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CPR for Prehospital Providers

Todd M. Cage MEd, NRP

Introduction

Cardiopulmonary resuscitation (CPR) has been a mainstay in the treatment of sudden cardiac arrest since the 1950s.1,2 The purpose of CPR is to maintain perfusion of oxygenated blood to the patient who is pulseless and apneic. This has historically consisted of compressing the chest and providing artificial ventilation.3 Defibrillation, which consists of sending an electronic shock through the heart to stop arrhythmia, was merged with CPR in the 1990s, when technological advances allowed for automated external defibrillators (AEDs) to be placed in public settings, such as airports, casinos, schools, golf courses, and malls.4

Procedures

In current practice, the term high-quality CPR is used to describe the ideal performance of this basic yet essential part of cardiac arrest management.5 First proposed in a 2013 American Heart Association (AHA) Consensus Statement, the components include ensuring compressions are performed at an adequate rate and depth while allowing for full chest recoil. Further, rescuers minimize interruptions in chest compressions and avoid excessive ventilations.6,7 The principles of high-quality CPR are valid for patients of all ages, with slight differences in depth and technique for infants and small children.

Compressions

In the patient without a pulse, chest compressions are the key to maintaining the circulation of blood to the tissues. Several human studies indicate that the chance for successful defibrillation with return of spontaneous circulation (ROSC) decreases in periods without chest compressions.6,8 Current guidelines instruct the rescuer to bare the chest and place the heel of one hand in the middle of the patient’s chest, which is the lower half of the sternum, and the heel of the other hand on top of the first. The hands should overlap and be parallel to each other.5,9 A study on perceptions of hand placement found that 79% of respondents would not expose the chest prior to starting compressions. The most common (40%) reason for this was the thought that effectiveness was the same. This is concerning because an exposed chest makes it easier to locate the correct hand position and apply defibrillator pads.10 Two recent manikin studies explored the use of the dominant hand in CPR. Both studies found that the quality of CPR was improved when the rescuer’s dominant hand was placed on the sternum. Although these studies are preliminary, they provide an interesting avenue for researchers looking to improve the effectiveness of chest compressions.11,12

In the patient with an unprotected airway, the guidelines call for chest compressions and ventilations to be performed at a ratio of 30:2 with pauses in compressions being limited to 10 seconds. A total of five cycles of compressions and ventilations makes up the two minutes that resuscitation is based on.5 One observational study theorizes that the change to the two-minute framework increases the chance of survival of patients who presented with non-shockable rhythms, such as asystole and pulseless electronic activity (PEA).13 The time frame when compressions are not being performed is called hands-off time.5,9 The proportion of time spent delivering compressions versus hands-off time is known as the chest compression fraction (CCF). Data from the Resuscitations Outcome Consortiums (ROC) trial indicate that increasing CCF is an independent predictor of survival in patients who suffer a prehospital ventricular fibrillation/tachycardia cardiac arrest.14 The 2015 guidelines recommend a target CCF of at least 60% and the belief that CCF of 80% is achievable in high performance systems. A cluster-randomized crossover trial from the ROC group explored whether continuous chest compressions with unsynchronized ventilations in the unprotected airway would provide better outcomes than traditional interrupted chest compressions. The study found that continuous chest compressions did not result in significantly higher rates of survival of neurological outcomes.15

Although it is easy to focus on hands-off time caused by ventilator efforts, a three-year study from Norway found that pauses for ventilation account for only a fraction of the no-flow time. Long pauses resulting from obtaining intravenous access, analyzing rhythms, and performing intubation, in addition to managing the scene, are also of concern.16,17

Rate: The rate of compression has progressively increased over time since the release of the 1980 AHA guidelines, Standards and Guidelines for Cardiopulmonary Resuscitation (CPR) and Emergency Cardiac Care (ECC).18 Throughout this century, the rate of at least 100 per minute has been part of the guidelines.9,19,20

Studies of healthcare worker performance have found that compression rate can be below or higher than that recommended by the guidelines.21-24 Suboptimal compression rate correlates to poor return of spontaneous circulation.25 A crossover trial of healthcare workers performing CPR at the rates of 100, 120, and 140 found the fractions of chest compressions with sufficient depth suffered at both the rates of 100 and 140. At the rate of 140, subjects were more likely to become fatigued quickly. Interestingly enough, the percentage of compressions with correct hand position was lowest at the rate of 100.26 Data from the ROC trial indicates that a range of 100–120 compressions per minute is optimal.27 The 2015 guidelines instruct rescuers to perform chest compressions within this range of 100-120 compressions per minute.5

