designated staff members with particular expertise in resuscitation who are called to the scene of all arrests within the hospital. this usually involves a specialized cart of equipment (including a defibrillator) and drugs called a "crash cart" or "crash trolley". medical emergency teams – these teams respond to all emergencies with the aim of treating people in the acute phase of their illness in order to prevent a cardiac arrest. these teams have been found to decrease the rates of in-hospital cardiac arrest (ihca) and improve survival. critical care outreach – in addition to providing the services of the other two types of teams, these teams are responsible for educating non-specialist staff. in addition, they help to facilitate transfers between intensive care/high dependency units and the general hospital wards. this is particularly important as many studies have shown that a significant percentage of patients discharged from critical care environments quickly deteriorate and are re-admitted; the outreach team offers support to ward staff to prevent this from happening. implantable cardioverter defibrillator illustration of implantable cardioverter defibrillator (icd) an implantable cardioverter defibrillator (icd) is a battery-powered device that monitors electrical activity in the heart, and when an arrhythmia is detected, can deliver an electrical shock to terminate the abnormal rhythm. icds are used to prevent sudden cardiac death (scd) in those who have survived a prior episode of sudden cardiac arrest (sca) due to ventricular fibrillation or ventricular tachycardia (secondary prevention). icds are also used prophylactically to prevent sudden cardiac death in certain high-risk patient populations (primary prevention). numerous studies have been conducted on the use of icds for the secondary prevention of scd. these studies have shown improved survival with icds compared to the use of anti-arrhythmic drugs. icd therapy is associated with a 50% relative risk reduction in death caused by an arrhythmia and a 25% relative risk reduction in all-cause mortality. primary prevention of scd with icd therapy for high-risk patient populations has similarly shown improved survival rates in several large studies. the high-risk patient populations in these studies were defined as those with severe ischemic cardiomyopathy (determined by a reduced left ventricular ejection fraction (lvef)). the lvef criteria used in these trials ranged from less than or equal to 30% in madit-ii to less than or equal to 40% in mustt. management sudden cardiac arrest may be treated via attempts at resuscitation. this is usually carried out based on basic life support, advanced cardiac life support (acls), pediatric advanced life support (pals), or neonatal resuscitation program (nrp) guidelines. cpr training on a mannequin cardiopulmonary resuscitation early cardiopulmonary resuscitation (cpr) is essential to surviving cardiac arrest with good neurological function. it is recommended that it be started as soon as possible with minimal interruptions once begun. the components of cpr that make the greatest difference in survival are chest compressions and defibrillating shockable rhythms. after defibrillation, chest compressions should be continued for two minutes before another rhythm check. this is based on a compression rate of 100-120 compressions per minute, a compression depth of 5–6 centimeters into the chest, full chest recoil, and a ventilation rate of 10 breath ventilations per minute. correctly performed bystander cpr has been shown to increase survival; it is performed in fewer than 30% of out-of-hospital cardiac arrests (ohcas) as of 2007. if high-quality cpr has not resulted in return of spontaneous circulation (rosc) and the person's heart rhythm is in asystole, discontinuing cpr and pronouncing the person's death is generally reasonable after 20 minutes. exceptions to this include certain cases with hypothermia or drowning victims. some of these cases should have longer and more sustained cpr until they are nearly normothermic. longer durations of cpr may be reasonable in those who have cardiac arrest while in hospital. bystander cpr by the lay public before the arrival of ems also improves outcomes. either a bag valve mask or an advanced airway may be used to help with breathing particularly since vomiting and regurgitation are common, especially in ohca. if this occurs, then modification to existing oropharyngeal suction may be required, such as the use of suction assisted laryngoscopy airway decontamination. high levels of oxygen are generally given during cpr. tracheal intubation has not been found to improve survival rates or neurological outcomes in cardiac arrest and in the prehospital environment, may worsen it. endotracheal tubes and supraglottic airways appear equally useful. when done by ems, 30 compressions followed by two breaths appear better than continuous chest compressions and breaths being given while compressions are ongoing. for bystanders, cpr that involves only chest compressions results in better outcomes as compared to standard cpr for those who have gone into cardiac arrest due to heart issues. mouth-to-mouth as a means of providing respirations to the patient has been phased out due to the risk of contracting infectious diseases from the patient. mechanical chest compressions (as performed by a machine) are no better than chest compressions performed by hand. it is unclear if a few minutes of cpr before defibrillation results in different outcomes than immediate defibrillation. if cardiac arrest occurs after 20 weeks of pregnancy, the uterus should be pulled or pushed to the left during cpr. if a pulse has not returned by four minutes, an emergency cesarean section is recommended. defibrillation an automated external defibrillator stored in a visible orange mural support defibrillation is indicated if an electric-shockable heart rhythm is present. the two shockable rhythms are ventricular fibrillation and pulseless ventricular tachycardia. in children, 2 to 4 j/kg is recommended. in out-of-hospital arrests, the defibrillation is made by an automated external defibrillator (aed), a portable machine that can be used by any user: it provides voice instructions