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In October of 2015, the American Heart Association released the 2015 American Heart Association (AHA) Guidelines Update for Cardiopulmonary Resuscitation (CPR) and Emergency Cardiovascular Care (ECC). This publication represents the most current recommendations for improving survival from cardiac arrest. In many cases, the AHA did not significantly change previous recommendations but simply clarified meanings. However, in other cases, the AHA made recommendations that did not previously exist.
Chain of Survival: Affirmed yet revised
The AHA continues to recognize the relevancy of the Chain of Survival; however, it recognizes the important differences between responding to a cardiac arrest in the out-of-hospital (OOH) environment and responding to an arrest that occurs inside the hospital. The role of the lay rescuer is significantly more important in the OOH setting where, ideally the patient receives CPR and defibrillation before the EMS team arrives on the scene. Without those early interventions, the chances of survival decrease.
Although early CPR and defibrillation still have value for cardiac arrest occurring in the in-hospital setting, those initial responders are often health care providers with some degree of professional training. In many of these cases, patients display clear warning signs of impending cardiac arrest. Prompt recognition of those warning signs and appropriate intervention could possibly prevent the cardiac arrest from occurring in the first place.
Multiple studies since the release of the 2010 AHA Guidelines demonstrate a decrease in the incidence of in-hospital cardiac arrest when hospitals implemented a system of medical emergency team (MET) responses to patients with signs of impending cardiac arrest [1-10]. Thus, the 2015 recommendation is for hospitals to implement MET responses based on early warning signs.
In the OOH environment, the emergency medical dispatcher (EMD) plays a key role in the chain of survival once the bystander accesses the EMS system. The AHA states that after identification of an unconscious adult patient with abnormal or absent breathing, it is reasonable for the EMD to assume the patient is in cardiac arrest. The recommendation is for the EMD to provide compression-only instruction until EMS arrival.
Resuscitation: A concerted effort
Most of the sequential assessments and actions for CPR remain unchanged from the 2010 recommendations. Although one of the limitations of any patient care algorithm is the linear presentation of the steps, the AHA acknowledges that EMS responses rarely involve a single person. A team of responders can therefore accomplish multiple tasks simultaneously.
Approach the victim cautiously, making sure the scene is safe before proceeding. Upon contact with the victim, verify unresponsiveness and send someone to get an AED or manual defibrillator. Determine whether the patient is breathing normally. Unresponsive patients who are not breathing normally have a high likelihood of being in cardiac arrest [11-19].
Do not confuse gasping with normal breathing. Gasping occurs frequently in patients who develop sudden cardiac arrest, but rapidly disappears as time progresses. In one study, EMS responders witnessed gasping in about 20 percent of patients when the EMS response time was less than seven minutes . However, when the EMS response time was greater than nine minutes, only 7 percent of the patients were still gasping. Gasping is associated with increased survival to discharge rates .
Simultaneously during the breathing assessment, check the patient's carotid artery to verify pulselessness. Because health care providers often have difficulty determining whether a pulse is present [22-28], withhold chest compressions only when absolutely sure the pulse is present. In many instances, health care providers also take too long to make a decision [22,25]. Do not spend more than 10 seconds checking for a pulse. If the pulse is absent or you are unsure if the pulse is present, begin chest compressions.
Chest compression recommendations
The original recommendation for where to place the hands when performing chest compressions comes from canine studies extrapolated to humans . Over the years, recommendations for hand positioning when performing chest compressions have migrated from two fingers above the tip of the xiphoid process to the lower half of the breastbone. Two studies since the 2010 AHA Guidelines failed to identify an optimal alternative hand placement position for closed chest massage in adults [30,31]. Therefore, the 2015 Guidelines do not change hand placement recommendations made in 2010.
The original recommendation for chest compression depth in the average adult called for the rescuer to push the sternum to a depth of 3 or 4 centimeters (about 1.0 - 1.5 inches) towards the vertebral column . Since that original recommendation, researchers have searched for the optimal chest compression depth. In the 2010, the AHA recommended a chest compression depth greater than previously recommended . Although more recent evidence does not contradict this statement [33-36], there is some evidence to suggest that compression depths greater than 2.4 inches may result in an increase in patient injuries .
In response the AHA now recommends that health care providers compress the chest to a depth of at least two inches, but no deeper than 2.4 inches. In order to hit this narrow target, the AHA recommends the use of audiovisual feedback devices that allow real time corrections to poor compression technique.
