This is the sub-section of the Digital Research Library containing all material on the topic of out-of-hospital sudden cardiac arrest (OHCA), resuscitation, the cardiac chain of survival, CPR, chest compressions, ventilation and rescue breathing, defibrillation, and intra-arrest drugs.
Overview
Cardiac arrest care has been at the heart of prehospital medicine since its inception, and much of modern EMS is dedicated to providing optimal care for cases of out-of-hospital SCA (sudden cardiac arrest). Since the first introduction of CPR and defibrillation in the 1960s, a large body of research has investigated best practices for maximizing survival in this high-mortality cohort.
Every five years, the International Liaison Committee on Resuscitation (ILCOR) reviews the existing evidence and issues revised guidelines for resuscitation, which are adopted internationally (with small customizations) as standard of care for SCA. In the US, this is via the American Heart Association (AHA), whose recommendations are published in the Circulation journal; the most recent was released in 2010. These are heavily cited and well-supported documents, and their reference list can be easily mined for the relevant studies on various subjects.
When reviewing the literature, it is important to consider both the baseline details of the cohort studied, and the endpoints being evaluated. Vastly different outcomes may be seen between populations depending on their proportion of witnessed arrests, frequency of bystander CPR, time-to-EMS-arrival, and other baseline variables; research from Singapore may, therefore, lack external validity in Seattle. Conversely, when considering outcomes, there is a cascading series of nested, yet distinct endpoints: how many patients achieved a return of spontaneous circulation (ROSC)? How many of those survived to hospital admission? How many of those survived to hospital discharge? And how many of those were discharged neurologically intact? Only survival to neurologically-intact discharge is generally accepted as “true” survival (dying in the ICU is not better than dying on scene); however, many interventions may improve short-term outcome (such as ROSC) without improving this ultimate endpoint, and the value of such measures is debatable.
Much of the existing research focuses in several areas:
Pharmacology: Drugs have been given to SCA patients during resuscitation for many years. Some have been shown ineffective or harmful and are no longer routinely recommend (bretylium, isoproterenol, bicarbonate, atropine, etc). Others are still believed to be potentially valuable (epinephrine, amiodarone). In general, the support for drugs is based on physiological reasoning and their success in improving surrogate endpoints — such as coronary perfusion or rate of ROSC (return of spontaneous circulation) in laboratory trials (eg. swine models). Although some drugs have been shown to increase the chance of ROSC, no drug has ever consistently demonstrated an improved chance of survival to hospital discharge with good neurological status, and some drugs may improve ROSC but actually decrease survival to discharge. Randomized controlled trials are rare, (although see Olasveengen [2009] and Jacobs for epinephrine, and Kudenchuk for amiodarone). AHA guidelines now deemphasize pharmacological interventions such as epinephrine due to this absence of evidence for true survival, but do not (yet) recommend against their use altogether. Promising novel drugs such as intra-arrest nitrates and female sex hormones are currently being studied.
Chest compressions: External chest compressions remain a core component of resuscitation. A growing body of evidence has demonstrated the positive effect of chest compressions on survival, more recently emphasizing the importance of their quality, namely compressions that: are initiated as early as possible after collapse; are continued without any interruption; are deep, fast, and recoil fully; and are not compromised for other interventions except defibrillation. A variation known as cardiocerebral resuscitation (CCR), or “hands only CPR” has been shown to improve survival over CPR-with-ventilation; this is now recommended for lay providers (due to ease of training, effectiveness, and bystander reluctance to administer mouth-to-mouth breaths), and many EMS services are increasingly adopting resuscitation protocols that embrace these principles.
Ventilation: Insufflation of oxygen-rich air into the patient’s lungs is a traditional component of CPR. In recent years the importance of this has been deemphasized, due to the low oxygen demands of a poorly-perfusing patient, high levels of reserve oxygen after sudden collapse, passive air movement provided by chest compressions, and the deleterious effect on circulation of frequent pauses for positive-pressure ventilation. Most high-performance EMS systems have adopted the practice of providing ventilations only after compressions and defibrillation have been addressed, except when arrest is presumed secondary to hypoxic causes. Otherwise, ventilation (by BVM or particularly intubation) has generally been shown to have no effect, or to have a deleterious effect, upon survival.
Defibrillation: Electrical cardioversion remains the definitive treatment for ventricular fibrillation or pulseless ventricular tachycardia. Research has generally shown the effect of different pad/paddle positions, electrical waveforms or amperages, and other details to be minimal; however, early defibrillation is unquestionably key to survival. Automated external defibrillators (AEDs) have been shown to be safe and generally as effective as manual monitor/defibrillators, and are usable by willing lay providers when available in public areas. Specialized techniques such as “double sequential external defibrillation” (DSED) for refractory v-fib are currently being studied.
Adjunctive devices: Numerous devices have been developed to potentially improve the effectiveness of CPR. Mechanical compression devices that administer automated chest compressions (using battery or compressed-gas power) are now offered by several manufacturers, and have generally been shown to be equally effective to high-quality manual compressions, although not superior. An “impedence threshold device” or ITD is offered by one manufacturer (as the ResQPod), which creates negative pressure inside the thorax to improve cardiac preload; early research was ambiguous as to its effectiveness, but more recent studies have suggested it may have benefit when combined with active compression-decompression CPR (ACD-CPR, which uses plunger-like devices to allow for both compression and active “pulling” during recoil). Monitors or AEDs that provide real-time audiovisual feedback during CPR, ensuring that rescuers provide compressions at the desired rate and depth, are increasingly common and may improve CPR quality.
Post-arrest care and therapeutic hypothermia: Post-arrest hypothermia, where a patient is cooled after ROSC is obtained (generally only if they remain comatose), has been definitively shown to improve survival to discharge with good neurological status. Most of this research is for shockable rhythms; evidence for its use after asystole or PEA is minimal, although most clinicians presume its effectiveness. Details such as target temperature, time-at-temperature, when to induce (prehospital cooling has become increasingly common, in some cases initiated intra-arrest, but has not been shown to improve outcomes over later induction in the ED), and other matters have not yet been established in large trials. Manner of cooling has generally been shown to be immaterial; chilled saline, external ice packs, and external cooling blankets are currently the most common approaches, although invasive techniques (such as peritoneal lavage) are also available. Other post- or peri-arrest therapies, such as early PCI for patients with STEMI (perhaps even prior to ROSC), emergency ECMO, “ischemic preconditioning,” and more are currently being studied.
Prevalence, prognosis, and community health: Due to the importance of bystander intervention in recognizing SCA, activating EMS, and providing early CPR and defibrillation, as well as the importance of rapid EMS response, ample research has been done into: risk factors for arrest; prognosis for arrest at various times and settings; impact on survival of common EMS models and response times; impact of bystander compressions, AED use, dispatch-delivered telephone instructions for CPR, and other measures; and optimal strategies for improving bystander willingness and ability to intervene for SCA patients.
Editor’s note: this shelf is still in the early stages of development. A substantial amount of important material still remains to be added before the state of the literature is effectively represented.
Updates
To view newly added material, search for the triple asterisk (***)
[1-14-14] 3 papers added.
[5-13-13] 6 papers added.
[4-18-13] Shelf created. 9 papers added.
Index
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