Prove it: Performing CPR before rhythm analysis makes a difference in cardiac arrest outcome
This study could not find any significant outcome differences between patients who receive a brief period of CPR and those who receive a longer period of CPR before rhythm analysis.
By Kenny Navarro
Medic Williams is excited about his first day assigned to Rescue 3. After breakfast, he and Medic Cruz respond with Engine 14 to a report of an unconscious person. They arrive to find a 60-year-old male in cardiac arrest. There was no bystander CPR. Williams powers on the manual monitor/defibrillator and places the defibrillation pads on the patient's chest while the firefighters begin high-quality CPR. About 20 seconds after arrival, the first rhythm analysis reveals ventricular fibrillation (VF). Williams follows the local protocol and provides a 200-joule countershock. The firefighters immediately resume chest compressions. Cruz quickly establishes IV access. After the two-minute period of CPR, Williams confirms the presence of asystole.
For the next 20 minutes, the team provides high quality CPR and epinephrine at three-minute intervals. The patient remains asystolic and the end-tidal capnography readings never rise above 10 mm Hg. Cruz and Williams agree to terminate the resuscitation attempt.
Back at the station, the two medics discuss the resuscitation events. Williams states that the Medical Director for the private EMS agency he worked for before joining the fire department advocated a two-minute period of CPR before attempting to defibrillate. Her rationale was that medics had to "prime the pump" in unwitnessed cardiac arrest to make defibrillation attempts more successful. Williams wonders if the outcome would have been different if they had delayed the shock for two minutes while performing CPR.
For decades, the National Standard Curriculum (NSC) directed paramedics to quickly analyze a patient's ECG rhythm upon discovering cardiac arrest. When the analysis revealed a shockable rhythm, the NSC advocated an immediate countershock. However, some evidence suggests that a period of CPR delivered before a countershock would improve the likelihood of a successful conversion and subsequent outcome (Weisfeldt & Becker, 2002). In 2005, the American Heart Association recommended that EMS personnel consider providing a one and a-half to three-minute period of CPR before attempting defibrillation if the EMS response time was greater than four or five minutes (American Heart Association, 2005). Researchers with the Resuscitation Outcomes Consortium (ROC) tested whether timing of the first rhythm analysis influenced outcomes in adult patients who suffer out-of-hospital cardiac arrest (Stiell et al., 2011).
The investigation involved 10 ROC sites comprised of 150 EMS agencies in the United States and Canada. The analysis sample included all patients over the age of 18 years who suffered a non-traumatic out-of-hospital cardiac arrest and received some form of resuscitation attempt by EMS personnel. From this sample, researchers excluded cases where
- EMS personnel witnessed the onset of the arrest period,
- the patient suffered blunt, penetrating, or burn-related trauma,
- patients exsanguinated,
- the patient was visibly pregnant,
- the patient was a prisoner,
- patients wore an "opt out" bracelet, indicating their desire not to be enrolled in the research project,
- the patient had a valid DNAR
- police or lay responders performed the first ECG analysis, or
- non-ROC agencies provided the initial treatment.
After arriving on the scene and verifying the presence of pulselessness, rescuers would begin CPR and apply the self-adhesive defibrillation pads. For the early-analysis group, rescuers provided between 30 and 60 seconds of CPR before analyzing the patient's ECG rhythm. For the later-analysis group, rescuers provided three-minutes of CPR before analyzing the ECG rhythm. In either case, if the analysis revealed VF, rescuers would attempt defibrillation and follow standard treatment protocols for the duration of the resuscitation effort.
The primary outcome variable was survival to hospital discharge with satisfactory functional status. Researchers determined the functional status using a modified Rankin scale, which assigns a number value to patients based on their ability to perform common daily activities (Rittenberger, Raina, Holm, Kim, & Callaway, 2011). Lower scores represent more independent activity; Scores greater than 4 represent either severe disability or death.
Before enrollment, research statisticians performed a power calculation to determine how many patients they would need to enroll in order to detect a meaningful difference between the two groups if a difference really existed. To produce a 99.6% power to detect a 3% difference between the two groups, the researchers determined the need to enroll 13,239 patients.
Twenty-nine months after beginning the investigation, a data safety monitoring board recommended early termination of the trial citing futility, meaning that continued enrollment was not likely to change the outcome. As a result, the researchers only enrolled 10,365 patients. Of these, the researchers had to exclude 195 because the arrest did not have a cardiac origin. They excluded an additional 95 because of an inability to gather outcome data. Therefore, the analysis included 9933 cases.
When the trial ended, there were 5290 patients in the early-analysis group, with a median time to analysis of 42 seconds. The later-analysis group included 4643 patients with a median time to analysis of 180 seconds. Most of the baseline characteristics between the two groups were not statistically different. However, a few CPR quality and drug administration characteristics were statistically different (p < .05) between the two groups. The pause in chest compression following a defibrillation attempt was slightly shorter for the early-analysis group (8.4 seconds vs. 9.1 seconds). The early-analysis group also had a slightly slower chest compression rate (107.2 vs. 108.6), received less total epinephrine during the resuscitation attempt (3.5 mg vs. 3.7 mg), and was less likely to receive sodium bicarbonate (18.3% vs. 19.9%). In contrast, the chest compression fraction was slightly higher for the later-analysis group (.71 vs. .66). Chest compression fraction is the proportion of time spent performing chest compressions for patients in cardiac arrest (Christenson et al., 2009).