After compressing to the proper depth, the AHA recommends health care providers allow full recoil of the chest before delivering the next compression (32). Animal studies suggest that incomplete recoil, also known as rescuer leaning, can negatively impact cerebral and coronary perfusion [38-41]. Other studies suggest leaning is common among health care providers [42-45]. So, despite the lack of conclusive evidence associating leaning with worsened clinical outcomes, the AHA recommends health care providers avoid leaning on the patient's chest while performing chest compressions.
One important determinate of Return of Spontaneous Circulation (ROSC) and neurologically intact survival is the actual number of chest compressions health care providers deliver to the patient during each minute of the resuscitation period [46,47]. An in-hospital study demonstrated improved outcomes with the delivery of 80 chest compressions per minute (46) and an out-of-hospital observational study found improved outcomes when EMS personnel delivered 68-89 compressions per minute (47). To compensate for the compression interruptions that occur with defibrillation attempts, ventilation, or to switch chest compressors, the 2010 Guidelines recommended a chest compression rate of at least 100 compressions per minute .
Although this recommendation clarifies the minimum number chest compressions per minute, the recommendation did not indicate a maximum number of compressions beyond which survival outcomes could be negatively affected. Since 2010, two studies suggest the optimal chest compression rate likely lies between 100 and 120 chest compressions per minute [48,49]. This forms the bases for the 2015 recommendation.
The 2015 Guidelines also includes a recommendation to continue to provide 30 chest compressions followed immediately by two ventilations. This recommendation remains unchanged from the 2010 Guidelines and is based on consensus opinion rather than definitive evidence .
All about the beat
A caveat to the standard 30:2 compression ventilation ratio is that rescuers must minimize interruptions in chest compressions. This is true for both the potentially therapeutic pauses that accompany ventilation and defibrillation, and the non-therapeutic pauses, such as moving the patient to the ambulance. To illustrate the importance of minimizing interruptions, the AHA defined a new metric, chest compression fraction (CCF), that did not exist in 2010.
The CCF represents the proportion of time during the resuscitation attempt that someone is actually pushing on the patient's chest . Minimizing interruptions in chest compressions allows rescuers to spend more time compressing the sternum, which results in higher CCF. Higher CCF increases the likelihood of survival [47,50]. Although an expert panel consensus found a CCF of 80 percent achievable , the 2015 recommendation calls for rescue teams to achieve a CCF of at least 60 percent.
An alternative to the standard 30:2 compression/ventilation ratio gaining traction in the out-of-hospital environment is a continuous chest compression model, either with active asynchronous ventilation delivered without interrupting compressions or with passive ventilation in the early stages of the resuscitation attempt.
The 2010 Guidelines recommended asynchronous ventilation with continuous chest compression, but only after the insertion of an advanced airway . A newborn manikin model of cardiac arrest demonstrated higher minute ventilation when breaths were delivered asynchronously via bag-mask with continuous chest compressions compared to coordinated ventilations and compressions .
Animal studies of asynchronous ventilation during continuous chest compression could find no difference in outcome compared to standard CPR [53,54]. A recent large cluster-randomized trial with crossover involving more than 23,700 patients suffering OOH cardiac arrest could find no survival advantages associated with continuous chest compressions and asynchronous ventilation compared to standard CPR .
In the passive ventilation approach, EMS providers generally deliver three cycles of 200 continuous chest compressions with a rhythm analysis and defibrillation attempt after every two hundred compressions and ventilation occurs passively through elastic recoil of the patient's chest [56-60]. In many of the agencies, rescuers maintain airway patency with an oropharyngeal airway and then place an oxygen mask over the patient's face to allow passive oxygen delivery . Despite the fact that some suggest that passive ventilation created by compression only CPR cannot generate tidal volumes adequate for effective gas exchange [61,62], the 2015 Guidelines considers continuous chest compression with delayed ventilation to be a reasonable approach to the early management of a witnessed OOH arrest with a presenting rhythm of ventricular fibrillation or pulseless ventricular tachycardia (VF/pVT).
In the first published report on the use of passive oxygen insufflation in the management of OOH cardiac arrest, researchers found lower arterial carbon dioxide partial pressures and higher pH and partial pressure of arterial oxygen in the passively ventilated patients compared to the patients receiving traditional ventilation . Subsequently, in a larger study of OOH cardiac arrest, researchers could not find a difference in ROSC, survival to hospital admission, or survival to ICU discharge rate between patients passively oxygenated and those receiving conventional oxygenation and ventilation techniques .
