Prove It: Are continuous chest compressions more effective?
Resuscitation Outcomes Consortium (ROC) randomized, controlled trial compared interrupted CPR and continuous-chest-compression CPR
Rescue 12 and Engine 52 respond to a report of an unconscious person in a private residence. On the way, a dispatch indicates the patient is a 67-year-old male and one of the dispatchers is giving compression-only CPR instructions to the patient's wife over the phone.
Upon arrival, Engine 52 confirms the presence of cardiac arrest and takes over CPR from the patient’s wife. One of the firefighters applies and activates the AED, which advises a shock is necessary. After delivering the single shock, the firefighters resume high-quality CPR, delivering cycles of 30 chest compressions interrupted for a five-second period to deliver two breaths from a bag-mask device attached to an oxygen source.
Rescue 12 arrives and transitions the patient from the AED to a manual defibrillator. The cardiac monitor screen displays ventricular fibrillation. The engine lieutenant, who is functioning as the team leader, informs the rescue's paramedics the next shock is due in 30 seconds. Paramedic Rogers asks one of the firefighters not to stop chest compressions until it is time to defibrillate. He also instructs another firefighter to deliver a single, slow breath after every 10 compressions and not to try to synchronize the breath to a chest compression or recoil.
The second defibrillation shock is delivered on time. As the team resumes CPR, Rogers asks the team not to deliver a 30 to 2 compression/ventilation ratio. Instead, he wants them to perform continuous chest compression with the rate assisted by a metronome. He also asks one of the firefighters to squeeze the bag-mask device over a 1 to 2 second period only once after every 10 compressions. He instructs the team not to pause the chest compressions for any reason during the next two-minute cycle.
At the next rhythm check, the monitor screen displays an organized rhythm at a rate of about 68 complexes per minute. Rogers is able to detect the presence of a femoral pulse. The patient remains comatose and does not attempt to breath on his own. Paramedic Davis reports a blood pressure of 96/50 mm Hg. Rogers easily inserts an endotracheal tube and attaches waveform capnography. The patient remains stable throughout transport.
After transferring patient care to the emergency department, Rogers tells the crew from Engine 52 that he recently read an article that suggested continuous chest compression was a better way to perform CPR.
Researchers with the Resuscitation Outcomes Consortium (ROC) recently conducted a randomized, controlled trial in the out-of-hospital (OOH) setting to compare two methods of chest compression delivery during CPR . One group of patients, the interrupted CPR (I-CPR) group, received standard American Heart Association (AHA) CPR consisting of 30 chest compressions followed by a short pause during which EMS personnel delivered two breaths. The experimental group received continuous chest compression CPR (CCC-CPR). For this group, EMS personnel delivered 100 continuous chest compressions per minute. EMS personnel also delivered one breath after every 10 compressions; however, the compressor did not pause to allow other personnel to deliver the breath.
The primary outcome measure was the rate of survival-to-hospital discharge. Secondarily, the research team also measured neurological outcome using the modified Rankin scale, which grades the neurological status of the patient on a scale from 1 to 6 with lower numbers representing better neurological function .
Two previous trials conducted by the ROC found the rate of survival-to-hospital discharge for patients receiving I-CPR to be about 8.1 percent [3, 4]. The researchers thought CCC-CPR might improve those discharge rates by about 1 percent. In order to detect that difference between the two groups, the researchers estimated they would need to enroll about 23,600 patients.
Data analysis would only include cases in which the patient was over the age of 18 years and suffered a cardiac arrest in the OOH environment. A number of conditions would exclude the case from the final analysis. These conditions included:
- Cardiac arrest resulting from trauma or asphyxiation.
- The presence of uncontrolled exsanguination.
- EMS-witnessed cardiac arrest.
- The presence of a legal advanced directive instructing EMS personnel not to attempt resuscitation.
- Patients known or suspected to be pregnant.
- Patients with a preexisting tracheostomy.
- Patients known to be prisoners.
- Patients who received initial CPR from EMS agencies not participating in the study.
- Patients who received CPR with a mechanical chest compression device.
- Patients who had advanced airway insertion prior to the arrival of an EMS agency participating in the study.
- Patients who choose not to participate in the study.
During the four years it took to conduct the study, the research team closely monitored the CPR performance data of all the participating EMS agencies. At regular intervals, those agencies received CPR report cards that tracked how well each agency adhered to strict performance criteria. Agencies who did not achieve those performance goals could not submit cases for inclusion. However, if those agencies improved CPR performance and received passing grades by the next report card, they could resume enrolling cases again.
The final analysis included 12,613 patients who received CCC-CPR and 11,035 patients who received I-CPR. Patient and response characteristics such as whether the arrest was witnessed, whether a bystander provided CPR, and time from dispatch until arrival of EMS were not significantly different between the two groups. Characteristics of the resuscitation attempt, such as the time from EMS arrival until the start of CPR, presentation of a shockable rhythm, number of shocks delivered, and both intubation attempts and successes were not significantly different between the two groups.
However, as expected, patients in the CCC-CPR group had significantly higher chest compression fraction (83 percent vs. 77 percent, respectively) and fewer pauses in compressions greater than two seconds in duration (3.8 vs. 7.0, respectively) when compared to the group receiving I-CPR. Surprisingly, the mean average depth of chest compressions was deeper in the I-CPR group than for the CCC-CPR group (48 mm vs. 49 mm, respectively).
