Cardiopulmonary resuscitation (CPR) is a collection of interventions performed to provide oxygenation and circulation to the body during cardiac arrest. Our current modern-day approach to this process stemmed from the work of a handful of doctors in the 1950s and has now evolved into the process that will be discussed further here. The most widely accepted guidelines in North America are those produced by the American Heart Association (AHA). These are published every 5 years, after the International Liaison Committee on Resuscitation (ILCOR) meeting. 
Every year almost 350,000 Americans die from heart disease. Half of these will die suddenly, outside of a hospital, because of the sudden cessation of spontaneous organized cardiac function. The most common cause of sudden cardiac arrest in adults is ventricular fibrillation. Although advances in emergency cardiac care continue to improve the chances of survival, sudden cardiac arrest remains a leading cause of death in many parts of the world. As of 2016, cardiac disease continues to be the leading cause of death in the United States.
Seventy percent of cardiac arrests that occur outside of a hospital occur in the home. Half of these cardiac arrests are unwitnessed. Despite advances in emergency medical services, the survival rate remains low. Adult victims of non-traumatic cardiac arrest that receive resuscitation attempts by emergency medical services have a survival rate to hospital discharge of only 10.8%. In comparison, adult patients who experience cardiac arrest in a hospital setting have rates of survival to hospital discharge of up to 25.5%. 
The definitive treatment for ventricular fibrillation is electrical defibrillation. This is most often performed using an automated external defibrillator (AED). If an AED is not readily available for defibrillation, brain death is likely to occur in less than 10 minutes. CPR is a means of providing artificial circulation and ventilation until defibrillation can be performed. Conventional manual CPR, combining chest compressions with rescue breathing can provide up to 33% of normal cardiac output and oxygenation when done properly. 
Patients requiring CPR are unconscious and unresponsive with absent pulses. There is a prognostic benefit in determining the last time the patient was seen normal, or better yet, the time when pulses were lost. Additionally, collateral history from bystanders, family members, friends, and the primary care physician can help etiologic evaluation.
There are no specific physical examination findings, but signs of cyanosis and reduced peripheral perfusion can suggest a cause for the arrest.
The absence of a palpable pulse in an unresponsive patient indicates the need for CPR.
Note: The technique described here is intended for a healthcare provider performing one-rescuer CPR on an adult victim in the out-of-hospital setting. The modifications for children, infants, and for in-hospital CPR are listed below. These recommendations are current as of the 2015 American Heart Association's Guidelines update for CPR and Emergency Cardiac Care.
The immediate recognition of cardiac arrest is essential to both initiate the emergency medical services (EMS) response and to begin CPR as soon as possible. In this era of universal mobile phone availability, it is now possible to call 911 while remaining with the victim. Make sure that the scene is safe, then call for help. Simultaneously, begin CPR by first performing chest compressions (C), followed by opening the airway (A) and delivering rescue breaths (B) (the CAB sequence as compared to the former ABC sequence). The hands are placed on the lower half of the sternum, and chest compressions are begun at a rate of 100 to 120 compressions per minute. The goal is to depress the sternum to a depth of at least two inches while avoiding excessive depth of compressions. The chest wall should be allowed to recoil fully on the upstroke to maintain coronary artery perfusion pressure.  Thirty compressions are performed, followed by a brief pause for two rescue breaths. Because of the critical contribution of chest compressions to coronary artery perfusion, interruptions in chest compressions should be minimized, and any interruptions should be as short as possible when needed. 
After 30 chest compressions, the rescuer performs a head tilt/chin lift maneuver to open the airway (assuming there is no suspicion of a cervical spinal injury). If a cervical spine injury is suspected, the airway is opened by using the jaw-thrust maneuver without extending the head. Two rescue breaths are administered: the rescuer takes a "regular" breath (not deep or excessive) and delivers a rescue breath lasting approximately one second, which should be enough just to allow the chest to rise. The process is repeated for a second rescue breath prior to resuming chest compressions.
