and compressions. Compressions-only CPR increased the likelihood of CPR being performed and also increased survival to hospital discharge in VF/VT patients by 40%, from 21% to 29%.(7)
This protocol, which is now advocated by the Medical Priority Dispatch System (MPDS), does recommend ventilation begin at a ratio of 2 per 100 compressions, but only after four minutes of compressions.
Additional support for doing compressions-only CPR comes from the SOS-KANTO trial, where good neurologic outcome was 2.7 times more likely if ventilations were withheld.(8)
Although there is now general agreement that compressions-only CPR is optimal for the general public, how EMS should initially perform CPR is more controversial. Services that follow traditional practices of early ventilation and intubation for victims of cardiac arrest should carefully consider whether this is still appropriate, especially in patients with shockable rhythms.
An important study appeared in 2009 from the Tucson and Phoenix Fire Departments that compared two methods of ventilation in more than 1,000 cardiac arrest patients.(9) Patients either received slow bag-valve mask ventilations or passive oxygenation with just a non-rebreather face mask applied. In those patients with witnessed VF/VT, passive oxygenation improved survival by about 50%; unfortunately, no survival benefits were seen in un-witnessed arrests or patients with non-shockable rhythms.
The benefits of not providing early ventilation appear two-fold: First, not ventilating avoids the resultant rises in intrathoracic pressure that might impede venous return, thus no ventilations have the potential to increase cardiac output. Second, by focusing on compressions only, rescuers can increase the percent of time they are on the chest performing compressions. This chest compression fraction must be maximized in order to optimize survival.(10)
Although it’s clear that compressions should be begun immediately post arrest, and that ventilations need not begin immediately, two other issues are yet to be resolved: (1) whether patients in VF/VT should be defibrillated as soon as possible or receive compressions for 2–4 minutes pre-shock and (2) whether cardiac arrest patients should be endotracheally intubated at the scene.
An immediate shock is indicated in witnessed arrests, and those in which the downtime is less than 4–5 minutes.(11–13) Some have suggested in those patients with unwitnessed arrests, which are likely in excess of 4–5 minutes, compressions-only CPR for 2–3 minutes may improve survival.(12,13) This is because in patients with prolonged downtimes, compressions may circulate oxygenated blood through the coronary arteries and mitigate some of the anaerobic metabolic derangements of prolonged pulselessness.
However, both a recent study and Cochrane Database Systematic Review have shown that delayed defibrillation has no advantage to immediate defibrillation.(14,15)
Thus, we endorse a single, simple protocol that focuses on rhythm analysis and defibrillation as soon as possible. This is more easily taught and implanted rather than one that requires judgment and an estimation of downtime.
EMS must also make informed decisions on how to manage an airway once ventilations are begun. It is no longer universally accepted that early endotracheal intubation optimizes survival in cardiac arrest patients.
In an analysis of all the available literature up to 2009, the Cochrane Collaboration, concluded that “in non-traumatic cardiac arrest, it is unlikely that intubation carries the same life saving benefit as early defibrillation and bystander cardiopulmonary resuscitation.”(16)
Multiple retrospective studies comparing routine ETI vs. either bag mask ventilation or early use of a supraglottic airway, such as a Combitube or King Airway, have demonstrated increased survival with delayed or no attempted intubation.(16–20)
A recent study from the Mecklenburg (N.C.) EMS System showed that using a King LT-D supraglottic airway resulted in a significantly higher first attempt success rate when compared to trying to insert an endotracheal tube.(21)
There are many reasons why definitely securing the airway with an endotracheal tube may not be optimal in the early phases of an attempted cardiac resuscitation. First, compressions may be interrupted when ETI is attempted. Other reasons include increased potential for hyperventilation, inadvertent esophageal intubation and difficulty intubating, which may delay other therapies and compromise or interrupt compressions.(22)
Thus, supraglotic airways (SGAs) offer many potential benefits over endotracheal intubation. They can be inserted faster, do not require visualizing the trachea, do not interrupt CPR and have a much higher degree of first pass success.(23)
However, very recent evidence is casting doubt on the potential superiority of SGAs. In a retrospective evaluation of an ROC study involving more than 10,000 patients, ETI improved survival to discharge when compared to SGAs (4.7% vs. 3.9%; OR: 1.40).(24) The reasons for decreased survival from the supragolottic devices are unclear, but in another recent publication these devices were shown to decrease carotid blood flow in an animal study.(25)
At the present time, the best way to initially manage an airway in cardiac arrest is unclear. What is clear is that, if ETI is an EMS agency’s initial airway of choice, it is essential that paramedics be truly expert at this skill, practice often, be prepared for difficult airways, perform this skill rapidly with minimal interference to compressing the chest, and don’t hyperventilate patients once they are successfully intubated.
