Cardiopulmonary Resuscitation (CPR) 

Background

For patients with cardiac arrest, survival rates and neurologic outcomes are poor, though early appropriate resuscitation, involving cardiopulmonary resuscitation (CPR), early defibrillation, and appropriate implementation of post–cardiac arrest care, leads to improved survival and neurologic outcomes. Targeted education and training regarding treatment of cardiac arrest directed at emergency medical services (EMS) professionals as well as the public has significantly increased cardiac arrest survival rates.^[1]

CPR consists of the use of chest compressions and artificial ventilation to maintain circulatory flow and oxygenation during cardiac arrest. A variation of CPR known as “hands-only” or “compression-only” CPR (COCPR) consists solely of chest compressions. This variant therapy is receiving growing attention as an option for lay providers (that is, nonmedical witnesses to cardiac arrest events).

The relative merits of standard CPR and COCPR continue to be widely debated. An observational study involving more than 40,000 patients concluded that standard CPR was associated with increased survival and more favorable neurologic outcomes than COCPR was.^[2] However, other studies have shown opposite results, and it is currently accepted that COCPR is superior to standard CPR in out-of-hospital cardiac arrest.

Several large randomized controlled and prospective cohort trials, as well as one meta-analysis, demonstrated that bystander-performed COCPR leads to improved survival in adults with out-of-hospital cardiac arrest, in comparison with standard CPR.^{[3, 4, 5]} Differences between these results may be attributable to a subgroup of younger patients arresting from noncardiac causes, who clearly demonstrate better outcomes with conventional CPR.^[2]

The 2010 revisions to the American Heart Association (AHA) CPR guidelines state that untrained bystanders should perform COCPR in place of standard CPR or no CPR (see American Heart Association CPR Guidelines).^[6]

Of the more than 300,000 cardiac arrests that occur annually in the United States, survival rates are typically lower than 10% for out-of-hospital events and lower than 20% for in-hospital events.^{[7, 8, 9, 10, 11]} A study by Akahane et al suggested that survival rates may be higher in men but that neurologic outcomes may be better in women of younger age, though the reasons for such sex differences are unclear.^[12]

Additionally, studies have shown that survival falls by 10-15% for each minute of cardiac arrest without CPR delivery.^{[13, 14]} Bystander CPR initiated within minutes of the onset of arrest has been shown to improve survival rates 2- to 3-fold, as well as improve neurologic outcomes at 1 month.^{[15, 16]}

It has also been demonstrated that out-of hospital cardiac arrests occurring in public areas are more likely to be associated with initial ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT) and have better survival rates than arrests occurring at home.^[17]

This article focuses on CPR, which is just one aspect of resuscitation care. Other interventions, such as the administration of pharmacologic agents, cardiac defibrillation, invasive airway procedures, post–cardiac arrest therapeutic hypothermia,^{[18, 19, 20, 21]} the use of echocardiography in resuscitation,^[22] and various diagnostic maneuvers,^{[23, 24]} are beyond the scope of this article. For more information, see the Resuscitation Resource Center; for specific information on the resuscitation of neonates, see Neonatal Resuscitation.

American Heart Association CPR guidelines

In 2010, the Emergency Cardiovascular Care Committee (ECC) of the AHA released the Association’s newest set of guidelines for CPR. Changes for 2010 include the following^{[23, 25]} :

• The initial sequence of steps is changed from ABC (airway, breathing, chest compressions) to CAB (chest compressions, airway, breathing), except for newborns
• “Look, listen, and feel” is no longer recommended
• The compression depth for adults should be at least 2 inches (instead of up to 2 inches)
• The compression rate should be at least 100/min
• Emergency cardiac treatments no longer recommended include routine atropine for pulseless electrical activity (PEA)/asystole, cricoid pressure (with CPR), and airway suctioning for all newborns (except those with obvious obstruction).
• Post–cardiac arrest care is covered in a new section^[26]

Several studies that looked at the quality of CPR being performed in hospitals and by EMS systems found that providers often did not perform CPR up to the standards of the ECC guidelines.^{[27, 28, 29, 30]} Specifically, they found that providers were often deficient in both rate and depth of chest compressions and often provided ventilations at too high a rate. Other studies demonstrated the impact of inadequate rate and depth on survival.^[31]

The 2010 AHA guidelines state that untrained bystanders should perform COCPR (previous AHA guidelines did not address untrained bystanders separately).^[6]

Several studies concluded that stopping compressions in order to give ventilations may be detrimental to the patient’s outcome.^{[32, 33, 34]} While a bystander halts compressions to give 2 breaths, blood flow also stops, and this cessation of blood flow leads to a quick drop in the blood pressure that had been built up during the previous set of compressions.^[35]

Indications

CPR should be performed immediately on any person who has become unconscious and is found to be pulseless. Assessment of cardiac electrical activity via rapid “rhythm strip” recording can provide a more detailed analysis of the type of cardiac arrest, as well as indicate additional treatment options.