However, in both of these studies, passive insufflation occurred through specially modified endotracheal tubes thereby limiting generalization of the results to passive insufflation through an oxygen mask. A retrospective analysis of a statewide OOH cardiac arrest database found that passive ventilation using an OPA and an oxygen mask improved neurologically intact survival after witnessed VF/pVT when compared to bag-valve-mask ventilation . For unwitnessed VF/pVT and non-shockable rhythms, survival was similar. Until more clinical data is available, the AHA does not recommend the routine use of passive ventilation during conventional CPR.
Another strategy common in the EMS environment is to deliver a period of CPR, typically 1.5 – 3 minutes, before administering a defibrillation attempt. This approach is colloquially known as priming the pump. Twelve studies of varying complexity have failed to show any outcome advantages offered by up to 180 seconds of chest compressions before delivery of the first defibrillation attempt [65-76]. For patients being monitored, defibrillate as quickly as possible after the patient develops VF/pVT. For patients in cardiac arrest who are not being monitored, perform CPR while someone retrieves the defibrillator and applies the pads. As soon as the defibrillator is ready, deliver a shock and resume CPR beginning with chest compressions.
Naloxone administration recommendations
In 2014, the U. S. Food and Drug Administration approved for sale a naloxone autoinjector for use by the general public . Almost immediately, the AHA Training Network asked for guidance on how to incorporate this device into current training programs. The International Liaison Committee on Resuscitation (ILCOR) attempted to review research relevant to the question of whether naloxone administration to patients suspected of having opioid toxicity in addition to CPR provided any survival benefits compared to standard CPR alone but could not find any .
Despite the lack of evidence, the consensus opinion was that it is reasonable for appropriately trained health care providers to administer intramuscular or intranasal naloxone to patients who are not breathing normally and are suspected of overdosing on opioids. For patients in cardiac arrest with a known or suspected opioid overdose, health care providers can consider administering naloxone, but only after initiating CPR.
Oxygen – how much?
Over the past few years, researchers and clinicians began questioning the value of administering high-concentration oxygen to patients who suffer cardiac arrest, especially once the patient achieves ROSC. An observational OOH cardiac arrest study utilizing high-concentration oxygen administration during the resuscitation period found that increases in PaO2 levels correlated with increased rate of survival to hospital admission with a non-significant trend toward improved neurological outcome . On the other hand, several studies have demonstrated increased mortality and poor neurologic status associated with higher levels of the maximum measured PaO2 during the post-resuscitation period [80-83]. Other studies have been unable to demonstrate this harm [84-88].
Thus, the AHA recommends that EMS providers deliver high-concentration oxygen via bag-mask during the resuscitation attempt when CPR is in progress. However, once the patient achieves ROSC and the health care team can reliably measure oxyhemoglobin saturation, the AHA states it is reasonable to titrate oxygen delivery to achieve a saturation value of at least 94 percent.
Advanced airway recommendations
At the advanced level, one issue that remains controversial is whether EMS personnel should insert an advanced airway during the resuscitation attempt. Although many studies demonstrate worsened outcomes with ventilation through an advanced airway compared to bag-mask ventilation [89-95], the results of these studies may actually demonstrate the effects of other variables rather than the type of airway used. For example, patients who do not respond to CPR and the initial defibrillation attempt likely have more profound metabolic derangements than those who respond early. The AHA recommends EMS personnel provide oxygenation and ventilation with either a bag mask or with an advanced airway. The decision on what specific advanced airway (endotracheal or supraglottic) should be based on the training and skill level of the responders. There are no recommendations on the optimal timing for the insertion.
Vasopressor use during cardiac arrest
Another controversial subject is whether the administration of vasopressors during the resuscitation attempt offers any survival advantages for the patient. Since 2010, one randomized control trial (RCT)  and one large observational trial  found patients who received epinephrine were more likely to achieve ROSC in the field compared to patients who did not received epinephrine. However, the RCT study was stopped early and was therefore unable to evaluate whether epinephrine provided any long-term survival advantages. The observational trial found that epinephrine administration was associated with a decreased chance of survival to one-month after discharge with good functional outcome.
Another observational trial could not demonstrate any improvements in ROSC, survival to hospital admission, survival to hospital discharge, or good neurological recovery .
