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CPR being administered during a simulation of cardiac arrest.
|Classification and external resources|
CPR being administered during a simulation of cardiac arrest.
Cardiac arrest, also known as cardiopulmonary arrest or circulatory arrest, is a sudden stop in effective blood circulation due to failure of the heart to contract effectively or at all. Medical personnel may refer to an unexpected cardiac arrest as a sudden cardiac arrest (SCA).
A cardiac arrest is different from (but may be caused by) a heart attack, where blood flow to the muscle of the heart is impaired. It is different from congestive heart failure, where circulation is substandard, but the heart is still pumping sufficient blood to sustain life.
Arrested blood circulation prevents delivery of oxygen and glucose to the body. Lack of oxygen and glucose to the brain causes loss of consciousness, which then results in abnormal or absent breathing. Brain injury is likely to happen if cardiac arrest goes untreated for more than five minutes. For the best chance of survival and neurological recovery, immediate and decisive treatment is imperative.
Cardiac arrest is a medical emergency that, in certain situations, is potentially reversible if treated early. Unexpected cardiac arrest can lead to death within minutes: this is called sudden cardiac death (SCD). The treatment for cardiac arrest is immediate defibrillation if a "shockable" rhythm is present, while cardiopulmonary resuscitation (CPR) is used to provide circulatory support and/or to induce a "shockable" rhythm.
Clinicians classify cardiac arrest into "shockable" versus "non–shockable", as determined by the ECG rhythm. This refers to whether a particular class of cardiac dysrhythmia is treatable using defibrillation. The two "shockable" rhythms are ventricular fibrillation and pulseless ventricular tachycardia while the two "non–shockable" rhythms are asystole and pulseless electrical activity.
Cardiac arrest is an abrupt cessation of pump function in the heart (as evidenced by the absence of a palpable pulse). Prompt intervention can usually reverse a cardiac arrest, but without such intervention it will almost always lead to death. In certain cases, it is an expected outcome to a serious illness.
However, due to inadequate cerebral perfusion, the patient will be unconscious and will have stopped breathing. The main diagnostic criterion to diagnose a cardiac arrest (as opposed to respiratory arrest which shares many of the same features) is lack of circulation; however, there are a number of ways of determining this. Near death experiences are reported by 10-20% of people who survived cardiac arrest.
Coronary heart disease is the leading cause of sudden cardiac arrest. Many other cardiac and non-cardiac conditions also increase one's risk.
Approximately 60–70% of SCD is related to coronary heart disease. Among adults, ischemic heart disease is the predominant cause of arrest with 30% of people at autopsy showing signs of recent myocardial infarction.
In a group of military recruits aged 18–35, cardiac anomalies accounted for 51% of cases of SCD, while in 35% of cases the cause remained unknown. Underlying pathology included: coronary artery abnormalities (61%), myocarditis (20%), and hypertrophic cardiomyopathy (13%). Congestive heart failure increases the risk of SCD by 5 fold.
Many additional conduction abnormalities exist that place one at higher risk for cardiac arrest. For instance, long QT syndrome, a condition often mentioned in young people's deaths, occurs in 1/5000-1/7000 newborns and is estimated to be responsible 3000 deaths each year compared to the approximately 300000 cardiac arrests seen by emergency services . These conditions are a fraction of the overall deaths related to cardiac arrest, but represent conditions which may be detected prior to arrest, which may be treatable.
SCDs is unrelated to heart problems in 35% of cases. The most common non-cardiac causes: trauma, non-trauma related bleeding (such as gastrointestinal bleeding, aortic rupture, and intracranial hemorrhage), overdose, drowning and pulmonary embolism. Environmental toxins from for example certain jellyfish may also cause cardiac arrest.
Cardiac arrest is synonymous with clinical death.
A cardiac arrest is usually diagnosed clinically by the absence of a pulse. In many cases lack of carotid pulse is the gold standard for diagnosing cardiac arrest, but lack of a pulse (particularly in the peripheral pulses) may result from other conditions (e.g. shock), or simply an error on the part of the rescuer. Studies have shown that rescuers often make a mistake when checking the carotid pulse in an emergency, whether they are healthcare professionals or lay persons.
Owing to the inaccuracy in this method of diagnosis, some bodies such as the European Resuscitation Council (ERC) have de-emphasised its importance. The Resuscitation Council (UK), in line with the ERC's recommendations and those of the American Heart Association, have suggested that the technique should be used only by healthcare professionals with specific training and expertise, and even then that it should be viewed in conjunction with other indicators such as agonal respiration.