Ideally, a healthcare provider who is inclined to intervene as an out-of-hospital rescuer should have ready access to a barrier device such as a rescue mask. However, this is not always the case. Mouth-to-mouth rescue breaths have been the alternative, which many untrained rescuers are hesitant to perform, especially on an unknown victim. This is a decision that healthcare providers must make for themselves. Compression-only CPR has been accepted as appropriate for untrained lay rescuers. If extenuating circumstances prohibit a healthcare provider in the out-of-hospital setting from performing rescue breathing without a barrier device, compression-only CPR should be performed until EMS arrives. 
The cycle of 30 chest compressions alternated with two rescue breaths is continued until an AED becomes available, or until additional help arrives. If an AED arrives, its pads should be applied to the front and back of the patient, taking care to minimize any delay in restarting chest compressions. Most modern devices verbalize further instructions—after attached to the patient, AEDs will detect the current cardiac rhythm and advise whether the patient should receive defibrillation. If the AED advises shock, cease chest compressions and stay clear of the patient until defibrillation is completed. After defibrillation is completed, or if no shock is advised, immediately resume cycles of chest compressions and rescue breaths following the CAB sequence until additional help arrives.
A quick physical exam focused on palpable pulses and mental status is important as sometimes drug overdose including heavy alcohol intake may mimic cardiac arrest.
According to 2015 AHA data, survival to hospital discharge in patients who experience out-of-hospital cardiac arrest remains low at 10.6%. 8.3% of patients experiencing cardiac arrest out-of-hospital will be discharged with good neurologic function. Witnessed cardiac arrests in patients receiving high-quality CPR have better prognosis, with 25.5% of patients surviving to hospital discharge.
Cardiac arrest carries a dismal prognosis--most patients do not survive. In those that do survive, their hospital course can be complicated by varying degrees of neurologic injury due to hypoxic encephalopathy. All organ systems can suffer ischemic injury. Chest compressions when performed correctly can cause rib fractures, which may be complicated by pneumothorax.
In the event of cardiac arrest, the patient's family and/or their surrogate or power of attorney should be notified. It is important to ascertain the patient's code status, and any prior directives should be honored if appropriate documentation in accordance with laws of the local jurisdiction can be obtained.
By definition, infant CPR applies to patients whose age is less than one year. Child CPR applies to patients from one year of age through puberty. From puberty onward, adult CPR guidelines apply. The modifications for infant and child CPR are listed below. All other aspects of CPR follow the adult guidelines, including starting the process with the Compression first (CAB) sequence, and the rate of compressions being 100 to 120 per minute. The sternum should be depressed to a depth of approximately one-third of the anteroposterior diameter of the chest; this is about two inches in the child, and 1.5 inches in the infant. 
Child CPR Modifications
Chest compressions on a child are performed by placing the heel of one or two hands (depending on the size of the child) over the lower half of the sternum. The chest is compressed to a depth of approximately two inches, at a rate of 100 to 120 per minute. After 30 compressions, administer two sequential breaths and return to chest compressions. Continue the cycle of 30 compressions to two breaths until help arrives.
Infant CPR Modifications
Chest compressions on an infant are performed by placing two fingers on the sternum just below the nipple line. The infant's chest is compressed to a depth of approximately 1.5 inches, at a rate of 100 to 120 per minute. After 30 compressions, administer two sequential breaths and return to chest compressions. Continue the cycle of 30 compressions to two breaths until help arrives.
In the hospital setting, multiple rescuers are generally available, and ventilation is usually performed with a bag-valve-mask (BVM) device. BVM ventilation needs to be performed by a provider skilled in its use. If the patient is not intubated, CPR is done by one provider performing chest compressions, while the second provider provides breaths with BVM ventilation. The ratio of compressions to breaths in this situation changes to 15 compressions to two breaths. Once a patient is intubated, it is unnecessary to perform cycles of compressions and ventilation--chest compressions are performed continuously, while rescue breaths are given independently via the BVM at a rate of 10 per minute (one breath every six seconds). Novice operators frequently tend to provide BVM ventilations at a higher rate than this.
All healthcare workers including nurses and pharmacists must know how to perform CPR. In fact many hospitals now make it mandatory that healthcare workers have a valid CPR certificate in order to work. When done promptly and properly, CPR can save lives.
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