Agencies should carefully consider whether bag-valve ventilation or using an SGA may be more appropriate than requiring ETI to be the preferred airway of choice.
While ALS continues to be part of the AHA/ECC chain of survival, its effect on survival to hospital discharge has come into question. To that end, the 2010 AHA Guidelines de-emphasized IV access and drug delivery. This stance is supported by the lack of evidence demonstrating increase in survival to hospital discharge with administration of vasoactive medications and antiarrhythmics in the field.
There is also concern with the use of epinephrine because it may have deleterious effects on cerebral microcirculation and post-arrest myocardial function. Multiple studies have attempted to address the issue of the role of epinephrine and other ACLS drugs in cardiac arrest and their impact on patient survival.
In 2009, Lars Wik and colleagues randomized patients with out-of-hospital cardiac arrest to ACLS with and without access to IV drug administration.(26) Their results demonstrated an increase in ROSC with IV drug administration (40% vs. 25%), but not a statistically different difference in survival to hospital discharge (10.5% vs. 9.2%). Thus they found no long-term benefit to ACLS drugs.
Similar results were recently published in a large study from Japan involving almost 500,000 patients, 15,000 of which received epinephrine.27 Although there was a dramatic improvement of ROSC with epinephrine (18.5% vs. only 5.7% without epinephrine), the one-month survival data was quite different. At one month, those receiving epinephrine fared much worse and were less likely to be alive or alive with good neurologic function (5.1% with epinephrine vs. 7.0% without; and 1.3% vs. 3.1% respectively for good neuro outcomes). These deleterious effects were seen in patients with VF/VT or a nonshockable rhythm.
Atropine’s role in cardiac arrest has also been recently evaluated, and like the epinephrine studies cited above, has yielded very surprising results. The SOS-KANTO Trial studied 7,448 patients to compare the effect of epinephrine plus atropine vs. epinephrine alone in patients with either asystole or PEA.(28)
Atropine improved ROSC in both rhythms and did not affect the 30-day survival of patients with asystole. However, at 30 days, those patients who received atropine plus epinephrine had decreased survival as compared to those who received epinephrine alone (3.2% vs. 7.1%), and of the survivors, atropine decreased the likelihood of good neuro survival (0.59% vs. 1.02%).
Other studies have shown similar findings with the use of epinephrine.(29,30) Similar to adrenaline, there is insufficient data demonstrating improvement in survival to hospital discharge with the use of vasopressin, lidocaine and amiodarone.
It is important to recognize that as post-arrest care improves with the implementation of therapeutic hypothermia and transport to PCI-capable centers, increases in the rate of ROSC with the use of epinephrine and antiarrhythmics in the field could potentially translate into improvement in survival to hospital discharge. It is clear, however, that a focus on obtaining IV access and administering ACLS medications cannot trump initiation of other lifesaving measures.
ACLS will continue to be part of OOH cardiac arrest resuscitation, however, at this time, given the lack of good evidence demonstrating clear benefit with the routine use of IV medications in the field, services must focus on interventions that have proven efficacy, such as good CPR, early defibrillation and coordinated post-arrest care with transport to resuscitation centers that can provide both therapeutic hypothermia and early cardiac catheterization.
Methods to Avoid Hyperventilation & Maximize Compressions
Recent CPR research has focused on developing technology that will assist providers in delivering optimal CPR to ensure the best possible chance of ROSC followed by transport to a resuscitation center able to continue post-arrest care.
The importance of providing more than 80 compressions per minute has been noted in animal studies as well as many clinical observations.(31,32)
In addition, evidence suggests that excessive positive pressure ventilation and hyperventilation during CPR can be detrimental to resuscitation hemodynamics and outcomes in patients suffering from cardiac arrest.(33,34)
Metronomes are relatively inexpensive, are available on some cardiac monitor/defibrillators, and can provide EMTs and paramedics with much-needed feedback to stay on target with compression and ventilation rates.