Various other methods for detecting circulation have been proposed. Guidelines following the 2000 International Liaison Committee on Resuscitation (ILCOR) recommendations were for rescuers to look for "signs of circulation", but not specifically the pulse. These signs included coughing, gasping, colour, twitching and movement. However, in face of evidence that these guidelines were ineffective, the current recommendation of ILCOR is that cardiac arrest should be diagnosed in all casualties who are unconscious and not breathing normally.
With positive outcomes following cardiac arrest unlikely, an effort has been spent in finding effective strategies to prevent cardiac arrest. With the prime causes of cardiac arrest being ischemic heart disease, efforts to promote a healthy diet, exercise, and smoking cessation are important. For people at risk of heart disease, measures such as blood pressure control, cholesterol lowering, and other medico-therapeutic interventions are used.
In medical parlance, cardiac arrest is referred to as a "code" or a "crash". This typically refers to "code blue" on the hospital emergency codes. A dramatic drop in vital sign measurements is referred to as "coding" or "crashing", though coding is usually used when it results in cardiac arrest, while crashing might not. Treatment for cardiac arrest is sometimes referred to as "calling a code".
Extensive research has shown that patients in general wards often deteriorate for several hours or even days before a cardiac arrest occurs. This has been attributed to a lack of knowledge and skill amongst ward based staff, in particular a failure to carry out measurement of the respiratory rate, which is often the major predictor of a deterioration and can often change up to 48 hours prior to a cardiac arrest. In response to this, many hospitals now have increased training for ward based staff. A number of "early warning" systems also exist which aim to quantify the risk which patients are at of deterioration based on their vital signs and thus provide a guide to staff. In addition, specialist staff are being utilised more effectively in order to augment the work already being done at ward level. These include:
In some medical facilities, the resuscitation team may purposely respond slowly to a patient in cardiac arrest, a practice known as slow code, or may fake the response altogether for the sake of the patient's family, a practice known as show code. This is generally done for patients for whom performing CPR will have no medical benefit. Such practices are ethically controversial, and are banned in some jurisdictions.
A technologically based intervention to prevent further cardiac arrest episodes is the use of an implantable cardioverter-defibrillator (ICD). This device is implanted in the patient and acts as an instant defibrillator in the event of arrhythmia. Note that standalone ICDs do not have any pacemaker functions, but they can be combined with a pacemaker, and modern versions also have advanced features such as anti-tachycardic pacing as well as synchronized cardioversion. A recent study by Birnie et al. at the University of Ottawa Heart Institute has demonstrated that ICDs are underused in both the United States and Canada. An accompanying editorial by Simpson explores some of the economic, geographic, social and political reasons for this. Patients who are most likely to benefit from the placement of an ICD are those with severe ischemic cardiomyopathy (with systolic ejection fractions less than 30%) as demonstrated by the MADIT-II trial.
Sudden cardiac arrest may be treated via attempts at resuscitation. This is usually carried out based upon basic life support (BLS) / advanced cardiac life support (ACLS), pediatric advanced life support (PALS) or neonatal resuscitation program (NRP) guidelines.
CPR is a important part of the management of cardiac arrest. It is recommended that it be started as soon as possible and interrupted as little as possible. The component of CPR which seems to make the greatest difference in most cases is the chest compressions. Correctly performed bystander CPR has been shown to increase survival; however, it is performed in less than 30% of out of hospital arrests as of 2007. If high quality CPR has not resulted in return of spontaneous circulation and the person's heart rhythm is in asystole discontinuing CPR and pronouncing the person death is reasonable after 20 minutes. Exceptions to this include those with hypothermia or who have drowned. Longer durations of CPR may be reasonable in those who have cardiac arrest while in hospital.
Tracheal intubation has not been found to improve survival rates in cardiac arrest and in the prehospital environment may worsen it. A 2009 study found that assisted ventilation may worsen outcomes over placement of an oral airway with passive oxygen delivery.
CPR which involves only chest compressions results in the same outcomes as standard CPR for those who have gone into cardiac arrest due to heart issues. A 2013 review found some evidence that mechanical chest compressions (as performed by a machine) are better than manual chest compressions while a 2011 and 2012 review considered the evidence insufficient.
Shockable and non–shockable causes of cardiac arrest is based on the presence or absence of ventricular fibrillation or pulseless ventricular tachycardia. The shockable rhythms are treated with CPR and defibrillation.
