The science driving BLS CPR recommendations

Recently, the American Heart Association released the new 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. We have explored the major clinical recommendations in AHA CPR Guidelines 2020. Now let’s dive into a more detailed glimpse into the science behind the BLS recommendations.

Before looking at the specific changes, it is important to mention the difference between recommendations made at the international level, recommendations made at the national level (by the American Heart Association), and recommendations made in the educational materials used in the actual courses.

International experts representing resuscitation councils from around the world continuously perform and publish systematic reviews of evidence about specific resuscitation-related topics [1].

The International Liaison Committee on Resuscitation (ILCOR) evidence review process eventually achieves consensus on the science and generates treatment recommendations based on the worldwide body of evidence.

Following a similar process, the American Heart Association assembles teams of resuscitation and education experts to work in conjunction with the ILCOR evidence review process to create resuscitation guidelines specifically for the American Heart Association audience [2].

With some resuscitation topics, no new evidence exists and a guideline writing team allows a previous recommendation to stand without any further comment. In other cases, the evidence may be so equivocal that a writing team can make no recommendation, either for or against the intervention. Finally, the product development teams at the American Heart Association must translate ILCOR and AHA science recommendations into practical applications for the students who attend one or more of the basic or advanced training programs.

Although there may be general scientific support for an action one must perform during a resuscitation attempt, there may not always be scientific support for the way the instructional materials demonstrate that action. As an example, the AHA CPR Guidelines 2020 make a strong recommendation for placing one hand on top of the other to perform adult chest compressions [3]. AHA CPR Guidelines 2020 do not make a recommendation of whether rescuers should interlock their fingers, even though there may be some practical advantages to doing so. As the videos for the training courses shows rescuers performing compressions, someone (or some group) within the product development team must instruct the actors on how to perform the skill on camera. Thus, a video might show actors performing a recommended procedure (chest compression) in a way that ILCOR or the AHA Guidelines development teams did not explicitly recommend (interlocked fingers).

Adult chain of survival

Although the concept of an integrated approach to caring for patients during the post-cardiac arrest phase first entered the adult chain of survival in 2010 [4], the AHA CPR Guidelines 2020 extends this focus by adding a new link to the chain, which targets the recovery and survivorship after cardiac arrest [3].

While it may be easy to imagine the physiologic toll cardiac arrest takes on an individual’s body, there may be additional mental and emotional tolls for those who survive. Anxiety, depression, and post-traumatic stress are common for patients who survive a cardiac arrest [5-8]. The survivor’s family members may experience similar stressors even one year after the event [9,10].

Psychosocial therapy provided in the first 15 months following out-of-hospital cardiac arrest significantly reduces the two-year cardiovascular mortality risk for survivors, although the mechanism for this reduction remains unexplained [11]. The recovery and survivorship link focuses on the need for hospital discharge plans to include the treatment, surveillance and rehabilitation needs of all survivors of cardiac arrest, which includes both the patients, their families and the caregivers [12].

Beginning resuscitation efforts

The basic sequence for adult CPR remains unchanged from the recommendations made in the 2015 guidelines update [13]. Whereas AHA CPR Guidelines 2010 commented on the reasonableness of beginning the resuscitation sequence with chest compressions (C-A-B) rather than opening the airway (A-B-C) [14], AHA CPR Guidelines 2020 more strongly support that recommendation, based on limited data [3].

AHA CPR Guidelines 2020 moderately reaffirm the value of including assisted ventilation in the CPR sequence for most victims of cardiac arrest, although the AHA continues to base this recommendation on limited data. However, the AHA acknowledges that healthcare providers generally have enough knowledge to tailor the initial resuscitation approach and may begin the sequence with airway control and ventilation, depending upon the circumstances surrounding the cardiac arrest.

Chest compression mechanics remain basically unchanged from AHA CPR Guidelines 2015. Based on expert opinion, you should generally perform CPR where the victim is found, as long as it is safe to do so. CPR is likely more effective if the patient is lying supine on a firm surface, although there is only limited data to support this recommendation. Manikin studies of simulated in-hospital resuscitations demonstrate only marginal increases in compression depth associated with placing a backboard between the patient and the mattress [15]. Likewise, limited data support a recommendation for placing the hands on the lower half of the sternum when performing chest compressions. Manikin studies do not support dominant over non-dominant hand placement against the sternum [16,17]. Finally, there is a reaffirmation of a weak recommendation from the AHA CPR Guidelines 2010 for healthcare personnel to perform CPR on patients is a prone position when it is not possible to place them in a supine position. While the efficacy of prone-positioning CPR is unknown, limited evidence from in-hospital cardiac arrest cases suggests it may be better than not providing CPR at all [18].

Compression depth and rate

While not altering current recommendations for compression depth and rate in adult patients, AHA CPR Guidelines 2020 reaffirm the importance of chest compression quality in achieving improved survival measures. Although the optimal chest compression depth remains unknown [19], the AHA continues to make a strong recommendation for chest compressions of at least two inches but not more than 2.4 inches in the adult patient, based on moderate-quality evidence. Similarly, the optimal compression rate for adults remain unknown [19]. One observational study found compression rates between 100 and 119 improved survival to hospital discharge rates for out-of-hospital cardiac arrest when compared to rates below 100 and rates between 120 and 139 [20].