that guide the process, automatically checks the victim's condition, and applies the appropriate electric shocks. some defibrillators even provide feedback on the quality of cpr compressions, encouraging the lay rescuer to press the person's chest hard enough to circulate blood. in addition, there is increasing use of public access defibrillation. this involves placing aeds in public places and training staff in these areas on how to use them. this allows defibrillation to occur prior to the arrival of emergency services, which has been shown to increase chances of survival. it has been shown that those who have arrests in remote locations have worse outcomes following cardiac arrest. medications lipid emulsion as used in cardiac arrest due to local anesthetic agents as of 2016, medications other than epinephrine (adrenaline), while included in guidelines, have not been shown to improve survival to hospital discharge following ohcas. this includes the use of atropine, lidocaine, and amiodarone. epinephrine in adults, as of 2019, appears to improve survival but does not appear to improve neurologically normal survival. it is generally recommended every three to five minutes. epinephrine acts on the alpha-1 receptor, which in turn increases the blood flow that supplies the heart. this would assist with providing more oxygen to the heart. based on 2019 guidelines, 1 mg of epinephrine may be administered to patients every 3–5 minutes, but doses higher than 1 mg of epinephrine are not recommended for routine use in cardiac arrest. if the patient has a non-shockable rhythm, epinephrine should be administered as soon as possible. for a shockable rhythm, epinephrine should only be administered after an initial defibrillation attempt. vasopressin overall does not improve or worsen outcomes compared to epinephrine. the combination of epinephrine, vasopressin, and methylprednisolone appears to improve outcomes. some of the lack of long-term benefits may be related to delays in epinephrine use. while evidence does not support its use in children, guidelines state its use is reasonable. lidocaine and amiodarone are also deemed reasonable in children with cardiac arrest who have a shockable rhythm. the general use of sodium bicarbonate or calcium is not recommended. the use of calcium in children has been associated with poor neurological function as well as decreased survival. correct dosing of medications in children is dependent on weight. to minimize time spent calculating medication doses, the use of a broselow tape is recommended. the 2010 guidelines from the american heart association no longer contain the recommendation for using atropine in pulseless electrical activity and asystole for lack of evidence supporting its use. neither lidocaine nor amiodarone, in those who continue in ventricular tachycardia or ventricular fibrillation despite defibrillation, improves survival to hospital discharge, despite both equally improving survival to hospital admission. thrombolytics may cause harm but may be of benefit in those with a confirmed pulmonary embolism as the cause of arrest. evidence for use of naloxone in those with cardiac arrest due to opioids is unclear, but it may still be used. in those with cardiac arrest due to local anesthetic, lipid emulsion may be used. targeted temperature management current international guidelines suggest cooling adults after cardiac arrest using targeted temperature management (ttm), which was previously known as therapeutic hypothermia. people are typically cooled for a 24-hour period, with a target temperature of 32–36 °c (90–97 °f). there are several methods used to lower the body temperature, such as applying ice packs or cold-water circulating pads directly to the body or infusing cold saline. this is followed by gradual rewarming over the next 12 to 24 hrs. the effectiveness of ttm after ohca is an area of ongoing study. pre-hospital ttm after ohca has been shown to increase the risk of adverse outcomes. the rates of re-arrest may be higher in people who were treated with pre-hospital ttm. ttm in post-arrest care has not been found to improve mortality or neurological outcomes. moreover, ttm may have adverse neurological effects in people who survive post-cardiac arrest. do not resuscitate 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". chain of survival several organizations promote the idea of a chain of survival. the chain consists of the following "links": early recognition. if possible, recognition of illness before the person develops a cardiac arrest will allow the rescuer to prevent its occurrence. early recognition that a cardiac arrest has occurred is key to survival, for every minute a patient stays in cardiac arrest, their chances of survival drop by roughly 10%. early cpr improves the flow of blood and of oxygen to vital organs, an essential component of treating a cardiac arrest. in particular, by keeping the brain supplied with oxygenated blood, the chances of neurological damage are decreased. early defibrillation is effective for the management of ventricular fibrillation and pulseless ventricular tachycardia. early advanced care. early post-resuscitation care, which may include percutaneous coronary intervention. 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. other resuscitation with extracorporeal membrane oxygenation devices has been attempted with better results for in-hospital cardiac arrest (29% survival) than ohca (4% survival) in populations selected to benefit most. cardiac catheterization in those who have survived an ohca appears to improve outcomes, although high-quality evidence is lacking. it is recommended to be done as soon as possible in those who have had a cardiac arrest with st elevation due to underlying heart problems. 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 ohca. prognosis the overall rate of survival among those who have cardiac arrest outside the hospital is 10%. among those who have an ohca, 70% occur at home, and their survival rate is 6%. for those who have an in-hospital cardiac arrest (ihca), the survival rate one year from at least the occurrence of cardiac arrest is estimated to be 13%. one-year survival is estimated to be higher in people with cardiac admission