Progress in resuscitation: an evolution, not a revolution.

THERE WAS A TIME NOT LONG AGO WHEN THE QUALity and quantity of chest compressions did not seem that important during resuscitation—at least not in comparison with early defibrillation. A ventricular tachyarrhythmia is the initiating event in more than 80% of patients who develop out-of-hospital, primary cardiac arrest during ambulatory electrocardiographic monitoring. Survival declines rapidly if defibrillation is not performed in the first few minutes (defibrillation phase) because myocardial adenosine triphosphate (ATP) levels begin to decrease as fibrillating myocardial cells continue to consume ATP at a nearly normal rate. As a result, ventricular fibrillation (VF) is the presenting rhythm in only 22% to 35% of out-of-hospital cardiac arrest cases when emergency medical services (EMS) personnel arrive on scene. By this time, myocardial ATP stores have often declined to critical levels and a defibrillation shock will usually terminate VF but frequently results in either asystole or pulseless electrical activity as cells run out of high-energy phosphate “fuel. ” During this circulatory phase, a brief period of effective chest compression before defibrillation can boost myocardial ATP stores and increase the likelihood that a perfusing rhythm will follow defibrillation. Thus, the strategy for resuscitation from cardiac arrest has evolved from “shock first and often” to a time-critical, orchestrated approach of high-quality cardiopulmonary resuscitation (CPR), defibrillation, and postresuscitation care. This new approach highlights the importance of highquality, minimally interrupted chest compressions to maximize tissue oxygen delivery and intracellular high-energy phosphate levels. Conventional, closed-chest CPR is at best imperfect, producing hemodynamic change similar to that observed in cardiogenic shock. Minimal interruption of chest compression helps to maximize tissue oxygen delivery and, hence, myocardial high-energy phosphate levels. Aufderheide et al showed that both high-quality chest compression (adequate depth, force, and duration) and complete chest wall decompression are needed to maximize stroke volume and improve venous filling during the upstroke, respectively. The odds of survival from cardiac arrest increase when continuous, or nearly continuous, high-quality chest compressions are performed during resuscitation. Abella et al used a monitor/defibrillator with additional sensing capabilities to measure CPR quality (chest compression rate and depth, ventilation rate, and the fraction of cardiac arrest time without chest compressions) during resuscitation in 67 patients who experienced in-hospital cardiac arrest. The authors found that the quality of chest compression was inconsistent and often did not meet published guideline recommendations, even when performed by well-trained hospital staff. In a follow-up study, the same authors used a handheld recording device to measure chest compression rate as a surrogate for CPR quality in 3 different hospitals and found that higher chest compression rates correlated significantly with initial return of spontaneous circulation in 97 in-hospital patients with cardiac arrest. Thus, chest compression quantity and quality are critical determinants of survival from cardiac arrest. Positive pressure ventilation may not be necessary during the first few minutes of CPR because spontaneous agonal respirations often contribute to respiratory exchange of gases. Chest compression alone with a patent airway generates significant minute ventilation and the quantity of oxygen needed is reduced significantly during low blood flow states. Chandra et al assessed the time course of change in arterial blood gases during resuscitation in a canine experimental VF model and found that chest compression alone during CPR can maintain adequate gas exchange to sustain the oxygen saturation level above 90% for at least 4 minutes. Survival from out-of-hospital cardiac arrest is as good in humans when bystanders perform only chest compressions compared with when bystanders perform both chest compressions and mouth-to-mouth ventilation. In this issue of JAMA, Bobrow and colleagues provide an analysis based on a before and after comparison as well as a protocol compliance analysis of out-of-hospital