Update on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Guidelines

Peter J. Zed; Riyad B. Abu-Laban; Michael Shuster; Robert S. Green; Richard S. Slavik; Andrew H. Travers

Disclosures

Am J Health Syst Pharm. 2008;65(24):2337-2346. 

In This Article

CPR and Defibrillation

Compression: Ventilation Ratio

The 2005 CPR guidelines place an increased emphasis on chest compressions and recommend a compression:ventilation (C:V) ratio of 30:2, compared with 5:1 in 1992 and 15:2 in 2000.[4,5] Regardless of the ratio, two major focuses of the guidelines are the provision of timely and effective chest compressions and mitigation of hands-off time. The guidelines also address the need to simplify teaching, promote learners' skill retention, and address the social concerns with administering mouth-to-mouth resuscitation.

Multiple factors influence the effectiveness of CPR in restoring and maintaining coronary perfusion pressure (CPP), including the number of compressions and ventilations delivered in a given time period, the frequency with which compressions are interrupted, and the duration of interruptions.[7,8,9,10,11] Interrupting compressions to ventilate or perform other interventions negatively affects CPP. Each time the rescuer stops compressions to ventilate, CPP drops to baseline.[12,13] Results of studies have revealed that the interruption in compressions produced by two ventilations is approximately 15 seconds.[14,15,16] These findings are consistent with those of three studies conducted with patients in cardiac arrest, which demonstrated that compressions were not performed during 24-55% of each minute.[17,18,19] Eftestol et al.[20] examined rhythm strips recorded during VF cardiac arrest in human subjects, paying particular attention to the interval after defibrillation when no compressions were performed. During 634 no-compression intervals, ranging up to 20 seconds in length, the VF waveform deteriorated progressively, resulting in a decreased likelihood of successful defibrillation during subsequent attempts. When CPR is resumed after a pause to ventilate, several compressions are required to reestablish a minimally adequate CPP.[12,13]

It was previously assumed that ventilation was beneficial to outcome; however, the amount of ventilation required during CPR is unknown.[21] Animal studies have indicated that cerebral perfusion pressure and CPP are reduced with each positive-pressure ventilation.[12,22] High rates of ventilation via endotracheal tube significantly increase intrathoracic pressure and decrease organ perfusion during CPR and have been shown to be deleterious in animal cardiac arrest models.[23,24] Continuous chest compressions with no ventilation produce superior survival compared with compressions with ventilations at various C:V ratios in animal models with an open airway; however, when the airway is obstructed, virtually all animals not receiving ventilation die.[25,26] In a prospective, randomized human trial of dispatcher-assisted CPR, the intervention group received "chest compression only" instruction, and the control group received standard CPR instruction. The difference in survival rates was not significant between groups, with survival rates of 14.6% and 10.4% in the intervention and control groups, respectively.[27]

C:V ratios of 100:0, 100:2, 50:2, 50:5, 30:2, 15:2, 10:1, and 5:1 have received limited study with mixed results.[12,13,22,25,26,28,29,30,31,32,33] Rescuer fatigue with high rates of continuous compression may be a limiting factor.[30] In a single animal study when the airway was partially obstructed, a ratio of 30:2 was associated with a significantly shorter time to the return of spontaneous circulation (ROSC) and greater systemic and cerebral oxygenation versus continuous chest compressions.[26] Finally, one theoretical analysis of various C:V ratios suggests 30:2 provides the best blood flow and oxygen delivery while a second similar study found continuous compressions to be most effective for the first two minutes of CPR but 15:2 or 50:5 to be best thereafter.[29,34] Since the publication of the 2005 guidelines, the results of one combined animal and manikin study strongly support the hypothesis that a C:V ratio of 30:2 is superior to 15:2.[35]

Two human studies of different C:V ratios have also been published since the 2005 guidelines were released. The first instituted a continuous compression (no ventilation) protocol and compared outcomes with those from three years prior. The results were significantly better, with a 57% survival rate compared with 20% before protocol implementation (p = 0.001).[36] A prospective, multicenter, observational trial conducted in Japan found that in patients with apnea, cardiac-only resuscitation (no ventilation) resulted in a higher percentage of patients with favorable neurologic outcomes (6.2%) compared with patients receiving conventional CPR (3.1%) (p = 0.0195).[37]

Early Defibrillation

Although survival is clearly linked to the timing of defibrillation for VF (improved survival with earlier defibrillation), recent evidence has indicated that CPR before defibrillation may be beneficial. The 2005 CPR guidelines[4,5] incorporated current knowledge on defibrillation timing by recommending that Emergency Medical Service (EMS) rescuers give two minutes of CPR before defibrillation when the response interval (from call to arrival) exceeds four to five minutes and EMS responders did not witness the arrest. It is still recommended that lay rescuers use an automated external defibrillator (AED) as soon as possible.