On the other hand, an in-hospital observational study found the greatest likelihood of ROSC occurred with chest compression rates between 121 and 140 compared to rates lower than 121 or higher than 141 [21]. Consequently, AHA CPR Guidelines 2020 make a moderate-strength recommendation for compression rates of 100-120 compressions per minute, based on moderate-quality evidence. Finally, animal models demonstrate an association between incomplete chest wall recoil (leaning) during CPR and increases in intrathoracic pressure and decreases in coronary perfusion pressure [22,23]. Thus, based on limited data, AHA CPR Guidelines 2020 make a moderate-strength recommendation for healthcare providers to avoiding leaning on the chest during CPR.

Interrupting chest compressions

Two decades ago, animal models demonstrated adverse hemodynamic effects associated with interruptions in chest compressions, even for seemingly important reasons [24]. Subsequent research identified the chest compression fraction, which is the proportion of time rescuers spend delivering chest compressions during the resuscitation attempt [25]. For out-of-hospital cardiac arrest, improving the chest compression fraction results in increased rates of ROSC [26] and neurologically favorable survival [27]. Although an AHA expert consensus position is that resuscitation teams can achieve a chest compression fraction of 80% under a variety of conditions, [28], AHA CPR Guidelines 2020 make a weak recommendation (based on limited data) that it is reasonable to target a chest compression fraction of at least 60%.

One area of significant concern is the peri-shock pause, which is the interruption of chest compressions before, during, and immediately after defibrillation attempts [29]. Shorter rather than longer peri-shock pauses are associated with significantly higher odds of survival [30]. Single prolonged pauses in chest compressions, such as those associated with defibrillation attempts, may be more harmful than multiple short pauses, even when chest compression fractions are similar [31].

To help reduce interruptions in chest compressions and increase the chest compression fraction, AHA CPR Guidelines 2020 reaffirm the strong recommendation made in 2015 to keep pre- and post-shock compression pauses as short as possible. You should also limit pulse and rhythm checks to no more than 10 seconds. Unless you are absolutely sure a pulse is present following that check, resume chest compressions. As deterioration in chest compression quality appears about 90 to 120 seconds into a CPR cycle [32], AHA CPR Guidelines 2020 reaffirm the moderate recommendation made in 2010 to switch compressors every two minutes (or sooner, if fatigued) to maintain high-quality compressions. For patients in cardiac arrest without an advanced airway in place, it is reasonable for you to interrupt compressions briefly to deliver two breaths, each over a period of 1 second.

CPR feedback and monitoring

The AHA first mentioned the value of using performance feedback device to improve the quality of CPR back in 2005, although there was no formal recommendation at the time [33]. ILCOR acknowledges considerable debate on whether to continue the 2010 recommendation [14] for use of these devices, based in part on the lack of evidence demonstrating a significant association between real-time feedback and improved patient outcomes [34]. Given that the available evidence did not demonstrate a harm associated with the use of the devices, AHA CPR Guidelines 2020 make a weak recommendation to incorporate real-time feedback devices into the resuscitation event for use to help optimize CPR performance.

Along a similar vein, monitoring certain physiologic parameters can provide real-time information about the quality of the resuscitation efforts, which provides the rescue team an opportunity to correct deficiencies and improve the outcome. As an example, in-hospital end-tidal carbon dioxide or arterial blood pressure monitoring resulted in higher ROSC rates compared to no physiological monitoring, although survival to hospital discharge and survival with favorable neurological outcome were not different between the two groups [35]. As a result, AHA CPR Guidelines 2020 make a new but weak recommendation for the use of physiologic parameters as a guide to improve CPR quality.

Recommendation for cough CPR

Without citing any evidence or making any recommendations, AHA CPR Guidelines 2000 suggested that intrathoracic pressure increases associated with coughing could generate enough cerebral blood flow to maintain consciousness [36]. AHA CPR Guidelines 2005 elaborate by noting that consciousness associated with the technique typically lasts no more than 90 seconds [37]. ILCOR makes a strong recommendation against the routine use of cough CPR and a weak recommendation for in-hospital use as an early temporizing measure when a non-perfusing rhythm occurs but before the patient loses consciousness [34]. AHA CPR Guidelines 2020 echo that weak recommendation, although does not expressly limit cough CPR to in-hospital use.

Without any major changes at the BLS level, AHA CPR Guidelines 2020 continue to emphasize the importance of high-quality CPR. Early recognition of the cardiac arrest and prompt CPR beginning with chest compressions provides the best chances for survival for those who suffer an out-of-hospital cardiac arrest.

• Continue to compress the chest to a depth of 2-2.4 inches at a rate of 100-120 per minute and avoid leaning on the patient’s chest.
• Optimize CPR performance by incorporating real-time feedback devices into the resuscitation event.
• Keep interruptions in chest compressions to a minimum and target a chest compression fraction of at least 60%.

References

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