Abstract
Helicopter emergency medical services (HEMS) frequently respond to out-of-hospital cardiac arrest (OHCA) situations. Some have speculated mechanical cardiopulmonary resuscitation (mCPR) may be able to rectify the inadequacy of human performance of cardiopulmonary resuscitation (CPR) during transport. A number of studies have examined the performance of mCPR devices in the air medical setting specifically. Many aspects of the HEMS environment seem uniquely conducive to mCPR, and a growing body of research seems to suggest mCPR holds promise for the treatment of cardiac arrest by HEMS clinicians. Simulation studies show that mCPR leads to improved CPR performance compared with manual CPR in HEMS. Case reports and the experience of several HEMS programs suggest that mCPR can be effectively integrated into HEMS care. However, further research regarding the effectiveness of mCPR in the HEMS environment and in general cardiac arrest care is needed.
In many communities, helicopter emergency medical services (HEMS) crews frequently respond to victims of out-of-hospital cardiac arrest because of the ability to provide advanced-level resuscitation and postarrest care to patients who may be far away from definitive care.
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HEMS crews may also have to provide resuscitative care for patients who enter cardiac arrest while under HEMS care. Although HEMS crews may be highly effective at providing resuscitative care on the ground, doing the same in the air (or even during ground transport) has proven elusive. A number of studies have shown that rescuers become less effective at cardiopulmonary resuscitation (CPR) during both ground and air transport.5
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This is especially true in helicopters where rescuers have to contend with confined spaces, restrictions around movement during flight, and the need to be strapped into a seat during certain phases of flight.5
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Some have speculated that mechanical cardiopulmonary resuscitation (mCPR) may be able to rectify the inadequacy of human performance of CPR during transport.3
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A number of studies have examined the performance of mCPR devices in the air medical setting specifically; this review highlights a few important studies that have interrogated the role mCPR may play in the air medical setting. Applicable items in the literature were selected through informal searches of PubMed and Google Scholar. Search terms that were used included “mechanical CPR” and “helicopter,” and results were grouped into either simulation-based studies, case reports, or multiple patient studies.The Controversy of mCPR
There is evidence suggesting that mCPR improves quantifiable CPR metrics.
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Theoretically, the link between mCPR devices and better CPR performance is intuitive; when set appropriately, mCPR devices can provide a consistent compression rate and depth and because they are strapped to patients may be less affected by motion during transport. Unlike human rescuers, mCPR devices also do not tire, and the battery life of most devices far exceeds the stamina of an average human rescuer. Furthermore, mCPR devices may lead to better workload sharing during resuscitation because the human rescuers who would have had to perform compressions are freed up to perform other tasks, such as airway management, defibrillation, medication administration, or scene control. Finally, when specifically considering the transport environment, mCPR may be associated with increased safety because providers can stay restrained. Despite having theoretical benefits, there is controversy surrounding the effectiveness of mCPR in actually improving patient outcomes.14
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Now, there is a growing concern about mCPR increasing the incidence of injuries sustained during CPR.21
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, Chun MJ, Zhang Y, Toraih EA, McGrew PR. Iatrogenic injuries in manual and mechanical cardiopulmonary resuscitation [e-pub ahead of print]. Am Surg. https://doi.org/10.1177/00031348211047507
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In recent years, mCPR devices have grown in popularity, both in the in-hospital setting and in the out-of-hospital setting. One study examining a nationwide database of emergency medical service (EMS) agencies in the United States identified a 4-fold increase in the use of mCPR devices from 2010 to 2016; specifically, around 1.9% of out-of-hospital cardiac arrest patients received mCPR in 2010. This figure rose to 8.0% by 2016.