For every minute defibrillation is delayed after VF onset, the rate of survival decreases by 7-10%.[38,39] Performing CPR during this delay interval slows the rate of survival decline to 3-4% per minute.[39,40] When responding to a cardiac arrest, there is some controversy about whether to initiate defibrillation before or after chest compressions. Current evidence suggests that immediate defibrillation should occur in the event of a witnessed cardiac arrest. However, if there is a delay greater than four to five minutes, it appears that defibrillation success is improved if CPR is provided first. In animal studies of VF lasting more than five minutes before treatment, providing CPR before defibrillation improved hemodynamics and survival rates.[41,42,43,44,45] In a human observational before-and-after study, a significant increase in survival was seen when EMS provided 90 seconds of CPR before defibrillating, rather than defibrillating without providing CPR (odds ratio [OR], 1.42; 95% confidence interval [CI], 1.07-1.90; p = 0.02).[46] A randomized controlled trial compared an EMS protocol providing three minutes of CPR before defibrillation to a protocol focused on immediate defibrillation and found no difference between the protocols when defibrillation was provided within five minutes; however, when the time from collapse exceeded five minutes, survival to hospital discharge was significantly greater in patients assigned to the "CPR first" protocol (OR, 6.79; 95% CI, 1.42-31.4; p = 0.01).[47] One randomized trial that did not factor delay time into the analysis found no benefit to CPR first when 90 seconds of predefibrillation CPR was compared with immediate defibrillation.[48]

While both animal and human data suggest that a protocol incorporating CPR before defibrillation will improve survival in certain circumstances, the most effective approach has not yet been established.

One-shock Versus Three-shock Sequence

The 2000 guidelines suggested that for treatment of cardiac arrest with a "shockable" rhythm, rescuers deliver up to three "stacked" shocks without CPR between the shocks and recheck the rhythm before and after each shock.[6] The 2005 guidelines evaluated not only the number of shocks but the dose, type (biphasic versus monophasic), duration, and sequence of defibrillation (immediate versus delayed). The major change in the 2005 guidelines was the recommendation for a single shock to be administered and followed immediately by CPR with no check of the cardiac rhythm until two minutes of CPR has been performed postdefibrillation. These recommendations were designed to minimize the interruptions in chest compressions and reflect the success of the first shock in eliminating VF by using biphasic waveforms.[4,5]

There is no direct evidence to suggest that one shock is superior to three stacked shocks. The rationale for single shocks is based on three major findings. First, the rhythm analysis used by AEDs after each shock results in an average delay of 37 seconds before the delivery of the first postshock chest compression.[49,50] As discussed above, this delay results in low CPP and is a predictor of poor survival.[12,13] Second, with a first-shock efficiency of 90% for biphasic defibrillators, stacked shocks provide little incremental value and unduly delay chest compressions.[20,49,50,51] In cases where the first shock fails, resumption of CPR confers greater benefit than further defibrillation.[51] Third, even when a shock eliminates VF, it may take several minutes for a heart rhythm to establish and even longer to achieve perfusion. Chest compressions can provide coronary and cerebral perfusion during this period. To defibrillate an adult with a monophasic defibrillator, the recommended energy is 360 J. The optimal defibrillation dose using a biphasic defibrillator is 150-200 J for a biphasic truncated exponential waveform or 120 J for a rectilinear biphasic waveform. The second dose, given after two minutes of CPR, should be 120 J or higher.[4,5]

Public-access Defibrillators

Optimal care in the prehospital setting involves bystander CPR and minimizing the time to defibrillation.[52] The 2005 guidelines recommend that AEDs should be implemented in public locations where there is a relatively high likelihood of witnessed cardiac arrest (e.g., airports, casinos, sport facilities).[4,5] A large prospective, community-based, multicenter clinical trial was conducted with 19,000 volunteer responders from 993 community units in 24 North American regions. The community units were randomly assigned to a structured and monitored emergency response system involving lay volunteers trained in CPR alone or in CPR plus the use of AEDs. The study found more survivors to hospital discharge in the units assigned to volunteers trained in CPR plus AEDs (relative risk, 2.0; 95% CI, 1.07-3.77; p = 0.03).[52]

Unfortunately, there are significant problems with the development and implementation of public-access defibrillator (PAD) programs. First, over 80% of cardiac arrests occur in homes. Second, accurate identification of community units at risk of cardiac arrest is difficult. Third, despite public perceptions, it is not necessarily the simple deployment of AEDs that will save lives, but rather the implementation and maintenance of AED programs embedded in a "chain of survival" program. Implementation guidelines must be provided to ensure optimal success from PAD programs.

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