Depth: The 2010 guidelines indicated that chest compressions in the adult patient should be at a depth of at least 2 inches, or 5 cm. This is an increase over previous recommendations for compression depths.9,20 A prospective review of cardiac arrests in Arizona found that mean compression depth was deeper in survivors (53.6 mm) than non-survivors (48.8 mm).26 Several studies have found that depth of compressions is typically too shallow to meet the guidelines. This is a cause for concern because the depth of compressions affects blood flow to the patient and intrathoracic pressure.21,24,29 A prospective, multi-center, observational study of adult cardiac arrest patients found that inadequate chest compression depth was associated with the failure of the defibrillatory shock.30 There is also an association between higher compression rates and lower compression depth.26,27,31 On the other end of the spectrum, some evidence suggests that some rescuers are able to perform compressions at an overly aggressive depth. Therefore, the 2015 guidelines adds a maximum depth of 2.4 inches, or 6 cm, to reduce the risk of injury from chest compressions.5

Full chest recoil: Full chest recoil occurs when the compressor allows the patient’s sternum to return to its natural position on the upstroke (decompression phase) of every chest compression. Incomplete chest wall release is commonly attributed to rescuers leaning on the chest during chest compressions, which reduces the ability of venous blood to return to the heart.32-34

It has been reported that a change in hand position may be needed to help rescuers achieve full chest recoil, but more research needs to be conducted to verify the optimal methods of obtaining recoil.35 There is also evidence that immediate compression feedback provided to rescuers by devices attached to the AED or cardiac monitor can improve full-chest recoil and other aspects of high-quality CPR.36

Injuries: Although life-saving, chest compressions are not without risk to the patient. A study of 170 patients treated by a hospital code team showed 32% of patients had iatrogenic trauma. Rib and sternal fractures accounted for greater than 50% of the injuries in this group, with a compression depth greater than 6 cm increasing the risk of injury.30,35,37 Studies of forensic records from Edinburgh show a similar pattern of injury among 499 subjects with 54% demonstrating injury to the chest wall, ribs or sternum.37 Studies have also indicated the possibility of injury to the heart, lungs, spleen, and abdomen, although those injuries are less common.37,39-42

Historically, studies of CPR injury have been autopsy studies or studies of post-resuscitation chest radiographs. There is concern that this leads to underreporting because chest x-rays can miss minor injuries. An evolving practice taken from the trauma literature involves multi-detector computed tomography (MDCT). A study by Sueng compared out-of-hospital cardiac arrest (OHCA) patients to those who were in-hospital. Patients who were older, experienced their arrest out-of-the hospital and had longer CPR times were associated with injury. Although this study had some limitations, it is noteworthy that only 11 of 138 patients had serious complications (i.e., pneumoperitoneum, hemoperitoneum, massive subcutaneous emphysema, tension pneumothorax, or haemomediastinum). All patients in this study survived to hospital discharge.43

Ventilations

In 1958, Dr. Peter Safar showed that expired air resuscitation will maintain adequate cerebral perfusion of oxygenated blood.3 Ventilations can be performed by mouth-to-mouth, mouth-to-mask/barrier device, or bag-valve mask. Pauses in chest compressions to deliver ventilations should take less than 10 seconds.

Volume: Adult CPR tidal volumes of approximately 500–600 mL (6 to 7 mL/kg) are recommended and can be described as producing a visible chest rise. Each ventilation or breath should take no longer than one second, and students in BLS classes are evaluated to ensure that less than 10 seconds of hands-off time is used.7 Evidence suggests that a single rescuer would have more trouble attaining this standard than a multiple rescuer situation in which tasks are shared. A prospective study of out-of-hospital providers from the Netherlands found that rescuers are generally able maintain to the hands-off time standard in the patient with the unprotected airway.44

Rate: Several years of research have shown that healthcare workers tend to hyperventilate the patient in cardiac arrest.24,45-47 Aufderheide and Lurie found that paramedics often hyperventilated patients even after retraining. This discovery led them to study the effect of hyperventilation in a porcine model. Their research found that hyperventilation decreased coronary perfusion pressures and survival rates by 69%.48 In the unprotected airway, the ventilation rate is two breaths given during the pause after each 30 compressions. In the patient with an advanced airway in place, the recommendation is to ventilate one breath every 6 seconds.5