The only study to compare exclusive vasopressin administration to exclusive epinephrine administration could find no differences in the rates of ROSC, 24-hour survival or survival to hospital discharge between the two groups .
Another study randomized patients to receive either vasopressin to epinephrine . If the patients did not respond to the initial drug, all patients received epinephrine from that point forward. Adding vasopressin to the standard management of cardiac arrest did not improve survival to hospital discharge rates.
As a result, the AHA continues to recommend epinephrine as the vasopressor of choice for the management of cardiac arrest. The AHA has removed vasopressin from the cardiac arrest algorithm.
When to administer epinephrine?
Now that the AHA has simplified the cardiac arrest algorithm by removing one of the vasopressors, one should consider the issue of timing. The 2010 Guidelines recommended vasopressor administration after the second defibrillation attempt for shock-refractory rhythms. Without any new evidence to support a change, the AHA continues to recommend that strategy for shockable rhythms.
However, the recommendation for when to administer the first dose of epinephrine in non-shockable rhythms is different. Three studies suggest improved outcomes with earlier (rather than later or not at all) administration of epinephrine (101-103). Thus, after initiating CPR, it is reasonable for EMS providers to administer epinephrine as early as possible when patients are in a non-shockable rhythm.
The other group of medications routinely administered during a resuscitation attempt is the antiarrhythmics. Two trials demonstrated that amiodarone provided short-term survival advantages compared to lidocaine in patients who suffered an OOH cardiac arrest and presented in Vf/pVT [104-105]. Amiodarone continues to be the recommended first-line antiarrhythmic agent in shock refractory cardiac arrest rhythms. Lidocaine remains an acceptable alternative. For patients with hypomagnesemia or torsades do pointes, the AHA recommends substituting magnesium sulfate for amiodarone.
Corticosteroid use in cardiac arrest
It is worth mentioning a recommendation that applies exclusively to the in-hospital environment. An animal study demonstrated that corticosteroid administration reverses the vasopressin hyporesponsiveness often seen in septic shock . In vitro studies of human arteries found that corticosteroid administration inhibits the endotoxin-mediated contractile depression response to norepinephrine during septic shock . Other researchers have demonstrated that cardiac arrest produces a sepsis-like syndrome during the post-resuscitation period  leading to speculation that corticosteroids may enhance the cardiovascular effects of epinephrine and result in higher survival rates following cardiac arrest .
A small RCT of OOH cardiac arrest could not demonstrate any survival advantages associated with corticosteroid administration . In a small prospective, non-randomized trial, patients arriving in the emergency department with CPR in progress received either a corticosteroid during the resuscitation attempt or an injection of plain saline . Patients who received the corticosteroid had significantly higher ROSC rates compared to those who received the plain saline. Moreover, if the corticosteroid was administered within six minutes of the patient's arrival in the emergency department, the difference in ROSC rates was even more striking. However, there was no difference in survival to hospital discharge or 1- and 7-day survival rates between the two groups. The exact role of steroids in the management of OOH cardiac arrest remains unclear.
However, for patients who develop cardiac arrest as an in-patient in the hospital, two RCTs found improved survival to hospital discharge associated with the administration of a combination of vasopressin, epinephrine, and methylprednisolone administered after achieving ROSC if the patient developed shock [112,113]. Although the AHA does not recommend this drug combination for OOH resuscitation, hospital personnel may consider administering the drugs.
EMS personnel should continue to place a high priority on identifying and correcting hypotension (defined as a systolic blood pressure less than 90 mm Hg or a mean arterial pressure (MAP) less than 65 mm Hg) during the post cardiac arrest phase. During the period, if the rescue team can reliably measure oxyhemoglobin saturation, the team can begin titrating oxygen administration to achieve a saturation value of at least 94 percent.
The use of antiarrhythmic infusions
For patients who achieve ROSC after presenting in a shockable rhythm, many EMS providers administer an antiarrhythmic infusion in an effort to prevent the patient from re-arresting. The 2010 Guidelines acknowledged that although patients could receive antiarrhythmics during this time, there was no evidence to support or refute the continued use of any prophylactic antiarrhythmic agent during the post-resuscitation period .
For the 2015 Guidelines, the AHA reexamined this issue. One prehospital observational study of OOH cardiac arrest patients found conflicting results . Using one method of data analysis found an association between prophylactic lidocaine administration during the post cardiac arrest period and reduced odds of re-arrest from either VF/pVT or non-shockable rhythms, improved survival to hospital admission rates, and improved survival to hospital discharge rates. A second method of data analysis could only demonstrate a reduction in re-arrest from VF/pVT following lidocaine administration. Therefore, the AHA changed the previous recommendation to state that health care providers can consider administering lidocaine once the patient achieves ROSC following VF/pVT.