A 2010 study that looked at the use of an audible metronome for guiding chest compressions rate demonstrated that metronomes are beneficial in improving the rate and effectiveness of chest compressions.(35–45) (For more information on metronome use in CPR, see p. 8 of this supplement.) A 2009 study found that a combination tock (sound) and voice-prompting metronome was effective at directing correct chest compression and ventilation rates both before and after intubation.(46)
For this study, 68 ﬁreﬁghter EMTs from the Spokane (Wash.) Fire Department and Spokane Valley Fire Department participated in pairs, 17 pairs for the intervention (CPR metronome) group and 17 pairs for the control group. Each pair performed two CPR sessions, switching roles between sessions, resulting in 34 CPR sessions for each group.
This was the first study to methodically evaluate metronome guidance of both chest compressions and ventilation, both before and after endotracheal intubation. The combined tone and voice prompt audio guidance was effective at maintaining the target chest compression rate and avoiding the common problem of hyperventilation during CPR by professional rescuers.(37,47,48)
Without any audible guidance, chest compressions rates varied widely, from 75–160 per minute. Without metronome guidance, 29 out of 34 (85%) of the professional rescuer pairs performed chest compressions outside the range of 90–110 compressions per minute, and 24 out of 34 (71%) were outside the broader range of 90–120 compressions per minute proposed as a target by Kramer-Johansen et al.(49) Of note, the majority of those compression rates outside the range were above 120 per minute.
Too slow a rate delivers too few compressions per minute to achieve optimal resuscitation haemodynamics and outcomes.(50,51) At the time of this 2010 study, it was assumed that too fast a compression rate is less harmful than too slow, but both extremes can be problematic. We now know from the Idris study (see p. 4) that very fast compression rates (greater than 125/minute) can compromise coronary blood ﬂow due to a signiﬁcant shortening of the diastolic period when the majority of coronary ﬂow occurs.(52)
In one of the largest studies, Kern et al discovered that without the metronome device, only 15% of pre-hospital providers achieved an appropriate compression and ventilation rate. However, with the utilization of the audible metronome, 100% of the caregivers provided appropriate compressions as well as avoided hyperventilation.(53)
The need and role for patient ventilation during resuscitation has also been dramatically re-thought during the last decade. Some believe minimal or no positive pressure ventilation should be provided during the early resuscitation efforts.35,54–56 Many believe hyperventilation during resuscitation is particularly harmful.(47,57)
Most researchers and clinicians appear to agree that some source of re-oxygenation and ventilation (be it positive pressure techniques or passive oxygen insufﬂation delivered by a device such as a high concentration oxygen mask and bag, combined with chest compressions) is important sometime in the rescue protocol.
The major issue is how to provide oxygenation and adequate ventilation without the deleterious effect on haemodynamics associated with over-ventilating during the low ﬂow state of CPR.
Hyperventilation is common during in-hospital and out-of-hospital treatment of cardiac arrest. A 2005 study at the University of Chicago Hospitals reported that in a series of 67 patients, the ventilation rate exceeded 20/min (−1) in 59% of the CPR periods.(48)
University of Wisconsin investigators studied the number of breaths provided by professional EMS rescuers responding to cardiac arrests in their communities. Remarkably, they found that their professional EMS personnel provided 37±4 breaths/minute, with a range of 19–49 minute (−1).(47)
Recognizing this as a potentially major problem, extensive re-training was conducted emphasizing the importance of no more than 10–12 breaths/minute. A second period of observation of actual EMS performance was then carried out and revealed an average ventilation rate (after re-training) of 22±3 breaths/minute, with a range of 15–31/minute. No patient in that follow-up series received ventilations at ≤12 breaths/minute.
In accompanying laboratory experiments to this clinical observation, the Chicago investigators found that hyperventilation lowered coronary perfusion pressure during CPR, and that one-hour survival was less among the subjects receiving hyperventilation during their resuscitation.(47)
Another metronome study showed that a combined chest compression and ventilation audible metronome can avoid hyperventilation by professional EMS providers using an advanced airway (after endotracheal intubation). Without the metronome guidance, the mean ventilation rate was 10 (±4) (median = 10), with a range of 6–25 breaths per minute. However, sometime during their simulated rescue, 11 out of the 34 (32%) were hyperventilated. When the metronome was utilized, there was no difference in the mean or median ventilation rates (10±0, median = 10), and none were hyperventilated (0/34).(46)
Whereas the metronome provides a guided means for rescuers to perform manual chest compressions, there is increasing interest in mechanical compression devices that deliver the appropriate and consistent depth, rate and recoil necessary, thus “freeing” responders to perform other critical tasks during the resuscitation. Initial concerns with the use of these mechanical delivery systems were their cost as well as the amount of “time off the chest” while applying the device to the patient.