Loss of effective cardiac activity is generally due to the spontaneous initiation of a nonperfusing arrhythmia, sometimes referred to as a malignant arrhythmia. The most common nonperfusing arrhythmias include the following:

• VF
• Pulseless VT
• PEA
• Asystole
• Pulseless bradycardia

Although prompt defibrillation has been shown to improve survival for VF and pulseless VT rhythms,^[36] CPR should be started before the rhythm is identified and should be continued while the defibrillator is being applied and charged. Additionally, CPR should be resumed immediately after a defibrillatory shock until a pulsatile state is established. This is supported by studies showing that “preshock pauses” in CPR result in lower rates of defibrillation success and patient recovery.^[31]

In a study involving out-of-hospital cardiac arrests in Seattle, 84% of patients regained a pulse when defibrillated during VF.^[29] Defibrillation is generally most effective the faster it is deployed.

Contraindications

The only absolute contraindication to CPR is a do-not-resuscitate (DNR) order or other advanced directive indicating a person’s desire to not be resuscitated in the event of cardiac arrest.

A relative contraindication to performing CPR may arise if a clinician justifiably feels that the intervention would be medically futile, although this is clearly a complex issue that is an active area of research.^{[37, 38]}

Anesthesia

Because a person in cardiac arrest is almost invariably unconscious, anesthetic agents are not typically required for cardiopulmonary resuscitation (CPR).

Equipment

CPR, in its most basic form, can be performed anywhere without the need for specialized equipment. Regardless of the equipment available, proper technique (see Technique) is essential.

Universal precautions (ie, gloves, mask, gown) should be taken. However, in the vast majority of patients who are resuscitated in the out-of-hospital setting, CPR is delivered without such protections, and no cases of disease transmission via CPR delivery have been reported.

Some hospitals and emergency medical services (EMS) systems employ devices to provide mechanical chest compressions, although until relatively recently, such devices had not been shown to be more effective than high-quality manual compressions.^[39] A study has been published that shows increased survival with better neurologic outcome in patients receiving active compression-decompression CPR with augmentation of negative intrathoracic pressure, compared with patients receiving standard CPR.^[40]

Additionally, other health systems have begun to implement devices to monitor CPR electronically and provide audiovisual CPR feedback to providers, thereby helping them improve the quality of compressions during CPR.^{[31, 41, 42, 27]}

An Advanced Cardiac Life Support (ACLS) provider (ie, physician, nurse, paramedic) may also elect to insert an endotracheal tube directly into the trachea of the patient (intubation), which provides the most efficient and effective ventilations. However, 2 retrospective cohort studies have called into question the value of prehospital endotracheal intubation,^{[43, 44]} and further study in this area is warranted.

An additional device employed in the treatment of cardiac arrest is a cardiac defibrillator. This device provides an electrical shock to the heart via 2 electrodes placed on the patient’s chest and can restore the heart into a normal perfusing rhythm.

Positioning

CPR is most easily and effectively performed by laying the patient supine on a relatively hard surface, which allows effective compression of the sternum. Delivery of CPR on a mattress or other soft material is generally less effective.

The health care provider giving compressions should be positioned high enough above the patient to achieve sufficient leverage, so that he or she can use body weight to adequately compress the chest (see the video below).

In the hospital setting, where patients are in gurneys or beds, appropriate positioning is often achieved by lowering the bed, having the CPR provider stand on a step-stool, or both. In the out-of-hospital setting, the patient is often positioned on the floor, with the CPR provider kneeling over him or her.

Overview

In its full, standard for, cardiopulmonary resuscitation (CPR) comprises 3 steps: chest compressions, airway, and breathing (CAB), to be performed in that order in accordance with the 2010 American Heart Association (AHA) guidelines.