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Multiple aspects of the helicopter environment, such as the confined environment, limited number of providers, and restrictions around movement during flight, may be uniquely conducive to mCPR use.3
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On the other hand, there are also several potential drawbacks associated with the use of mCPR in the air medical environment. For instance, there are considerations around where to keep the device on aircraft with limited storage as well as to what degree they might affect aircraft weight and balance. Research examining mCPR use in the HEMS setting has involved single-patient case reports, multiple-patient studies, and simulation/scenario-based studies.Individual Case Reports
Pietsch et al
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reported a case of a skier who was trapped in an avalanche and found in cardiac arrest by other skiers who began manual CPR. HEMS arrived roughly 1 hour after the avalanche and initiated mCPR for transport by helicopter. After further interventions were performed at the hospital, return of spontaneous circulation (ROSC) was achieved, but evidence indicated irrecoverable neurologic damage. Despite the patient experiencing an unfavorable outcome, this case shows a practical example in which mCPR was able to integrate into HEMS care, especially under harsh conditions ideally suited to helicopter ambulances (eg, mountainous terrain after an avalanche). The authors specifically speculate that mCPR has the unique ability to provide continuous chest compressions during transport over harsh terrain or during helicopter transport and emphasize the need for additional research.34
Others have also arrived at similar conclusions.35
Forti et al
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described a case in which a 53-year-old man suffered an out-of-hospital cardiac arrest and was transported by helicopter with ongoing mCPR. Resuscitative efforts were performed on scene for just under an hour when the decision was made to transport the patient by helicopter for further care and evaluation. On arrival at the receiving facility, the patient was transported to a cardiac catheterization laboratory while ongoing compressions were taking place; angiography revealed arterial occlusions, and percutaneous coronary intervention was performed on the affected vessels. ROSC was achieved after percutaneous coronary intervention, and the patient subsequently made a neurologically intact recovery.36
This case emphasizes the ability of mCPR to provide chest compressions during helicopter transport as well as during cardiac catheterization.Forti et al
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reported a case of a patient who received nearly 4 hours of mCPR (3 hours 42 minutes) and 5 hours of extracorporeal life support and was able to make a full neurologic recovery. The patient was a 31-year-old mountain climber who suffered a witnessed cardiac arrest under conditions of hypothermia. Manual CPR was initially performed for 1 cycle before mCPR initiation. The authors speculated that this may be the longest reported duration mCPR has been applied on a patient when the patient made a full neurologic recovery. Describing the use of mCPR in the helicopter environment, the authors wrote “mechanical chest compression devices can provide high-quality CPR safely during prolonged transport, given the limits of provider endurance capacity, vehicle design, and restraint systems.”41
Simulation Studies
Putzer et al
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devised a scenario involving CPR being performed on a feedback manikin during a hypothetical HEMS transport to compare the effectiveness of mCPR versus manual compressions. In their study, CPR was performed in an environment simulating a scene, a simulated helicopter flight, and an environment simulating transport to the trauma department. They found, when compared with manual CPR, that mCPR was associated with better compression quality and increased chest compression fraction. However, the time until first defibrillation was longer in the mCPR group; this is most likely because of the time needed to set up and properly configure the mCPR device.31
Gässler et al
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compared 3 different mCPR machines with manual chest compressions on a simulation manikin in an out-of-hospital cardiac arrest scenario with 4 distinct phases: CPR on scene, CPR during transport to helicopter and loading on the helicopter, CPR during simulated helicopter flight, and CPR during unloading and transport to handoff point. In this scenario, the performance of the mCPR devices far surpassed manual CPR when looking at indicators of resuscitation performance. For instance, the authors reported manual CPR was “barely possible” during the scenario; by contrast, the authors also reported “mechanical chest compression devices might be good alternatives.”37
Rethatched et al
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compared manual CPR with mCPR over the course of simulated helicopter flights. The investigators measured CPR performance and rescuer heart rate. Additionally, rescuer cognitive performance was assessed through a questionnaire and a memory test. Results showed mCPR was associated with improved CPR performance, decreased physical workload for rescuers, and enhanced cognitive performance. Despite their positive results, they emphasize the importance of training aimed at effectively integrating the device into resuscitation protocols.39
Multiple-Patient Studies
Tazarourte et al
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reported a case series of 27 patients who were transported by helicopter and received mCPR during flight. They reported that mCPR using a load-distributing band device was feasible during flight. The following items were specifically highlighted: the mCPR device caused no interference with the helicopter's avionics or navigation systems, vibrations did not affect mCPR performance, and continuous CPR was possible during all phases of flight.30
Omori et al