The early research was quite promising regarding the benefit of these devices. Ong and Ornato et al performed an analysis of more than 700 adults with non-traumatic OHCA and found that compared to manual CPR, a resuscitation strategy using a load-distributing band chest compression device improved survival to hospital discharge.(58)
Conversely, in the same journal, Hallstrom and Rea performed a multicenter randomized trial of automated compression devices and concluded that patients receiving this therapy suffered worse neurologic outcomes and a trend toward worse survival as compared to manual CPR.(59) These competing conclusions on such devices resulted in a dramatic increase in their study and improvement.
As technology advances and more studies are conducted, these devices may pave the way for improved survival with neurologic function post-cardiac arrest. For more information on mechanical CPR, see “The Merits of Mechanical CPR” on p. 24 of this supplement.
The use of an impedance threshold device (ITD), also referred to as the ResQPOD, as a circulatory adjunct during CPR has become more common in the prehospital care of the cardiac arrest victim. The purpose of the ITD is to impede the return of respiratory gases into the chest selectively during the recoil phase of CPR, thus enhancing negative intrathoracic pressure and improving blood pressure and cardiac output. It also contains timing assist lights, which may be turned on to provide guidance on proper chest compression and ventilation rates.(60)
Pirallo et al initially studied this device and found that as compared to a “sham” device, the ITD was safe and improved blood pressure in arrest victims.(61) This promising study led to further investigation into the use of the ITD as a standard adjunct to traditional CPR and some believe that this device may dramatically increase survival from OHCA.
However, a very large trial (ROC PRIMED) which further analyzed the ITD was conducted at 10 locations across the U.S. and Canada and involved more than 20,000 EMS providers. Unfortunately, the Data and Safety Monitoring Board recommended that the study end enrollment and terminate early because the ITD use was showing no improvement in patient survival rates (it did not show a decrease in survival rate).(62)
Despite the results of this one study, many EMS systems have used, and continue to use, the ITD along with other important resuscitation components and are experiencing increased resuscitation results.
A 2009 observational time series study in Wake County, N.C., involved 1,365 patients and measured survival to hospital discharge in patients with OHCA during a tiered implementation of the 2005 AHA Guidelines. This urban/suburban EMS system, which responded to 65,000 calls, including 700 cardiac arrests at the time of the study, was able to double survival between the pre- and post-implementation phases by implementation of a community-wide focus on resuscitation and the sequential implementation of 2005 AHA Guidelines for compressions, ventilations and induced hypothermia.
The 46-month study focused on results of using dispatcher-assisted CPR instructions (MPDS), dispatch of ALS units, a fire department first-responder apparatus and a paramedic supervisor vehicle for presumed cardiac arrests; automated defibrillators reprogrammed to deliver a single shock that delivered the highest energy level available for each shock rather than a “stacked” sequence (up to three shocks); paramedic crews manually delivering a “stacked” sequence of up to three shocks without interposed chest compressions; minimal interruption of chest compressions; use of intraosseous infusion (EZ-IO), therapeutic hypothermia and the ResQPOD ITD; control of ventilation rates guided by a timing light on the ResQPOD; and the concept of working cardiac arrests in the field until ROSC or obvious futility.(63)
Note: For an additional study, “Intraosseous Infusion Proven Effective in Therapeutic Hypothermia,” sponsored by Vidacare, go to www.jems.com/article/patient-care/io-in-th-web-bonus.
Aufderheide et al compared the use of an ITD with Active Compression Decompression CPR (ACD-CPR) in the ResQTRIAL. This was a multicenter, prospective, randomized, prehospital clinical trial that compared an ITD (ResQPOD) and ACD-CPR Device (ResQPUMP) to conventional CPR in more than 1,600 patients.64
For patients with cardiac etiologies, the combination of ACD-CPR with an ITD resulted in a 53% increase (5.8% to 8.9%) in survival to hospital discharge with favorable neurologic function and a survival benefit of 49% persisted to one year. This study builds on 22 animal and four human trials previously demonstrating positive hemodynamic and survival benefits when ACD-CPR is combined with an ITD.