Note that artificial respirations are no longer recommended for bystander rescuers; thus, lay rescuers should perform compression-only CPR (COCPR). Healthcare providers, however, should perform all 3 components of CPR (chest compressions, airway, and breathing).

For an unconscious adult, CPR is initiated using 30 chest compressions. Perform the head-tilt chin-lift maneuver to open the airway and determine if the patient is breathing. Before beginning ventilations, rule out airway obstruction by looking in the patient’s mouth for a foreign body blocking the patient’s airway. CPR in the presence of an airway obstruction results in ineffective ventilation/oxygenation and may lead to worsening hypoxemia.

The techniques described here refer specifically to CPR as prescribed by the Basic Cardiac Life Support (BCLS) guidelines. In the in-hospital setting, or when a paramedic or other advanced provider is present in the out-of-hospital setting, Advanced Cardiac Life Support (ACLS) guidelines call for a more robust approach to treatment of cardiac arrest, including drug interventions, electrocardiographic (ECG) monitoring, defibrillation, and invasive airway procedures.

Attempting to perform CPR is better than doing nothing at all, even if the provider is unsure if he or she is doing it correctly. This especially applies to many people’s aversion to providing mouth-to-mouth ventilations. If one does not feel comfortable giving ventilations, chest compressions alone are still better than doing nothing.

Chest compression

The heel of one hand is placed on the patient’s sternum, and the other hand is placed on top of the first, fingers interlaced. The elbows are extended and the provider leans directly over the patient (see the image below). The provider presses down, compressing the chest at least 2 in. The chest is released and allowed to recoil completely (see the video below).

With the hands kept in place, the compressions are repeated 30 times at a rate of 100/min. The key thing to keep in mind when doing chest compressions during CPR is to push fast and hard. Care should be taken to not lean on the patient between compressions, as this prevents chest recoil and worsens blood flow.

After 30 compressions, 2 breaths are given (see Ventilation). Of note, an intubated patient should receive continuous compressions while ventilations are given 8-10 times per minute. This entire process is repeated until a pulse returns or the patient is transferred to definitive care.

When done properly, CPR can be quite fatiguing for the provider. If possible, in order to give consistent, high-quality CPR and prevent provider fatigue or injury, new providers should intervene every 2-3 minutes (ie, providers should swap out, giving the chest compressor a rest while another rescuer continues CPR).

For COCPR (ie, CPR without rescue breaths), the provider delivers only the chest compression portion of care at a rate of 100/min to a depth of 38-51 mm (1-1.5 in.) without pause. This delivery of compressions continues until the arrival of medical professionals or until another rescuer is available to continue compressions.^[3]

Ventilation

If the patient is not breathing, 2 ventilations are given via the provider’s mouth (see the image below) or a bag-valve-mask (BVM).

The mouth-to-mouth technique is performed as follows (see the video below):

• The nostrils of the patient are pinched closed to assist with an airtight seal
• The provider puts his mouth completely over the patient’s mouth
• The provider gives a breath for approximately 1 second with enough force to make the patient’s chest rise

  CPR ventilation. Video courtesy of Daniel Herzberg, 2008.

Effective mouth-to-mouth ventilation is determined by observation of chest rise during each exhalation. Failure to observe chest rise indicates an inadequate mouth seal or airway occlusion. As noted (see above), 2 such exhalations should be given in sequence after 30 compressions (the 30:2 cycle of CPR). When breaths are completed, compressions are restarted. If available, a barrier device (pocket mask or face shield) should be used.

More commonly, health care providers use a BVM, which forces air into the lungs when the bag is squeezed. Several adjunct devices may be used with a BVM, including oropharyngeal and nasopharyngeal airways.

The BVM or invasive airway technique is performed as follows:

• The provider ensures a tight seal between the mask and the patient’s face.
• The bag is squeezed with one hand for approximately 1 second, forcing at least 500 mL of air into the patient’s lungs.

Next, the provider checks for a carotid or femoral pulse. If the patient has no pulse, chest compressions are begun.

Complications

Performing chest compressions may result in the fracturing of ribs or the sternum, though the incidence of such fractures is widely considered to be low.

Artificial respiration using noninvasive ventilation methods (eg, mouth-to-mouth, bag-valve-mask [BVM]) can often result in gastric insufflation. This can lead to vomiting, which can further lead to airway compromise or aspiration. The problem is eliminated by inserting an invasive airway, which prevents air from entering the esophagus.