There was no statistical difference between the early-analysis group and the later-analysis group with respect to the primary outcome variable (5.9% vs. 5.9%, respectively; p = .59). Secondary outcome variable analysis also could not demonstrate any statistical difference between the two groups with respect to the presence of a pulse on arrival at the emergency department (25.6% vs. 26.2%, respectively; p = .44), survival to hospital admission (24.6% vs. 24.4%, respectively; p = .71), or survival to hospital discharge regardless of the Rankin score (8.1% vs. 8.0, respectively; p = .92).
What this means for you
In the 1980s, researchers in Seattle found the addition of automated external defibrillation into their two-tiered EMS system did not significantly alter overall survival rates (Weaver et al., 1988). Other cities in the United States reported similar results (Joyce, Davidson, Manning, Wolsey, & Topham, 1998; Kellermann et al., 1993; Martens, Calle, & Mullie, 1993; Schneider et al., 1994; Sweeney et al., 1998). A canine study conducted at the University of California at Los Angeles suggested that if a patient remained in VF for about seven and a-half minutes before anyone performed chest compressions, defibrillation was more successful if rescuers provided an intravenous dose of epinephrine and five-minutes of CPR before delivering the countershock (Niemann, Cairns, Shama, & Lewis, 1992). In response, EMS Medical Directors in Seattle altered their cardiac arrest protocol and required personnel to provide 90-seconds of CPR before attempting to defibrillate the patient. They observed a significant improvement in survival rates, although the authors noted a number of limitations to the generalizability of their results (Cobb et al., 1999).
Since that time, two clinical studies support a period of CPR before rhythm analysis and defibrillation. An early observational trial conducted by the Resuscitation Outcomes Consortium could not demonstrate improved survival for patients who suffered an out-of-hospital cardiac arrest when medics delayed defibrillation longer than 45 seconds to provide a pre-shock period of CPR (Bradley et al., 2010). However, subgroup analysis found a trend toward improved survival when EMS response times were longer than five minutes and medics provided up to 190 seconds of CPR before defibrillation. Subgroup analysis of a randomized trial in Norway found the odds of one-year survival were seven times greater for patients who received three minutes of CPR before the first defibrillation attempt when EMS response intervals were greater than five minutes (Wik et al., 2003).
In contrast, three clinical studies do not support this strategy. Researchers in Australia examined patients who suffered an out-of-hospital cardiac arrest and had EMS response intervals greater than five minutes (Baker et al., 2008). Patients presenting with VF who received three minutes of CPR before the first countershock did not have improved survival to hospital discharge rates compared to those who received immediate defibrillation. Researchers conducting a randomized trial in Western Australia with patients who suffered non-paramedic witnessed cardiac arrest could not demonstrate improved survival to hospital discharge rates when paramedics provided 90-seconds of CPR before defibrillation compared to immediate defibrillation (Jacobs, Finn, Oxer, & Jelinek, 2005). Even with significant reductions in both pre- and post-shock pauses, firefighters in Paris using automated external defibrillators could not demonstrate any survival advantage offered by a 60-second period of CPR before the first shock compared to an immediate shock strategy (Jost et al., 2010).
A meta-analysis of randomized controlled clinical trials published between 1950 and 2010 could not demonstrate survival advantages of providing between 60 and 180 seconds of chest compressions before the first defibrillation attempt compared to an immediate shock strategy for patients with out-of-hospital cardiac arrest (Meier et al 2010).
It is important to note that this study did not evaluate survival differences resulting from either early or later defibrillation in patients where EMS providers witnessed the onset of the cardiac arrest. In those patients, current American Heart Association guidelines continue to recommend that rescuers begin CPR immediately and use a defibrillator as soon as it becomes available (Link et al., 2010).
In over one-third of the cases, EMS personnel in the current study did not provide the first rhythm analysis within the target goals identified by the research team. Perhaps the research team would have found different results if it were possible to insure that every medic in these EMS agencies always performed the first analysis exactly at the same time interval after arrival on the scene in every case. However, out-of-hospital resuscitation attempts are complex events and this type of strict protocol adherence is not possible, a limitation the authors readily admit. Despite this limitation, the difference between the mean analysis period intervals was far enough apart to test the concept.
Another limitation in this study is the inclusion of cases where the patients presented in non-shockable rhythms. Shockable rhythms were present in only one-fourth of the cases. The first rhythm analysis for almost 50% of the patients in either group identified asystole. Since survival from asystole is rare (McNally et al., 2011), it seems unreasonable to expect a difference in outcome if medics identify asystole 150 seconds earlier or later. Although subgroup analysis of patients who presented in a shockable rhythm could not find a difference in survival between the two groups, reducing the sample to one-fourth of the original number of cases significantly reduces the ability of researchers to find differences when they truly do exist.
Researchers in this study could not find any significant outcome differences between patients who receive a brief period of CPR and those who receive a longer period of CPR before rhythm analysis. The 2010 American Heart Association guidelines recommend that after verifying the presence of pulselessness, rescuers begin CPR immediately while simultaneously preparing a defibrillator for use (Link et al., 2010). Those same guidelines state that the value of intentionally delaying defibrillation while performing a period of CPR remains unclear (Neumar et al., 2010).
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The author has no financial interest, arrangement, or direct affiliation with any corporation that has a direct interest in the subject matter of this presentation, including manufacturer(s) of any products or provider(s) of services mentioned.