Defibrillation

Defibrillation has been regarded as an important treatment for cardiac arrest caused by ventricular fibrillation since 1947.17 The purpose of the defibrillatory shock is to stop all electrical activity in the heart with the hope that the normal pacemaker will regain control of the cardiac conduction system.49 Successful termination of ventricular fibrillation by transthoracic defibrillation depends on delivery of sufficient current. Current flow is determined by the shock energy delivered and by the transthoracic impedance (TTI) encountered. TTI depends on multiple factors, including chest size, electrode chest wall interface (i.e., contact pressure), electrode area, and edge length.50

Defibrillation can be performed with either a manual defibrillator or an AED. The shock from a manual defibrillator can be applied using paddles or adhesive pads. Paddles require a conductive gel or pad to be used on the patient. The healthcare worker must also use firm pressure to each paddle to maximize contact with the patient’s chest. Healthcare workers need to apply 12 kg (25 pounds) of paddle force against the chest wall to be effective.51

The use of defibrillator electrode pads was introduced in the mid-1980s, and their popularity increased as AED use became more widespread. Early studies showed that shocks were delivered more quickly and were effective at terminating ventricular fibrillation when using adhesive pads with manual defibrillators.51-53 Garcia and Kerber evaluated multiple pad positions and found that each provided acceptable TTI to terminate ventricular fibrillation.50

Current AHA guidelines reference the following four pad positions:

  • Anterolateral;
  • Anteroposterior;
  • Anterior-left infrascapular, and
  • Anterior-right infrascapular.55

Bi-phasic vs. monophasic: Traditional defibrillators used a monophasic waveform to deliver a shock to the heart. Most current defibrillators are being produced with a biphasic waveform. These defibrillators are categorized in one of the following three ways:

  • Rectilinear biphasic;
  • Biphasic truncated exponential (BTE), and
  • Impedance-compensated biphasic truncated exponential.

Monophasic external defibrillators were developed by William Kouwenhoven in the 1950s.2 With the monophasic wave form, the shock emanates in one pad/paddle and travels through the body to the other pad/paddle. Biphasic waveform defibrillators tend to use a lower energy than monophasic waveform defibrillators while producing the same or better success in terminating ventricular fibrillation. With biphasic defibrillators, the shock passes through the patient twice, which results in a longer period of energy in the heart.56-59 Each vendor uses a proprietary waveform. This means there is no specified dose in the AHA guidelines; rather the manufacturer dictates the dose.

Although most defibrillators will be biphasic, it is still appropriate to use a monophasic defibrillator if that is what is available to you. Evidence from a large registry in Japan indicates no statistical difference in ROSC and one-month survival with limited neurological impairment between monophasic and biphasic defibrillators.60

Timing: Defibrillation is the treatment of choice in ventricular fibrillation and pulseless ventricular tachycardia. A review of a large, single-state registry found that patients who received a defibrillatory shock within two minutes of their cardiac arrest were five times more likely to survive with favorable neurological outcomes than those who were defibrillated after 10 minutes of cardiac arrest. It is important to note that patients in this study who were defibrillated within five minutes of their cardiac arrest were most often defibrillated by bystanders with a public access AED or first responders.61 The incidence of these rhythms is decreasing.62,63

Researchers are attempting to determine methods of optimizing the defibrillatory shock when ventricular fibrillation is present. The first study was to determine if CPR prior to defibrillation was more effective than an initial defibrillation, which is what has been taught in the past. The largest of these studies was an evaluation of more than 10,000 patients from the ROC trial. This randomized control trial of 150 sites found no significant difference in outcome between the two groups. Although the chosen strategy is subject to medical control, the direction from this study is to begin CPR until the defibrillator is ready and apply the defibrillator as quickly as possible.64 This is an area of continued study because researchers believe improvements in technology may allow for rhythm-analysis algorithms that provide guidance on the best course of treatment for each patient.65,66

Current AHA guidelines call for limiting interruptions in CPR to no longer than 10 seconds, except for specific interventions like defibrillation.9 All defibrillators currently available require CPR to be stopped before analyzing rhythms. The time period when CPR is stopped for the rhythm analysis and shock phase of the defibrillator is called the peri-shock pause. This time does not end until compressions are resumed (e.g., post-shock pause).