In addition, there is increasing use of public access defibrillation. This involves placing automated external defibrillators in public places, and training staff in these areas how to use them. This allows defibrillation to take place prior to the arrival of emergency services, and has been shown to lead to increased chances of survival. Some defibrillators even provide feedback on the quality of CPR compressions, encouraging the lay rescuer to press the patient's chest hard enough to circulate blood. In addition, it has been shown that those who have arrests in remote locations have worse outcomes following cardiac arrest.
Medications, while included in guidelines, have been shown not to improve survival to hospital discharge post out of hospital cardiac arrest. This includes the use of epinephrine, atropine, and amiodarone. Vasopressin overall does not improve or worsen outcomes but may be of benefit in those with asystole especially if used early.
The 2010 guidelines, from the American Heart Association has removed its recommendation for using atropine in pulseless electrical activity and asystole due to the lack of evidence for its use. Evidence is insufficient for lidocaine and amiodarone may be considered in those who continue in ventricular tachycardia or ventricular fibrillation despite defibrillation. Thrombolytics when used generally may cause harm but may be of benefit in those with a pulmonary embolism as the cause of arrest.
Cooling a person after cardiac arrest with return of spontaneous circulation (ROSC) but without return of consciousness may or may not improve outcomes. This procedure is called therapeutic hypothermia. People are cooled over a 24 hour period, with a target temperature of 32–34 °C (90–93 °F). Death rates in the hypothermia group were initially believed to be 35% lower with generally mild complications. A November 2013 trial, however, called this idea into question with findings that a temperature of 36 °C (97 °F) results in the same outcomes as 33 °C (91 °F). And a second trial looking at earlier versus later cooling found no difference.
Some people choose to avoid aggressive measures at the end of life. A do not resuscitate order (DNR) in the form of an advance health care directive makes it clear that in the event of cardiac arrest, the person does not wish to receive cardiopulmonary resuscitation. Other directives may be made to stipulate the desire for intubation in the event of respiratory failure or, if comfort measures are all that are desired, by stipulating that healthcare providers should "allow natural death".
Several organisations promote the idea of a chain of survival. The chain consists of the following "links":
If one or more links in the chain are missing or delayed, then the chances of survival drop significantly.
These protocols are often initiated by a code blue, which usually denotes impending or acute onset of cardiac arrest or respiratory failure, although in practice, Code Blue is often called in less life-threatening situations that require immediate attention from a physician.
The precordial thump may be considered in those with witnessed, monitored, unstable ventricular tachycardia (including pulseless VT) if a defibrillator is not immediately ready for use, but it should not delay CPR and shock delivery or be used in those with unwitnessed out of hospital arrest. Resuscitation with extracorporeal membrane oxygenation devices has been attempted with better results for in-hospital cardiac arrest (29% survival) than out of hospital cardiac arrest (4% survival) in populations selected to benefit most.
The survival rate of people who receive initial emergency care by ambulance is only 2%, with 15% experiencing return of spontaneous circulation. However, with defibrillation within 3–5 minutes, the survival rate increases to 30%.
Since mortality in case of out-of-hospital cardiac arrest is high, programs were developed to improve survival rate. Although mortality in case of ventricular fibrillation is high, rapid intervention with a defibrillator increases survival rate.
Survival is mostly related to the cause of the arrest (see above). In particular, patients who have suffered hypothermia have an increased survival rate, possibly because the cold protects the vital organs from the effects of tissue hypoxia. Survival rates following an arrest induced by toxins is very much dependent on identifying the toxin and administering an appropriate antidote. A patient who has suffered a myocardial infarction due to a blood clot in the left coronary artery has a lower chance of survival.
A study of survival rates from out of hospital cardiac arrest found that 14.6% of those who had received resuscitation by ambulance staff survived as far as admission to hospital. Of these, 59% died during admission, half of these within the first 24 hours, while 46% survived until discharge from hospital. This gives us an overall survival following cardiac arrest of 6.8%. Of these 89% had normal brain function or mild neurological disability, 8.5% had moderate impairment, and 2% suffered major neurological disability. Of those who were discharged from hospital, 70% were still alive 4 years later.
A review into outcomes following in-hospital cardiac arrest found a survival to discharge of 14% although the range between different studies was 0-28%.
Based on death certificates sudden cardiac death accounts for about 15% of all death in Western countries (330,000 per year in the United States). The lifetime risk is three times greater in men (12.3%) than women (4.2%) based on analysis of the Framingham Heart Study. However this gender difference disappeared beyond 85 years of age.
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