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compared cardiac arrest patients transported by HEMS in Japan before and after mCPR was introduced. Patients between April 2004 and June 2008 received manual CPR (n = 43), and patients between July 2008 and March 2011 received mCPR (n = 49). The use of mCPR was associated with statistically significant improvements in ROSC and survival to hospital discharge.32
Writing about this article, Putzer et al33
pointed out that resuscitation practices may have improved during the time period and a much greater number of arrests in the mCPR group were witnessed, meaning that victims who received mCPR may already have had a better chance of a favorable outcome.Winther and Bleeg
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discussed the adoption of mCPR on Danish search and rescue helicopters. They reviewed all search and rescue missions from March 2012 through February 2014 and found mCPR was used on 25 patients during the time period surveyed. The authors reported that mCPR allows providers to “maintain focus on other medical tasks such as airway management, gaining intravenous access, and administering medication,” in addition to allowing “providers to stay secure in their seats and tend to other components of the transport.”38
Rauch et al
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reported the results of mCPR use in an Italian HEMS program between June 2013 and April 2016. During this time, there were 271 out-of-hospital cardiac arrest patients treated by HEMS, and only 18 received mCPR; dislocation of the mCPR device was reported in 3 of these 18 patients. The authors emphasized the importance of patient selection for prospective recipients of prolonged mCPR-driven resuscitation.40
Pietsch et al
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described the use of mCPR in a Swiss HEMS program between January 2014 and June 2016. During this time period, 590 patients received mCPR care; many were patients who arrested or rearrested during flight. Because of this, the investigators discussed applying but not activating mCPR devices on patients who may face significant risk of experiencing a cardiac arrest during flight (prepositioning); this approach circumvents many of the challenges of applying mCPR during flight. When considering arrest etiology, the authors noted that patients who suffered nontraumatic arrests may see significantly better outcomes than patients who suffered traumatic arrests. In addition to discussing the benefits of mCPR in the helicopter environment, the authors speculated that mCPR may have a beneficial role in decreasing rescuer exposure to infectious diseases, such as coronavirus disease 2019.42
Future Directions
The research that has been conducted up until now has been helpful in identifying a role for mCPR in HEMS care. The simulation research indicates that mCPR may deliver promising improvements in CPR quality and rescuer performance, and the case reports and multiple-patient studies describe how HEMS programs have integrated mCPR within how they deliver care. However, the need for future research remains. To our knowledge, there has not been a true comparative effectiveness trial comparing mCPR versus manual CPR in HEMS; thus, the precise contributions of mCPR to resuscitative care in HEMS may be difficult to ascertain.
Several randomized clinical trials have sought to answer the mCPR versus manual CPR question in out-of-hospital cardiac arrests attended to by ground-based EMS.
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Most agree these trials satisfactorily meet expectations of equipoise—the idea that there is genuine uncertainty as to which arm of a trial is the best therapeutic option for a given patient.43
There may not be sufficient equipoise for a randomized clinical trial comparing mCPR versus manual CPR in the HEMS setting because it is clear mCPR devices are superior at providing CPR during flight. Thus, an ideal design for a trial might involve retrospectively comparing HEMS patients who received mCPR with patients who did not. The key for such a study will be how other factors are controlled for because an abundance of confounding influences on patient outcomes will limit the generalizability of the findings. The study conducted by Omori et al32
is 1 of the only instances in which mCPR was directly compared with manual CPR; however, temporal and patient-level factors that could affect the generalizability of their results have been pointed out.33
Additionally, more research examining the general effectiveness of mCPR is certainly needed. The lack of a conclusive body of evidence showing that mCPR improves outcomes may not indict the theoretical benefits of mCPR as much as speak to the limitations of current mCPR devices. It is also worth recognizing that the integration of mCPR in some air medical programs may be difficult because of the size and weight of mCPR devices and the need to conform to stringent weight/balance and storage constraints. Updated and refined mCPR devices may allow clinicians (HEMS, ground EMS, or in-hospital) to better realize the hypothesized benefits of mCPR. Specifically, future generations of mCPR devices that are smaller, lighter, or better able to be carried on board a helicopter may allow mCPR to be adopted by more programs. The idea of prepositioning mCPR devices on patients at risk of facing cardiac arrest during helicopter transport also deserves further inquiry. Prepositioning an mCPR device on a high-risk patient before takeoff may circumvent many of the difficulties of applying an mCPR device during flight.
Conclusions
Many aspects of the HEMS environment seem uniquely conducive to mCPR, and a growing body of research seems to suggest mCPR holds promise for the treatment of cardiac arrest by HEMS clinicians. Simulation studies show that mCPR leads to improved CPR performance compared with manual CPR in HEMS. Case reports and the experiences of several HEMS programs suggest that mCPR can be effectively integrated into HEMS care. However, further research regarding the effectiveness of mCPR in the HEMS environment and in general cardiac arrest care is needed.
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Article info
Publication history
Published online: August 16, 2022
Identification
Copyright
© 2022 Air Medical Journal Associates. Published by Elsevier Inc. All rights reserved.