Data from the ROC trial discovered that the peri-shock pause is an independent variable of cardiac arrest survival.67 The study found that the odds of survival were lower if the peri-shock pause was greater than or equal to 40 seconds. It also found that every five- second increase in peri-shock pause decreased survival by 18%. The best chance for survival existed when the peri-shock pause was less than 20 seconds.67 A separate multi-center trial found that the odds of successful defibrillation increase for every five-second decrease in pre-shock pause.30

A study from San Diego found that patients who experienced less than 3 seconds of pause prior to the shock and less than 6 seconds post shock had higher likelihood of ROSC.68 A retrospective review of OHCA data from one of the ROC sites indicates that compressions during the charging of the defibrillator resulted in an increase in CCF.69

Because rhythm analysis time is part of the peri-shock period, the solution lies in part with the vendors of AEDs. Work is ongoing to adjust the algorithms and charging mechanisms of AEDs to reduce this time period.70

A second option is to allow trained personnel to use the manual feature of the defibrillator, rather than continuing in AED mode.71,72 Simulation-based studies are exploring whether changes to the protocol, such as pre-charging the defibrillator or adjusting tasks like who pushes the shock button, can decrease the peri-shock pause.73,74 Although these studies are promising, a clinical trial demonstrating these changes has not yet been published.

A possibility that is undergoing study is to explore whether the rescuer can be “grounded” against the shock through the use of exam gloves, thus allowing CPR to continue during the shock.

Initial studies show that standard exam gloves do not provide adequate insulation against the electrical shock delivered by an AED.73,75-77 More research into “hand-on defibrillation” is ongoing.

Bystander CPR

Early CPR is the second link in the American Heart Association (AHA) chain of survival. Data from the multi-center Cardiac Arrest Registry to Enhance Survival (CARES) system indicates that patients who received bystander CPR had a higher rate of survival (11.2%) than those who did not receive bystander CPR (7.0%).78

Despite efforts at public education, rates of bystander CPR remain low in many locales and are credited with lower survival rates.79 Fear of infectious disease transmission is the most common reason posited for why bystanders might be reluctant to perform CPR.80 Additionally, the rates of bystander CPR are lower in communities of color, who also have higher rates of cardiac arrest. Recently, the High Arrest Neighborhoods to Decrease Disparities in Survival (HANDDS) program was developed in Denver to promote community change. This program is being piloted in four major metropolitan areas.81

Current guidelines call for teaching the lay rescuer chest compressions-only CPR (CCCPR) or hands-only CPR.5 Hands-only CPR is keeping with recommendations that simplified CPR will be easier to learn and perform and that avoiding instruction of rescue breathing with speed the initiation of chest compressions.80 In addition, dispatch centers that provide pre-arrival instructions to callers use compressions-only CPR. A two center randomized trial comparing the compressions-only CPR to traditional CPR instruction shows that compressions-only CPR was associated with lower risk of death and higher short- and long-term survival.82 An observational study from Japan found favorable neurological outcomes in the compressions-only group when compared to the standard CPR group.83 An examination of All-Japan Utstein Registry from 2005–2009 finds that patients who received compressions-only CPR and a shock from a public-access AED prior to EMS arrival were more likely to experience ROSC and one-month survival with a favorable neurological outcome.84 Additionally, Heidenreich, et al found that students trained in compressions-only CPR have a higher retention rate as far as 18 months after training.85

Dispatcher-Assisted CPR

One method to improve bystander CPR has been the move toward dispatcher-assisted CPR. The 2015 guidelines call for dispatchers to identify the patient who is unresponsive with abnormal breathing or and agonal gasps and to provide chest compressions-only CPR instructions to callers.86 Although there is concern about the ability for dispatchers to assist callers in identifying the patient in cardiac arrest, two studies from large systems indicate the risks of performing bystander CPR on patients with a pulse is small.87,88

Cardiocerebral Resuscitation

There is a movement amongst some EMS systems to perform cardiocerebral resuscitation (CCR). This is being explored in an effort to increase survival rates from cardiac arrest. The tenets of CCR parallel the intentions of the guidelines because there is a focus on increasing rates of bystander CPR and decreasing interruptions in chest compressions.

The proponents of CCR also moved to a single shock prior to the release of the 2005 AHA Guidelines for CPR and Emergency Cardiac Care. The primary difference is an earlier move to continuous chest compressions with airway management completed with an oropharyngeal airway and a nonrebreather mask.89,90 The 2015 guidelines expect CCR to be used in EMS systems as part of a bundle of care.5

Conclusion

For patients in cardiac arrest, cardiopulmonary resuscitations are literally the difference between life and death. But there’s more to CPR than just compressing a patient’s chest. Although CPR is considered a basic procedure, the perfusion of oxygenated blood to the patient in cardiac arrest is a process of pronounced complexity. A great deal of research into CPR has been conducted over the past decades, and there is more work on the horizon as more emerges about how the human body functions. In the short term, the focus on high-quality CPR serves as the bedrock to effective resuscitation.

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Published: September 1, 2016
Revised: October 5, 2016