A significantly greater percentage of patients in the I-CPR group survived long enough to be admitted into the hospital when compared to the CCC-group (25.9 percent vs. 24.6 percent, respectively). Among those patients admitted into the hospital, there was no difference in the use of therapeutic hypothermia, coronary catheterization within 24 hours of ED arrival, or the insertion of an implantable defibrillator between the groups.
With respect to the primary outcome variable, which was the point of the entire study, there was no significant difference (p = .07) in survival to hospital discharge rates between the CCC-CPR group and the I-CPR group (9.0 percent vs. 9.7 percent, respectively). For secondary outcomes, the research team predefined favorable neurologic outcome as anyone who had a modified Rankin score equal to or less than 3. Although the mean modified Rankin score significantly favored the I-CPR group (5.63 vs. 5.60, p = .04), there was no difference in favorable neurologic outcome between the CCC-CPR group and the I-CPR group (7.0 vs. 7.7, respectively; p = .09).
Even though the goal of the study was to measure survival-to-hospital discharge, the research team also measured a variable called hospital-free survival, which was defined as the number of days the patient did not require readmission to the hospital during the first 30 days after discharge from the hospital. Patients who received I-CPR had significantly longer mean hospital-free survival when compared to the CCC-CPR group (1.5 days vs. 1.3 days, respectively; p = .004).
What this means for EMS providers
Two non-randomized OOH investigations in Arizona demonstrated improved survival-to-hospital discharge associated with minimally-interrupted cardiac resuscitation [5,6]. Patients in the historical control group received standard AHA recommended CPR while patients in the control group received continuous chest compressions with minimal interruptions. Although the study was interesting, many confounders could have explained the results other than the difference in CPR strategies. For example, the trial was conducted during a period when the AHA updated resuscitation guidelines. The historical control group therefore included patients who received stacked defibrillation shocks as advocated by the 2000 AHA guidelines  and patients who received single shock defibrillation attempts as advocated by the 2005 AHA guidelines . Because the experimental group received only single shocks, the significant interruptions in chest compressions within the control group receiving stacked shocks may have accounted for the reduced survival rates in that group. Additionally, the experimental group received a number of other interventions not available to the control group, such as passive oxygen administration delayed endotracheal intubation, and early epinephrine administration.
Researchers in a Kansas study found similar results . Patients receiving longer intervals of continuous chest compressions (50:2) were twice as likely to survive to hospital discharge when compared to patients who received AHA recommended CPR (30:2). As with the previous study, this investigation suffered from a number of confounders that could have explained the differences between the two groups, including the experimental group use of passive oxygen insufflation, delayed endotracheal intubation, and early epinephrine administration.
One important determinate of ROSC and neurologically intact survival is the actual number of chest compressions health care providers deliver to the patient during each minute of the resuscitation period [10,11]. In general, resuscitation strategies which provide more rather than fewer chest compressions per minute result in better outcomes. In order to accomplish this, rescuers must limit interruptions in chest compressions.
One metric that highlights the importance of minimizing interruptions is the chest compression fraction (CCF). The CCF represents the proportion of time during the resuscitation attempt that someone is actually pushing on the patient’s chest .
Observational studies have demonstrated an increased likelihood of survival with higher CCF [11,12]. However, patients in both of these studies were categorized into subgroups based on a range of CCF. The subgroup with the lowest CCF served as the reference group and all other groups were compared to this lowest group. There was no comparison of the 81-100 percent group to the 61-80 percent group. Therefore, based on these studies, one can only conclude that high-quality CPR is better than low-quality CPR.
All of the EMS personnel who participated in this study were well trained and closely monitored throughout the trial. All had to meet strict performance guidelines including keeping chest compression fractions above a certain predetermined threshold. Although statistically significant, the difference in the CCF between the two groups in the present study was small, only 6 percent. This means that for every minute of the resuscitation attempt, EMS personnel in the CCC-CPR group performed about four additional seconds of chest compressions when compared to EMS personnel in the I-CPR group. Perhaps if the difference in CCF was larger, the outcome of the study would have been different.
The researchers in the present study measured some variables introduced during hospitalization following return of spontaneous circulation. These included the use of therapeutic hypothermia, coronary catheterization with 24 hours of emergency department arrival, and the insertion of an implanted cardioverter/defibrillator (ICD). Despite the fact the researchers made no attempt to control these variables, there was no significant differences in these interventions between the two groups.
Finally, the research team did not measure or attempt to control oxygenation or ventilation during the post-resuscitation period. Abnormalities with either of these variables during this period are associated with worse outcome [13-15].
In this large randomized controlled trial, a resuscitation strategy that included continuous chest compressions did not result in survival or favorable neurologic outcome advantages when compared to standard CPR. The AHA continues to recommend a compression-to-ventilation ratio of 30:2 for health care providers .
However, it is important to note that although this study could not find survival advantages associated with continuous chest compression, it also did not demonstrate any harm associated with the strategy. If a well-trained, priority-dispatched, multi-tiered response EMS system has demonstrated success with this approach, there is no need to change. The AHA considers an initial strategy of continuous chest compressions with no assisted ventilation to be a reasonable approach in these EMS systems for the management of a witnessed OOH cardiac arrest presenting in a shockable rhythm.
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