Transportation of Patients with ROSC to Resuscitation Centers
Post-arrest cardiac care was one of the most notable sections of the 2010 AHA Guidelines. The guidelines note that organized post-arrest care with an emphasis on multidisciplinary programs that focus on optimizing hemodynamic, neurologic and metabolic function (including therapeutic hypothermia) may improve survival to hospital discharge among victims who achieve ROSC following cardiac arrest either in- or out-of-hospital.
Although it is not yet possible to determine the individual effect of many of these therapies, when bundled as an integrated system of care, their deployment appears to improve outcomes.65 This is a strong statement that lends support for standard EMS protocols that deem that post-cardiac arrest patients who have successfully received ROSC in the field be transported to a center capable of providing intensive post-resuscitative care (angiography and hypothermia) despite bypassing a closer facility. Recent evidence firmly establishes that hospitals that do provide early coronary angiography as well as controlled hypothermia can improve patient survival and neurologic outcomes, specifically if the initial rhythm is VF.
In Seattle, researchers retrospectively studied 491 consecutive adult patients with out-of-hospital, non-traumatic cardiac arrest who presented before and after a protocol for hypothermia was instituted.66 These patients all had ROSC and various initial rhythms (asystole, PEA, VF/VT). The researchers concluded that a ventricular fibrillation arrest victim who was then cooled after ROSC had an almost two-fold increase in neurologically intact discharge from the hospital. This did not hold true for other presenting arrhythmias.
Similar results were found in an Australian study of more than 100 cardiac arrest victims where therapeutic hypothermia and early coronary angiography dramatically improved neurologically intact survival to hospital discharge (64% vs. 39%).(67)
Given such statistics as these, the U.S. Metropolitan Municipalities EMS Medical Directors (“Eagles”) Consortium endorsed transportation of patients to resuscitation centers, noting that it is not feasible for many hospitals to make the commitment to care for large numbers of critically ill patients and the accompanying investigational activities, whether in the prehospital, ED or inpatient arenas.(68)
While much has been done, and continues to be accomplished in the area of patient resuscitation, we must continue to research, innovate and implement processes and procedures to improve our resuscitation of patients. The old “mold” and methods may need to be replaced by new protocols, equipment, staffing and response models and transportation (and non-transport) of patients.
Corey M. Slovis, MD, FACEP, is professor of emergency medicine and medicine, and chairman of the Department of Emergency Medicine at Vanderbilt University Medical Center in Nashville, Tenn. Dr. Slovis’ responsibilities center on his roles as chief of emergency services at Vanderbilt and serving as the medical director for Metro Nashville’s Fire Department and Nashville International Airport. Dr. Slovis is a member of the JEMS Editorial Board and a nationally renowned instructor.
Disclosure: The author has reported no conflicts of interest with the sponsors of this supplement.
Jared J. McKinney, MD, is assistant professor of emergency medicine at Vanderbilt University Medical Center in Nashville, Tenn., and assistant medical director for Metro Nashville Fire Department. He was recently named director of LifeFlight Event Medicine and chairman of the Vanderbilt Resuscitation Committee. Dr. McKinney earned an undergraduate degree from Purdue University in engineering and graduated from Vanderbilt University’s School of Medicine. During his residency he was presented with the Ian D. Jones Chief Resident’s Award. He is a member of the Tennessee D-MAT team and was deployed to Louisiana following Hurricane Gustav in 2008.
Disclosure: The author has reported no conflicts of interest with the sponsors of this supplement.
Jeremy Brywczynski, MD, is assistant professor of emergency medicine at Vanderbilt University Medical Center, assistant medical director of Metro Nashville Fire Department, and medical director of Vanderbilt LifeFlight. He graduated Magna Cum Laude from the University of Dayton with a degree in biology and earned his medical degree from Wright State Boonshoft School of Medicine in Fairborn, Ohio, completing a residency in emergency medicine as well as a fellowship in EMS at Vanderbilt University.
Disclosure: The author has reported no conflicts of interest with the sponsors of this supplement.
A.J. Heightman, MPA, EMT-P is the editor-in-chief of JEMS. He is a former EMS director and EMS operations director who has been involved in EMS systems development for 40 years.
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