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[每周一问]NO.12-Cardiopulmonary resuscitation (CPR)

Cardiopulmonary resuscitation (CPR) is a skill that has significant impact on asystolic patient survival. This week, we'll discuss some recent changes in the performance of this skill. Today we'll discuss some basic facts regarding CPR.
1.What is the primary determinant of CPR effectiveness?
2.How much time may elapse following cardiac arrest for patient survival to occur?
3.Is CPR with only chest compressions effective?
心肺复苏（CPR）
CPR对心搏停止病人的存活影响显著。本周，我们将讨论在这方面的一些新变化，今天我们讨论关于CPR的基本情况。
1.评价CPR效果的基本决定因素是什么？
2.对病人存活影响的心跳停止时间为多长？
3.仅仅实施胸部按压CPR是否有效？

Cardiopulmonary Resuscitation — Strengthening the Links in the Chain of Survival

[每周一问]NO.12-Cardiopulmonary resuscitation (CPR)

1.评价CPR效果的基本决定因素是什么？
最近研究的室颤病人，心肌和脑灌注是CPR效果的基本决定因素[1]。而脑和纤颤心脏继续消耗ATP和其他能源，这是确定的。如果心肌缺血时间过长，心肌细胞死亡，此时的电除颤只会产生无脉性电活动或心搏停止。
同样，发生于医院之外的由于室颤导致的心跳停止的总的生存率的重要影响因素包括是否有目击者发现并开始CPR，以及心脏除颤多久完成。

2.对病人存活影响的心跳停止时间为多长？
Eisenberg等[2]的一经典研究发现，院外发现病人因室颤发生心跳停止时，如果CPR能在4分钟内进行并8分钟内开始实施确定性治疗，43%可以存活出院。相比之下，如果CPR在8和16分钟开始，只有7%和0%的病人存活。

3. 仅仅实施胸部按压CPR是否有效？
过去十年，人们试图通过实验室研究评估单纯胸外按压行CPR的价值。在室颤导致的心跳停止的猪的模型中，发现24小时存活率在单纯胸外按压组与合并呼吸辅助组相近[3]。最近，Hallstrom等[4]通过一城市急救医学服务机构开展的研究，随机化通过电话指导目击者实施带或不带有呼吸辅助的CPR，存活出院作为研究的基本终结点，单独胸外按压CPR者241名，呼吸辅助CPR者279名病人，存活率分别为14.6%和10.4%（P = 0.18，无显著意义）。同样，landmark研究也支持单独胸外按压CPR可以应用于目击者实施CPR的情况，并与告知的CPR的方法有关。这个研究证明对于目击者实际实施CPR的意愿有重要影响。在对975名告知其假定知道如何实施CPR调查发现，如果仅仅要求对陌生人进行胸外按压，68%调查者确定会实施CPR；而如果需要口对口辅助呼吸时，只有15%愿意这样做[5]。

What is the primary determinant of CPR effectiveness?
In patients with ventricular fibrillation of recent onset, myocardial and cerebral perfusion are the primary determinants of CPR effectiveness (1). This is true as the brain and the fibrillating heart continue to consume ATP and other energy sources. Should myocardial ischemia continue too long, myocyte death occurs, and electrical shock after this will only result in pulseless electrical activity or asystole.
As such, the major determinant of overall survival after witnessed out of hospital cardiac arrests due to ventricular fibrillation include whether a bystander initiates CPR, and how quickly defibrillation is accomplished.
How much time may elapse following cardiac arrest for patient survival to occur?
In a classic study by Eisenberg et al. (2) observing patients with out-of-hospital cardiac arrest due to ventricular fibrillation, 43% survived to hospital discharge if CPR was initiated and definitive therapy was delivered in four and eight minutes, respectively. By contrast, if CPR was initiated in 8 or 16 minutes, 7% and 0% of patients survived.
Is CPR with only chest compressions effective?
In the past decade, laboratory studies have attempted to evaluate the value of CPR with chest compressions only. In the swine model of cardiac arrest induced by ventricular fibrillation, survival at 24 hr. was noted to be similar to when CPR included only chest compression as when it involved assisted breathing and chest compressions (3). Recently, and of immense importance, Hallstrom et al. (4) in a trial conducted through an urban emergency medical services system, randomized telephone dispatchers to inform bystanders to perform CPR using chest compressions with or without assisted breathing. Using as their primary endpoint survival to hospital discharge, of the 241 and 279 patients in the CPR alone and with assisted breathing, respectively, the rate of survival was 14.6 versus 10.4% (P = 0.18 i.e. a non-significant difference). As such, this landmark study supports the idea that CPR with chest compressions alone may be applicable to the setting of the bystander-initiated CPR, and may have implications to the way CPR is taught. This demonstration may also have an important impact on bystanders willingness to actually perform CPR. In a survey of 975 laypersons instructed to assume that they knew how to perform CPR, 68% reported that they would definitely perform CPR on a stranger if only chest compressions were required, whereas only 15% would do so if mouth-to-mouth assisted ventilation was also necessary (5).
References:
1.  Ewy GA. Cardiopulmonary resuscitation-strengthening the links in the chain of survival. N Engl J Med 2000;342:1599-601.
2.  Eisenberg MS, Bergner L, Hallstrom A. Cardiac resuscitation in the community. Importance of rapid provision and implications for program planning. JAMA. 1979;241(18):1905-7.
3.  Berg RA, Kern KB, Hilwig RW, Ewy GA. Assisted ventilation during 'bystander' CPR in a swine acute myocardial infarction model does not improve outcome. Circulation. 1997;96(12):4364-71.
4.  Hallstrom A, Cobb L, Johnson E, Copass M. Cardiopulmonary resuscitation by chest compression alone or with mouth-to-mouth ventilation. N Engl J Med. 2000;342(21):1546-53.
5.  Locke CJ, Berg RA, Sanders AB, et al. Bystander cardiopulmonary resuscitation. Concerns about mouth-to-mouth contact. Arch Intern Med. 1995;155(9):938-43.
Site Editor: Stephen B. Corn, M.D. and B. Scott Segal, M.D.
Department of Anesthesia, Harvard Medical School
Founders and Editors-in-Chief: Stephen B. Corn, M.D. and B. Scott Segal, M.D.
Department of Anesthesiology, Perioperative and Pain Medicine, Harvard Medical School