Mechanical versus manual chest compressions for cardiac arrest: a systematic review and meta-analysis

The goal of CPR treatment for CA patients is to achieve ROSC and normal neurological function as early as possible while minimizing end-organ damage and dysfunction in the interim. Several animal and human studies have demonstrated an inverse relationship between poor chest compression quality and short-term survival [35‐37]. The high quality of CPR has been emphasized in the American Heart Association (AHA) guidelines and emergency cardiovascular care [38]. However, Hightower et al. observed significant fatigue after only one minute of chest compressions on a mannequin. Correct chest compressions were performed 92 % of the time during the first minute, 67.1 % during the second minute and 39.2 % during the third minute [39]. Rescuer fatigue has been identified as an important factor to poor CPR quality. The use of mechanical chest compression devices has been proposed to provide high-quality chest compressions without the interruptions and fatigue, meanwhile the resuscitation efforts can be facilitated by freeing the hands of the rescuer from manual chest compression. For the same reasons, safety increases during transport in a moving ambulance for OHCA patients. Some data from animal and human observational studies suggested that mechanical chest compressions might be superior to manual chest compressions in cardiac arrest [14‐19]. The international guidelines published in 2010 suggested the devices could be considered as part of an overall strategy to improve CPR quality [38]. In contrast, several larger RCT studies concluded that mechanical CPR did not result in improved outcomes compared with manual CPR in recent years [32‐34]. This systematic review and meta-analysis sought to assess whether there was a difference between mechanical and manual chest compression with respect to CPC, ROSC, survival to hospital admission and discharge.

Twelve studies (8 randomized control trials, 2 phased prospective cohort trials, one phased prospective cohort trial and one descriptive controlled trial) were identified after the search of the literatures, comprising five studies about LUCAS, four about AutoPulse, three about Thumper and one about vest CPR (one paper including both LUCAS and AutoPulse). The publication dates of these included studies span over 40 years. The results of this meta-analysis indicated no difference is found in CPC scores, survival to hospital admission and survival to discharge between manual and mechanical CPR for OHCA patients. The data on achieving ROSC in both of in-hospital and out-of-hospital setting and survival to discharge for in-hospital patients suggested poor application of the mechanical device. Considering the heterogeneity in types of mechanical devices used, we identified studies that reported LUCAS and AutoPulse in ROSC with mechanical chest compressions compared with manual chest compressions respectively, the results shown that OHCA patients receiving manual resuscitation were more likely to attain ROSC compared with AutoPulse; however, the difference was not significant between LUCAS and manual resuscitation. On the whole, available data from clinical trials did not provide sufficient evidence to permit conclusions on the effectiveness of mechanical chest compressions as compared with manual chest compressions, which was similar to the conclusion of another recent review and meta-analysis about OHCA patients [40]; in contrast, for in-hospital CA patients, the use of mechanical chest compression could not be recommended. The limited amount and varied definitions of long-term survival and neurologic function data for each respective study prohibited the use of the data as the outcome variable in this meta-analysis.

Many factors affect the chances of survival after cardiac arrest, including early recognition of arrest, effective cardiopulmonary resuscitation and defibrillation, and post-resuscitation care. A critical issue is the delay between collapse and the start of the intervention. For OHCA patients, witnessed CA receiving bystander basic life support might improve outcome [41]. One of these hypotheses is that interruptions in CPR during device deployment could cause reduced cardiac and cerebral perfusion [1]. It is important to reduce the interval between collapse and the start of chest compression. However, there will always be a delay from the arrival of the rescuer to setting up the equipment and giving the first treatment according to field conditions, which might increase cardiac instability and impair cerebral microcirculation. Secondly, several studies reported that they failed to find any significant difference between manual and mechanical in their outcome of survival or survival to discharge. A possible explanation for these unexpected results advanced by the authors is a Hawthorne effect for manual CPR, which means a type of reactivity in medical rescuers modify or improve an aspect of their behavior in response to their awareness of being observed [42, 43]. Almost all of the included studies did not have the quality of CPR monitoring in place at the time, these data were not collected or reported specifics on how manual CPR was performed in the control group. Although considering the Hawthorne effect, the meta-analysis was unable to show any superiority of mechanical device, which mean the mechanical chest compression might not be better than high-quality manual CPR. Mechanical chest compression should not be seen as a replacement for high quality manual CPR, but rather a supplemental treatment in an overall strategy for treating CA patients. Thirdly, it is also increasingly recognized that although defibrillation is the definitive treatment for ventricular fibrillation, its success is also dependent on adequate circulation [44]. Thus, effective CPR is often a prerequisite for effective defibrillation. Patients presenting in ventricular fibrillation have relatively high survivability with early defibrillation [45]. In practice, the device is usually applied in patients who do not respond to initial defibrillation and require prolonged CPR. Patients in prolonged cardiac arrest who are successfully resuscitated would be expected to have poorer neurological status on discharge compared to those who respond immediately. Finally, management of patients following resuscitation from CA is complex and requires specialized institutions capable of providing advanced care therapies. Patients with ROSC are treated with mild hypothermia to 32 ~ 34 °C for 24 h, if no contraindications are present. Acute coronary angiography is considered during the first 48 h and, if indicated, a percutaneous coronary intervention is performed. Managing these patients achieving ROSC is challenging and requires a structured approach. Clinical recommendations for CPR, including the nature of manual chest compression, have changed drastically over the past 10 to 15 years [38]. The dates of these included studies span over four decades, strategy of post-resuscitation care for ROSC patients has improved. Those might influence the survival of discharge and neurological function over years.

In this meta-analysis, there were some limitations. The first limitation was that some of the included studies were prospective observational trials or phased controlled trials. It was possible that selection bias could be introduced that the paramedics tended to have a lower threshold for initiation of resuscitation. A second limitation was that none of studies were blinded. Because the rescuers who decided when to initiate CPR were not blinded, introducing the possibility of rescuers preferential application of a device to patients thought to have a very poor prognosis in the hope that use of the device might lead to better outcomes than attained with standard care. Thirdly, these included studies were conducted across nearly 50 years, which demonstrated marked heterogeneity in types of mechanical devices used, timing of device application, CPR quality of manual chest compression and post-resuscitation management. Although we had made a subgroup analysis according to the types of mechanical devices (LUCAS, AutoPulse and Thumper) for OHCA patients, the heterogeneity could not be eliminated and would reduce the statistical power of the approach based on the limited data. Finally, very limited data were available from those studies comparing long-term survival and neurological function score, results from these studies were not pooled.