Abstract & Commentary
Synopsis: Trained paramedics following current CPR guidelines delivered chest compressions in a suboptimal fashion, which resulted in prolonged no flow ratios which may have contributed to the poor survival data presented.
Source: Wik L, et al. JAMA. 2005:293:299-304.
Wik and colleagues report an analysis of cardiopulmonary resuscitation (CPR) by trained professional first responders to out-of-hospital cardiac arrest. The study was conducted in Stockholm, Sweden, London, England, and Akershus, Norway. In each city, the first responder teams were staffed by paramedics; in Akershus, the team included a nurse anesthetist. A special research defibrillator was used for the study and placed in 6 ambulances in each of the 3 study cities. Each research defibrillator had an extra chest pad that was mounted on the lower part of the sternum. The chest pad was fitted with an accelerometer and a pressure sensor so that the depth and frequency of chest compressions could be recorded. Ventilation was measured by changes in transthoracic impedance after adjustment for compressions.
Immediately prior to the study, all involved personnel underwent a refresher course in advanced cardiac life support (ACLS), according to international cardiopulmonary resuscitation (CPR) guidelines. In Akersus, the cardiac arrest patients received 3 minutes of CPR before the first direct current countershock, while in the other centers, shocks were delivered without prior CPR from the team. Data from each resuscitation episode were collected and analyzed. Technical data from the defibrillator were correlated with a copy of the ambulance record and other written documentation using the Utstein format for collection of out-of-hospital cardiac arrest data.
Incomplete compression release was defined as continuous pressure above 4 kg throughout the decompression cycle. Duty cycle was defined as the percentage of time with downward movement of the chest pads divided by the total cycle time. No flow time was defined as total time minus the time with chest compression or spontaneous circulation and a ratio between the no flow time and the total time without spontaneous circulation was defined as the no flow ratio. As per guidelines, compressions were not given during rhythm analysis, defibrillator charging, shock delivery, and pulse checks.
The primary outcome measure was adherence to international guidelines for CPR. The target value for compression rate was 100-120 bpm. For depth of compression, it was 38-52 mm, and for ventilation rate it was 2 ventilations for every 15 compressions before intubation and 10-12 per minute after intubation.
Data from a total of 176 resuscitation episodes are included in this paper. The study cohort was 76% male, with a mean age of 68. Seventy-three percent of the arrests had been witnessed and 37% received bystander CPR before arrival of the paramedic team. The response time was 7 minutes, and the median number of shocks per episode was 1.5. In these episodes, the fractions of time without CPR, the no flow ratio, were 49% during the first 5 minutes and 48% during subsequent time periods. When Wik and colleagues subtracted time necessary for rhythm analysis and defibrillation, the projected no flow ratios were still high at 42% and 38%. The mean delivered compression rates were 60 per minute during the first 5 minutes and 64 per minute subsequently. However, during actual compression periods, the rates were close to target at 120 per minute (first 5 minutes) and 121 per minute (later). The mean compression depth was 35 mm, and only 27% of compressions were within the target range. Mean ventilation rates were 8 per minute and 11 per minute for the first 5 minutes and for the entire episodes, respectively.
A total of 61 (35%) patients achieved return of spontaneous circulation, 34 (19%) were admitted to the hospital and 6 (3%) were discharged from the hospital. Five of the six patients who survived to hospital discharge had nearly normal neurologic function. No patients who presented with either asystole or pulseless electric activity were discharged from the hospital alive, even though 13% of those with asystole and 19% of those with pulseless electric activity were admitted to the hospital alive. Among the 98 patients with ventricular fibrillation as their presenting rhythm, 41% achieved return of spontaneous circulation, 25% were admitted to the hospital alive, and 8% were discharged alive. There were no significant correlations between CPR quality and survival.
Wik et al conclude that trained paramedics following current CPR guidelines delivered chest compressions in a suboptimal fashion. This resulted in prolonged no flow ratios which may have contributed to the poor survival data presented.
Comments by John P. DiMarco, MD, PhD
Over the last 30 years, there have been efforts made to improve cardiac pulmonary resuscitation for patients with out-of hospital and in-hospital cardiac arrests. This paper and an accompanying paper by Abella and colleagues (JAMA. 2005;293:305-310), which dealt with inhospital cardiac arrest demonstrate that performance of CPR, even by trained individuals, does not match guidelines and is associated with poor overall results.
Several comments should be made about these papers. In patients who arrest out-of-hospital, the response time and the initial rhythm are the critical factors. Over time, there has been a trend toward a higher proportion of patients with cardiac arrest having either asystole or pulseless electric activity at the time of presentation. These patients have a very poor prognosis as seen here, even if spontaneous circulation can be briefly established. In patients with ventricular fibrillation, the key factor is response time and time to defibrillation. In this study, the mean response time was 7 minutes and, therefore, one would expect a relatively low survival to hospital discharge. In the in-hospital setting, patients who arrest are often critically ill with other diseases and their prognoses are largely determined by the underlying disease. Because of this, long-term survival rates after in-hospital cardiac arrest are also low.
How to improve survival after cardiac arrest remains a major question. There have now been a number of studies which have shown that making the protocol for CPR more complex results in only minimal improvements in survival. Even for highly trained paramedics and hospital workers, as in these papers, compliance with complex guidelines is difficult in the arrest situation. Therefore, it seems appropriate that the new emphasis in resuscitation should be early defibrillation, with automatic external defibrillators (AEDs) operated by lay responders with less emphasis on CPR techniques. This may shorten the response time and bring defibrillation to arrest patients with ventricular fibrillation, the group most likely to respond favorably. AEDs may now be purchased without a prescription and, if prices become more reasonable, should become widely distributed in the community.
Dr. DiMarco, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville, is on the Editorial Board of Clinical Cardiology Alert.