Beta blocker use after ROSC?
The AHA also looked at another class of antiarrhythmic medications not commonly used for cardiac arrest in the OOH environment. An observational study of in-hospital cardiac arrest found that either oral or intravenous administration of beta-blocking agents within the first 72 hours of the post resuscitation period was associated with survival to hospital discharge . The AHA now recommends that hospital personnel consider administering either oral or intravenous beta-blockers within 72 hours of admission following cardiac arrest due to VF/pVT. This recommendation does not extend to the OOH environment.
Targeted Temperature Management – how cold?
The AHA made several modifications to the existing recommendations concerning targeted temperature management (TTM). In 2010, the strength of recommendation for initiating therapeutic hypothermia varied depending on cardiac arrest rhythm and location of the arrest . The current guidelines upgrade the strength of the recommendation for TTM to the highest level for all comatose patients who achieve ROSC regardless of the presenting rhythm or whether the arrest occurred in the OOH or hospital environment.
The previous guidelines recommended that health care providers achieve a temperature of 32 C to 34 C. Since publication of those guidelines, one RCT compared the outcomes between patients cooled to 33 C and those cooled to 36 C . There was no difference in mortality or neurologic function between the two groups suggesting that cooler temperatures conferred no outcome advantages. As a result, the AHA expanded the target range for hypothermia to temperature of 32 C to 36 C.
The AHA no longer recommends the prehospital use of chilled saline as a method of inducing hypothermia. Five RCTs using chilled IV fluids following ROSC [118-122], one trial using chilled IV fluids during the resuscitation attempt , and one trial using intra-nasal cooling  could find no survival or neurological recovery benefits offered by prehospital cooling. In one of the chilled saline trials, initiating cooling in the field actually increased the risk of re-arrest and post resuscitation pulmonary edema .
Destination criteria for post cardiac arrest?
The AHA attempted to answer the question of whether transport to a facility that specializes in the care of a patient who has suffered an OOH cardiac arrest improves the outcome. Although the data is limited, there is one prospective study that indirectly addressed the question . Researchers found that transport to a critical care facility improved neurologically favorable one-month mortality compared to transport to a non-critical care facility, even when the patient did not achieve ROSC in the field. Thus the AHA recommends that EMS agencies collaborate with key stakeholders in the community and approach the problem of OOH cardiac arrest from a system perspective rather than from an individual agency standpoint. Part of this approach is the consideration of transport to specialized cardiac arrest hospitals.
Termination of resuscitation by EMS providers
The AHA recommends EMS personnel consider terminating the resuscitation efforts when the team is unable to achieve an ETCO2 reading greater than 10 mm Hg 20 minutes after intubation. However the AHA does not recommend using ETCO2 readings as the sole criterion for making that decision. Additionally, the AHA advises against using any ETCO2 value as a criterion for making a decision to terminate resuscitation in non-intubated patients.
Expect continuous updates to the guidelines
Overall, changes in the 2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care are relatively minor. The publication represents the culmination of years of work by the most respected resuscitation researchers in the world. This publication also marks the beginning of a new era in resuscitation guidelines as the American Heart Association transitions away from a five-year periodic update to a web-based format that will allow continuous updates. This should help minimize the inconsistencies that sometimes occur when EMS Medical Directors update system protocols and treatment guidelines with new science between the five-year official updates made by the American Heart Association.
About the Author
Kenny Navarro is an Assistant Professor in the Emergency Medicine Education Department at the University of Texas Southwestern Medical Center at Dallas. He coordinates all continuing education activities and assists in medical oversight for BioTel, a multi-jurisdictional EMS system composed of 14 fire/rescue agencies and more than 1,500 paramedics. Mr. Navarro serves as a Content Consultant for the AHA ACLS Project Team for Guidelines 2010 and served on two education subcommittees for NIH-funded research projects, as the Coordinator for the National EMS Education Standards Project, and as an expert writer for the National EMS Education Standards Implementation Team. Send correspondence concerning any articles in this section to Kenneth W. Navarro, The University of Texas Southwestern Medical School at Dallas, 6300 Harry Hines Blvd, MC 9134, Dallas, Texas 75390-9134